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View Full Version : GH2 Worth buying a Tamron 17-50 2.8?



Admir
03-12-2012, 04:19 AM
Hi!

I had a chance to play with the Nikon 17-55 2.8 a couple of days ago. I don't have the money right now to buy it so I am lookin for the next best thing that I can afford.. Reading a lot of reviews and the Tamron 17-50 non VC looks like a steal for the money! I'm looking for the one that's 67mm in the front since that one is non-VC.

Does this lens preform good on the GH2? I understand that it will not be as good as the Nikon but judging what people say it's not that different (besides the build quality).

Comparing this lens with old Nikon E primes such as 28mm 2.8, 50mm 1.8, and 100m f 2.8, how good is the Tamron?

Gerson
03-12-2012, 08:41 AM
I just bought this lens and haven't had a chance to shoot very much with it. My initial impression, for what it's worth, is that it's surprisingly soft wide open, but excellent otherwise. That said, I've never used the Nikon 17-55, nor do I have experience with the Nikon E primes.

ade4all
03-12-2012, 09:06 AM
its a good sharp lens through most of the zoom but does not have as pleasing a bokeh as the nikon, in my opinion anyway

Admir
03-12-2012, 11:07 AM
Thanks for your input guys!

As far as the soft image goes, I think that the VC version suffers much more from it than the non VC according to users online... I'm out after a fast allround lens that gives nice and pleasing footage, and for this price I can't see how it can be beaten.

mr bill
03-12-2012, 12:45 PM
It's a great lens - I bought one for my canon and compared against the highly efs regarded canon equivalent, it had more contrast, better colour - just more all-round bite. I think you'll like it.

Aki_Hartikainen
03-12-2012, 12:47 PM
I've had sharp images aperture wide open (f2.8) from Tokina AT-X series zoom lenses. If full aperture sharpness is important, maybe have a look what Tokina could offer.

Admir
03-12-2012, 02:23 PM
I've been looking at the Tokina but that's a bit to much money... Right now I can get a second hand Tamron for 220 dollars...

But the Tokina lenses looks really promising, definitly something to get in the future!

M. Gilden
03-12-2012, 03:33 PM
I think I've found the Tamron relatively sharp at 17mm actually, even wide open compared to some vintage primes. Its at the far end, 50mm, that it appears soft wide open.
At least in my eyes. For the money, this one is pretty indispensable to me. Even if just to use as a sharp 17mm F/2.8!

Gerson
03-12-2012, 04:15 PM
Yes, when it looked soft wide open I was at the long end (not quite 50mm, but awfully close). Please don't let my one criticism sway you too much. It's a great lens!

Admir
03-13-2012, 05:52 AM
hehe no worry Gerson, I still like this lens! This might come as a stupid question, but would you say that this lens gives "cinematic" quality to the image or is it more of a digitalcamera/budget look to it?

Tass
03-16-2012, 09:26 AM
Does this lens keep the focus while you zoom in and out? Some lenses you have to refocus every time you zoom..

Stroh
03-16-2012, 10:01 AM
the lens is parfocal, and performs quite well wide open closer to the wider side. my main gripe with this lens is the extremely short focus pull, leaves much to be desired especially for video purposes, unless you're shooting a deep DOF. i would check out the tokina 16-50mm f2.8, that lens has peaked my interest recently,

Tass
03-16-2012, 10:21 AM
Lol I have an oppurtunity to buy the tamron for 70 bucks since the focus motor is dead, and I would never usenthe AF anyway so I guess that's a steal for the money... So parfocal means that the focus will stay the same while zooming?

M. Gilden
03-16-2012, 10:34 AM
Lol I have an oppurtunity to buy the tamron for 70 bucks since the focus motor is dead, and I would never usenthe AF anyway so I guess that's a steal for the money... So parfocal means that the focus will stay the same while zooming?

$70 is a STEAL for this lens. Yes, parfocal means it will stay focused as you move along the zoom range. However, I believe Stroh is incorrect in stating that this one is parfocal.
Most zoom lenses are not, as they are very complicated to manufacture and have very little use outside of the video world. From personal experience, I have to readjust focus everytime the zoom is moved.

Aside from some folks using old TV lenses with adapters, I haven't really seen many parfocal lenses around.

Stroh
03-16-2012, 11:02 AM
hmm if the focus changes while zooming it is very minimal, i did not experience a noticeable shift in focus at higher F-stops throughout the zoom range, though admittedly i only had the lens for a few months before i sold my canon setup.

DrDave
03-16-2012, 11:23 AM
The best deal on super fast, super zoom, video friendly, parfocal, focus tracking, silent lenses is a camcorder. I have a large number of zooms, but I never use them on the GH2, I just put primes on. I realize the need for zoom, so I put six primes in a carrying case and fitted them with adapters. You just don't get the same DOF at F2.8 and most of those lenses need to be stopped down to F4. I definitely can recommend the Kobori 28-200 (Vivitar Label, $35 used), but I still use my primes, I mean, they are better lenses. I supplement the primes+GH2 with the Canon G10 for times when I need a smooth, silent zoom. Plus there is no video noise or aliasing. Lpowell has had good results with his Leicasonic, however.
The bokeh is really important on zoom lenses. If you use it wide open, your backgrounds may look messy in certain situations, so check that out.

Tass
03-16-2012, 12:17 PM
I have an HMC150 when I need a "pro" zoom camera for ENG work and so on. I just find my self to many times shooting with the GH2 and not having time to change the lens, and when I try to change them fast (and it never goes fast when you're alone) you miss those sweet moments...

I should have my 70$ tamron next week... In any case it's worth taking the risk for 70$ =P. I've seen that some people claim that the tamron actually is not 2.8 when open, but more like f3.5, this sounds strange but still plausible since it is really cheap for the money?

This video made me really want this lens: http://vimeo.com/21379553#comment_6808915

nyvideo
03-16-2012, 12:37 PM
Maybe this has been covered, but when I go to the B&HVideo site they list half-a-dozen Tamron 17-50mm/f2.8 lenses, none designated as for the Panasonic GH2. If you purchased this lens new, which would be best to select? What about adapters?

Thanks.

Tass
03-16-2012, 01:03 PM
Well I am buying a tamron with nikon mount. My gh2 has a adapter for nikon mounts with apperture ring so I can control the F stop on the lens. Don't go with the VC version since a lot of folks say that it is softer, and you won't have any use of the VC function anyway... The one that's heading my way is called Tamron AF SP 17-50/2,8 XR Di-II LD Aspherical (IF)

Stroh
03-16-2012, 02:26 PM
nikon mount would be your best bet, and tamron notified me that the lens is indeed parfocal.

Aki_Hartikainen
03-16-2012, 09:47 PM
The lens could be parfocal but the adapter not necessarily. I use Minolta MD 35-70 f3.5 Constant Aperture for most of my filming and the zoom should be parfocal but isn't because of the wider tolerances in the low cost Pixco adapter.

Admir
03-17-2012, 01:39 AM
Talking about adapters; is it true that when you attach an adapter for a different lens mount you lose a full stop or more light since the adapter eats light depending on how much it extends?

GrahamH
03-17-2012, 02:29 AM
Talking about adapters; is it true that when you attach an adapter for a different lens mount you lose a full stop or more light since the adapter eats light depending on how much it extends?

In the context of GH2 mount adapters, no it's not true. Those adapters are just empty metal rings with no lenses, designed to hold the lens the same distance from the film plane as they would be on a full size DSLR. In terms of light gathering and exposure, an F2.8 lens stays F2.8.

What you are likely referring to are teleconverters, containing optical elements, that increase focal length and therefore reduce f-stop.

Aki_Hartikainen
03-17-2012, 03:08 AM
But if you mount a lens made for a larger sensor size in front of a sensor with surface area of only 1/4 (2x crop), 3/4 of the light of the lens will go past the sensor and does not help illuminate the image. The f2.8 is for a light circle with certain diameter. If the sensor does not cover full light circle of the lens, one actually loses f-stops within the camera system, in this case 2 f-stops for 2x crop sensor.

Sensitivity of the sensor then starts to have a role, and because cameras with different sized sensors have been matched reasonably well, this reduction of light gathering power is no longer seen easily. 2x crop sensor can have the same amount of light gathering pixels as a full size sensor. To avoid complicating things too much it can be said that a f2.8 lens for full size camera remains the same for crop size camera.

But in purely optical devices 2x crop or magnification would indeed mean reduction of 2 f-stops (2x optical extender, for example). The optical extender does the exact same thing as a smaller sensor, crops and magnifies image. For smaller film size this reduction in light gathering power by smaller surface area would be seen when using the same projector and candle power to project same size images. For smaller film size the projector would have to have greater distance from the screen, hence two stops dimmer projected image on the screen (all else being equal).

DrDave
03-17-2012, 12:11 PM
My Rokkor 50/1.4 is a half stop faster than my Olly 45mm (measured at 2.8) which cost ten times as much. I suspect that this is because of the size of the front element of the glass (gathering more light), but I have no idea, really. Anyway, you will not lose any speed. Some lenses are slower or faster than their rating. Maybe this Rokkor is really 1.2, have to test that some day if they ever make a m4/3 1.2 that I can afford.
You MAY have to adjust the focus. Most primes work very well, but a few zooms and the odd prime need to have the infinty focus tweaked slightly. If you don't shoot infinity, it is not a problem. Of course, it could be that the lens need to have the infinity focus reset anyway. Zooms are more susceptible to focus errors than primes.

Aki_Hartikainen
03-17-2012, 01:00 PM
My Rokkor 50/1.4 is a half stop faster than my Olly 45mm (measured at 2.8) which cost ten times as much. I suspect that this is because of the size of the front element of the glass (gathering more light), but I have no idea, really.

M4/3 lenses can focus more light on smaller circle, which in turn becomes brighter. They should be brighter and the comparison directly from the lens rating should no longer be valid, because the rating is for different sized light circles.

This is the reason a f0.95 25 mm exists for m4/3, but the fastest equivalent for full frame is f1.4 (2 f-stops difference, as sensor area indicates). One could easily test by taking a lamp in hand and keeping lens back to a wall. Direct light through the lens and take the lens farther from the wall. The light circle grows, but becomes dimmer.

Lpowell
03-17-2012, 02:51 PM
But if you mount a lens made for a larger sensor size in front of a sensor with surface area of only 1/4 (2x crop), 3/4 of the light of the lens will go past the sensor and does not help illuminate the image. The f2.8 is for a light circle with certain diameter. If the sensor does not cover full light circle of the lens, one actually loses f-stops within the camera system, in this case 2 f-stops for 2x crop sensor.
No, the 75% of light that's lost is in the outer perimeter of the image circle that is cropped out of the Four Thirds frame. Since there is no light lost within the image sensor's frame, there is no reduction in exposure. The only reduction is in the lens' Field of View, compared to a full-frame sensor.

As an analogy, consider what happens when you crop out the center quarter of an image in Photoshop, reducing it to half the width and height. Is the remaining image reduced in brightness or altered in any way?

Aki_Hartikainen
03-17-2012, 03:11 PM
No, the 75% of light that's lost is in the outer perimeter of the image circle that is cropped out of the Four Thirds frame. Since there is no light lost within the image sensor's frame, there is no reduction in exposure. The only reduction is in the lens' Field of View, compared to a full-frame sensor.

As an analogy, consider what happens when you crop out the center quarter of an image in Photoshop, reducing it to half the width and height. Is the remaining image reduced in brightness or altered in any way?

That's a good analogy and explains what happens in electronic image systems and why the apparent brightness can be maintained throughout the processing and viewing chain. However, the cropped image has been exposed with fewer photons, hence it must be dimmer. Unless there was more sensitive surface to receive fewer photons.

In Photoshop consider the post card sized window is illuminated by 10 watts. When you enlarge the image to full screen and illuminate it with only the same wattage, the exposure would be lower and full screen image dimmer. For a LCD display the full screen image is illuminated not with 10 watts but with 50 watts, for example. An optical system would only have the original 10 watts worth of photons from the subject. Using amplification and increasing wattage must be used to adjust brightness to same level as larger image that received photons worth 50 watts for exposure.

What comes in is the same that goes out all else being equal. A telephoto lens receives fewer photons from the subject than normal lens, hence telephoto lens is dimmer unless relative aperture size is increased. Same principle applies for different film and sensor sizes.

Aki_Hartikainen
03-17-2012, 04:13 PM
Camera engineers have made sure different cameras output very similar brightness. Jpeg encoding requires great precision for brightness for best results. However, few clues still remain that tell us that a 50 mm f2 normal lens does not become a 100 mm f2 by halving the sensor width. The most obvious clue is the depth of field. Had the 50 mm f2 lens turned into 100 mm f2, depth of field should have become shorter. When this does not happen, the depth of field remains the same, this tells us that the 100 mm equivalent lens is not f2, but actually the equivalent of 100 mm f4.

When we don't see reduction in apparent image brightness is because of the fine camera engineers adjusting the brightness to same level in camera using onboard electronics. What this also means is that potential for m4/3 lenses to be brighter exists, and this can be seen in the Nokton 25 mm f0.95, as well as a few other lenses. Optical image stabilization often prevents using large apertures, hence O.I.S. lenses being rather slow.

mr bill
03-17-2012, 04:45 PM
Please someone shoot some trees

DrDave
03-17-2012, 08:07 PM
If I put my camera in full manual and swap out lenses, they all read slightly different, but the camera isn't doing anything that I can see, and my 50mm is reading slightly faster, not slower. My 55mm MF reads the same as my 45mm Olly. That means the lens is the difference.

Aki_Hartikainen
03-17-2012, 08:19 PM
Lenses are different and ratings are different, but my point was that if you put in 40 photons and get 40 photons out (full frame), and then put 10 photons in (2x crop camera, 1/4 surface area) you can only expect to get 10 photons out. When you get 40 photons out, the camera amplifies the photons by factor of 4, which is the equivalent of 2 f-stops. It does not matter how the amplification is done, if you squeeze 16 mp photosites in 1/4 area, that is one form of amplification.

Optically 50 mm f2 lens for full size camera becomes the equivalent of 100 mm f4 on a 2x crop camera, but electronically difference in brightness is done away. Perhaps better think of it only if you are real interested in optics and electronics. Cameras have been matched as closely as possible and are within spesifications. Comparing lenses is always a good idea.

If there is something to consider in this is that the F-rating for the lens does not determine it's brightness. It only determines the maximum aperture / focal length ratio. Brightness is determined by the size of the light circle that the lens outputs. The smaller the light circle, the more focused is the light, thus increased intensity and brighter lens.

nothing
03-18-2012, 09:38 AM
Optically 50 mm f2 lens for full size camera becomes the equivalent of 100 mm f4 on a 2x crop camera, but electronically difference in brightness is done away

I'm sorry but you are 100% wrong about crop affecting stop. The crop and image circle size have nothing to do with the f-stop, t-stop or resulting image brightness, "equivalent" (I'm so sick of this crop equivalent-speak, this is a perfect example of the confusion it causes) or not.

Aki_Hartikainen
03-18-2012, 10:32 AM
Crop doesn't affect f-stop of the lens, but it should if what many people claim was correct. Does 50 mm f2 and 100 mm f2 have the same depth of field from the same distance? If not, then 50 mm f2 can not be the equivalent of 100 mm f2 on a crop camera. It would be the equivalent of 100 mm f4. Optically speaking.

The problem with the whole issue is the lack of basic understanding of crop and magnification factor involved. When there is crop, the image has to be magnified. Magnification is what eats brightness in optical devices, but you can adjust it electronically to the same brightness and that's what is done on the crop cameras.

40 photons of brightness in = 40 photons of brightness out (full size)
10 photons of brightness in = 10 photons of brightness out -> adjusted to 40 photons of brightness out (crop camera)

It is really this simple, if you allowed it to be.

Aki_Hartikainen
03-18-2012, 11:06 AM
Let's not forget this is a camera system and the lens is only one part of it. One can not expect everything to remain the same when you take one part of a system and install it on a different system. The area of the film or sensor is part of the system's light gathering power. If you reduce the area, light gathering power can not remain the same. Optical properties of the system have changed. Smaller area does not gather as much light as larger area.

We can adjust so that often the end result looks similar enough, and that's what matters. We can get similar results from different systems, but that does not mean the systems are the same.

Will Turner
03-18-2012, 11:57 AM
Camera lenses are measured in F stops, which is a theoretical number. This explains the difference between photographic lenses, it depends how accurate the calculations were and how well manufactured the glass is.

Cinema glass is however measured in T stops, which is the real number.

Sensor size does nothing to lenses. A 50mm F1.4 is a 50mm F1.4 on ANY size sensor. Smaller sensors crop the image, EXACTLY THE SAME as if you would crop an image in photoshop. The aperture doesn't change and neither does the focal length.

Aki_Hartikainen
03-18-2012, 12:10 PM
Lens remains the same but camera does not. Camera captures the image, not the lens. One has to consider the whole camera system, not just one part of it. Differences in brightness between lenses come partly from different sized light circles, which determine the brightness of the lens.

If you could condense the light circle into smaller area, it would be brighter. Accepted?

Aki_Hartikainen
03-18-2012, 12:40 PM
I made the image for your consideration. Same lens, same light, same f-stop. Allow the business card to represent a m4/3 sensor. You can now see that a genuine m4/3 lens made for that sensor size would produce brighter image with the exact same light and same f-stop.

http://www.fourseasonshd.com/lightCircle.jpg

Aki_Hartikainen
03-18-2012, 01:08 PM
The conclusion is that we need to start to consider the diameter of the light circle that the lens outputs to determine brightness of the lens. F-stop is not enough. Clearly there are brighter lenses for the same f-stop, as was noted above by others too. This is caused by lens outputting light circle with different diameter.

A genuine m4/3 lens could in theory be 2 f-stops brighter than the same lens for full frame, if the light circle was made to match the m4/3 sensor area. This is seen in the Nokton f0.95 25 mm lens. To make the lens work for full frame would require enlarging the light circle, which would make the lens dimmer. Now these things go hand in hand, we can not just change the last lens element for different magnification and brightness. The whole lens has to be re-designed for different sensor area. Something that not many lens makers are willing to do.

They just use the same lenses and conveniently forget about to report brightness difference for images captured by different sensor sizes. It doesn't help that people keep insisting that "the lens is the same lens". Sure, but the camera is not.

nothing
03-18-2012, 01:14 PM
The lens to sensor distance does not change, as you had it do in your example. Read up on "flange distance".

The image circle that a lens makes does not change, different cameras just utillize different size chunks of the middle of that image circle.

Aki_Hartikainen
03-18-2012, 01:35 PM
You misunderstand the basics. The lens to sensor distance does not change, as you had it do in your example. Read up on "flange distance".

The image circle that a lens makes does not change, different cameras just utillize different size chunks of the middle of that image circle.

I understand it perfectly. Different cameras utilize different chunks of the light circle and therefore capture different amount of light and photons. Hence different brightness, unless adjusted.

The only thing that changes in the image above is the diameter and area of the light circle that the lens outputs. This made the brightness different. If you took a lens for full frame camera, that would be the brightness in the lower image for m4/3 image. Whereas if you took a lens made spesifically for m4/3, that would be the brightness in the top image. Same f-stop.

nothing
03-18-2012, 01:40 PM
The only thing that changes in the image above is the diameter and area of the light circle that the lens outputs.

How did you change the diameter of the circle?

Let me restate it: for a given lens, the distance to the sensor does not change, no matter what camera you mount it on (given that it is mounted correctly). An image from any given lens is the same brightness on a micro 4/3 sensor, as it is on a Super 35 sensor, as it is on a FF sensor. Same brightness.

Aki_Hartikainen
03-18-2012, 02:15 PM
Same relative brightness. If the smaller film or sensor can capture 10 photons and not 40, the output does not magically turn from 10 photons to 40 photons. You amplify to get the same brightness. Can we agree on this? Because if we can not agree on this, we have a lot to explain to Mr. Einstein.

To crop is to magnify. When you crop and magnify, you will lose light no matter what. But then you compensate. In Photoshop this happens fully automatic, you crop an image for ten pixels and ten photons and enlarge it to full screen, you now use more display power per pixel for same brightness. With film projectors, not so automatic. Generally more candle power is needed for smaller film size or lens must be changed.

True, I made the image above by changing the register distance, but it does not change the principle. It only illustrates what happens when you crop and magnify. Had the lens had a different lens element for the smaller light circle, more brightness would have come from the same distance with the same aperture. The m4/3 lenses have a lot of potential for bright images, but this has not yet fully materialized. It may be difficult to produce very sharp lenses for smaller but brighter image circle.

nothing
03-18-2012, 07:53 PM
If you change the magnification of a lens by expanding or contracting the image circle, you effectively change the focal length of the lens. Without a corresponding change to the aperture, the f-stop (focal length divided by aperture) of the lens is altered. Thus you perceive a loss or concentration of light when moving the lens further or closer to the imager plane.

Lenses cannot be mounted at any arbitrary distance from the imager, however, they must be mounted at a specific distance in order to focus correctly. Thus an f2.8 lens is an f2.8 lens on any camera it is correctly mounted on, regardless of imager size.

Zephyrnoid
03-18-2012, 08:30 PM
If you change the magnification of a lens by expanding or contracting the image circle, you effectively change the focal length of the lens. Without a corresponding change to the aperture, the f-stop (focal length divided by aperture) of the lens is altered. Thus you perceive a loss or concentration of light when moving the lens further or closer to the imager plane.

Lenses cannot be mounted at any arbitrary distance from the imager, however, they must be mounted at a specific distance in order to focus correctly. Thus an f2.8 lens is an f2.8 lens on any camera it is correctly mounted on, regardless of imager size.

fascinating exposť. allow me to help out in your excellent effort?
- "If you change the magnification of a lens by expanding or contracting the image circle"
No such thing is possible. In the paradigm of > Image < Lens < Object , the focal length is defined here... (http://en.wikipedia.org/wiki/Focal_length)
It's a number in mm that is calculated as the distance from the 'normal' of the lens, where the light rays, converge and then cross over to the image plane. The image circle is the image that is thus produced. The effective 'usable image' is the area that is cropped by a mask that sits behind the camera's lens mount. The Image circle itself cannot be expanded or contracted, just the cropping is. You do effectively change the focal length of a lens by say...adding extention tubes to the rear mount as this increases the distance between the normal of the lens and the image plane.
- "Without a corresponding change to the aperture, the f-stop (focal length divided by aperture) of the lens is altered."
This line contradicts itself. Aperture is a number that is calculated by dividing the focal length of the lens by the diameter of the iris for that given optic.
- "Lenses cannot be mounted at any arbitrary distance from the imager"
sure they can, with extension tubes. This does change the cropping AND magnification of the Image with a given optic.
- "however, they must be mounted at a specific distance in order to focus correctly."
I think we've dealt with that too.
- "Thus an f2.8 lens is an f2.8 lens on any camera it is correctly mounted on, regardless of imager size"
correctly mounted is sort of meaningless and image circle has also been dealt with.
What are you trying to say?

nothing
03-18-2012, 08:50 PM
fascinating exposť. allow me to help out in your excellent effort?
- "If you change the magnification of a lens by expanding or contracting the image circle"
No such thing is possible.
Ever heard of a zoom lens?


You do effectively change the focal length of a lens by say...adding extention tubes to the rear mount as this increases the distance between the normal of the lens and the image plane.
I thought you just said that this wasn't possible? And have you ever tried to focus to infinity when mounted on an extension tube? That is what I mean by not corrected mounted - not able to be used normally.


- "Without a corresponding change to the aperture, the f-stop (focal length divided by aperture) of the lens is altered."
This line contradicts itself. Aperture is a number that is calculated by dividing the focal length of the lens by the diameter of the iris for that given optic.
No, aperture merely means a hole of a certain size. The f-stop number is what is calculated by dividing focal length and iris diameter (ie the APERTURE).


- "Lenses cannot be mounted at any arbitrary distance from the imager"
sure they can, with extension tubes. This does change the cropping AND magnification of the Image with a given optic.
Again, a lens mounted as such cannot be used normally. What is the point of bringing it up? Besides, extension tubes alter the focal length of a lens, and consequently the f-stop number.


- "however, they must be mounted at a specific distance in order to focus correctly."
I think we've dealt with that too.
Yes, now I have dealt with it here - they cannot be used normally.


- "Thus an f2.8 lens is an f2.8 lens on any camera it is correctly mounted on, regardless of imager size"
correctly mounted is sort of meaningless
Correctly mounted means mounted at the proper flange distance and hence able to be used normally - focusing to infinity and close focus as designed.


and image circle has also been dealt with.
What are you trying to say?

I don't understand your point at all. Are you trying to agree with Aki? Although we've already gone way off-topic as is, your post doesn't seem to have much relevance at all and it just comes across as disagreeing with everything I say just to disagree.

Aki_Hartikainen
03-18-2012, 09:08 PM
The lens is f2.8 on any camera it is installed on, but any camera is not the same. That's why it is called a system camera. It is a system that consists of the lens and the camera. The area of the imaging device plays a role in the brightness of the image. Even if relative brightness is the same on the surface of the imaging device, amount of total brightness will not be. 10 captured photons are not as bright as 40 captured photons. That would be against laws of physics. We need to amplify and adjust, which can be well done as was stated many times already.

You are being ignorant of the camera part of the system and insist on focusing on the lens only, which is not enough to determine the brightness of the final image.

nothing
03-18-2012, 09:19 PM
You are being ignorant of the camera part of the system and insist on focusing on the lens only, which is not enough to determine the brightness of the final image.

So explain to us what you think the camera is doing please.

I can tell you that a 16mm camera loaded with any particular film and a 35mm camera loaded with the exact same film, with the exact same lens set to the same f-stop, shooting the exact same test chart (or even a plain wall) under the exact same lighting, will both produce the exact same image density on the negative. That is a fact. How do you explain that?

Aki_Hartikainen
03-18-2012, 09:27 PM
Surely any film size will expose and develop to the same density behind a certain lens.

But when we had to produce similar sized images for viewing, and only had certain amount of wattage or developer activity to spare, final brightness for images will be different from different film sizes. And this situation is the same when comparing full frame and cropped frame digital cameras. Now the development will happen electronically and digitally inside the camera, but the principle remains the same. The smaller image has to be magnified more, thus needing either more wattage or more developing for the same brightness.

nothing
03-18-2012, 09:32 PM
Optically 50 mm f2 lens for full size camera becomes the equivalent of 100 mm f4 on a 2x crop camera


Surely any film size will expose and develop to the same density behind a certain lens.

These two statements contradict each other. Which are you saying is correct?

Aki_Hartikainen
03-18-2012, 09:40 PM
They do not contradict at all. You crop the sensor, you will take a smaller image. But we are going to view the images at the same size. The smaller image has to be magnified more, and that's what happens inside the camera. You crop the image, you will have to magnify more and spare more wattage. More magnification means more wattage or development required for similar viewing brightness. We will view the images from a certain sized display, and not the negatives.

You crop the sensor or film, you reduce light gathering power for the system. Brightness of the final image will suffer, unless adjusted and amplified.

Aki_Hartikainen
03-18-2012, 09:48 PM
If you put a smaller window in your home, is the brightness inside going to remain the same regardless of what's in front of the window? The window is the camera sensor or film size and the indoor is your final image that you view. Sensor or film is camera's window to the world. :smile:

I am sure we are beginning to get on the same page now.

Aki_Hartikainen
03-18-2012, 09:56 PM
If you put a 50 mm f2 lens in front of the window in your home, and all of the light comes through the lens and the window, you will get certain image brightness in the house. Right? So you reduce the size of the window to one quarter and the lens remains the same. What kind of brightness can you expect inside your home?

That would be the equivalent of 50 mm f4. But now from the smaller window you also have reduced field of view. What does this mean? Your 1/4 window made your image the equivalent of 100 mm f4. It was the window, not the lens that caused this.

At least your depth of field remains the same regardless of the size of the window.

nothing
03-18-2012, 09:58 PM
Nnot a relevant example - you aren't lighting a whole interior of a house with a lens, you are just illuminating a certain area of the sensor - which will still be as bright whether you crop the rest of the illumination away or not. This is assuming you are talking about direct light through the window - if you are talking about indirect light, then the window size is more analogous to the aperture than the sensor size.

Aki_Hartikainen
03-18-2012, 10:08 PM
We are lighting the whole house through a window, that has a lens in front of it. If you resize the window, all of the aforementioned will start to have an impact on the indoor brightness and field of view. Now we are considering the whole system, and not just one part of it.

Aki_Hartikainen
03-18-2012, 10:18 PM
This is why I tell kids to take physics and chemistry in college, instead of photography or videography. But they won't listen.

nothing
03-18-2012, 10:21 PM
We are lighting the whole house through a window...

Absolutely irrelevant example then. No relation to a camera, which isn't concerned with the illumination on side walls, only on the imager plane.

deturbanator
03-18-2012, 10:22 PM
How about this for an example.

You have 3 things when you are taking a picture: the light source, the lens (in this case we specifically talk about the aperture), and finally the sensor.

As an analogy, we have a house, with a sunny scene outside through the window, and people inside looking outside. The scene is our light source. The window is our lens, and in this case we have a fixed window size, relating to the fixed aperture when talking about the tamron on two different cameras. Finally we describe our different sized sensors by changing the number of people who are looking outside.

Let's say every eye is a pixel. Well the cannon body with its APS-C sensor will have more photosensitive pixels than the gh2 and it's micro-four thirds sensor. Even for the sake of this argument, we can say that two cameras with the same sensor size but different pixel counts can be represented by this analogy.

I think that we can all agree that as long as the scene and the window stay the same, the light coming into the room stays the same aswell. Now it is all about the perception of the light by the people in the room. We can conclude that no matter how many eyes are looking outside, they all see the same image at the same brightness, and that the number of people looking outside does not effect the brightness of the scene. That is to say that if 1 person looked outside vs 100 people looked outside, the 100 people would NOT have seen the scene 100x less brightly. If this was the case, I would argue we all should have a very hard time seeing anything at concerts, plays, or any group gatherings.

Since light essentially travels in rays, any light that goes to one person's eye gets trapped and lost to our eye, but no other eye will use these particular rays to form their image. Similarly, having a camera with a bigger or smaller sensor, or a higher or lower pixel count will NOT affect the brightness of the captured image. Assuming the pixels are just as light sensitive from one sensor to the other, there will be NO difference in the brightness.

Finally we must address this very subtle assumption. Not all pixels are created equal. For example we know for fact that the GH2 is in general darker than the GH1, but this is not because the light hitting the sensor changed at all in brightness, it is because the actual pixels themselves are not as sensitive, or are calibrated differently. What does this mean about the argument? Well, the tamron at 2.8 on a cannon at iso 100 and shutter speed 60 COULD be brighter than the GH2 at all the same settings, but this would not be a result of the size of the sensor, but rather the sensitivity of the sensor. So it would be just as fair to think that it is possible the GH2 will actually produce a brighter image.

And to the person who argued about the light having to travel a longer distance, yes this will in fact lower the brightness of the light, but when we are talking about an inch at most of space between the back element and the sensor, the difference in light intensity would be incredibly negligible. If you had one camera mount the lens a quarter mile away from the sensor, and one camera mount the lens an inch from the sensor, you would certainly tell a difference then, but from a cannon or nikon distance away to a microfour thirds, the difference is more than negligible.

If this was at all unclear, ask away. I will be happy to elaborate further.

By the way i'm a physics student at a top tier univeristy.

Aki_Hartikainen
03-18-2012, 10:28 PM
Absolutely irrelevant example then. No relation to a camera, which isn't concerned with the illumination on side walls, only on the imager plane.

Take a solar panel then. Is a quarter sized solar panel going to produce the same brightness as full size panel, when you hook a lamp on it?

deturbanator
03-18-2012, 10:54 PM
A solar panel will produce no brightness because that is not what it does. It absorbs energy. And in this case the size makes a huge difference in the amount of energy gathered. However the energy captured per unit area will not change, and this is proportional to the brightness of the image if we are making comparisons to the camera sensor.

Aki_Hartikainen
03-18-2012, 11:53 PM
A solar panel will absolutely produce brightness, when you hook a lamp or display to it. The bigger the panel, the brighter the lamp or display. What is a camera if not a solar panel with a lamp or display attached to it? What is it?

deturbanator
03-19-2012, 01:03 AM
I really hope you are joking. A solar panel converts the energy stored in light, and converts it to energy stored in electricity. This energy is then converted from electrical energy to whatever you hook it up to. Now when you say it produces brightness you are clearly mistaken. For example I could just as easily hook up a dim light to the solar panel as I could hook up a very bright light. Or lets say that the solar panel stores this energy in a battery. Then for the same amount of energy I could hook up a bright light for a short period of time or a dim light for a long period of time.

The way the cmos sensor works is much different than the way a solar panel collects energy.
http://en.wikipedia.org/wiki/CMOS

EITHER WAY, as I said before, it is not about the TOTAL light collected, but the light collected per area.
Take classic film. If you have a giant sheet of photosensitive paper versus a small sheet of photosensitive paper, any exposure to the film will be the same when exposed to the same light source. You would NOT expose the larger film to less light to get the same exposure.

Aki_Hartikainen
03-19-2012, 01:09 AM
EITHER WAY, as I said before, it is not about the TOTAL light collected, but the light collected per area.

Only if we insist on ignoring the camera and display parts of the system.

We do not view the images at the size they were filmed. They have to be re-sized for viewing. The smaller image has to be re-sized more. Now what do you suggest is required to re-size? Yes, wattage. More re-size means more wattage. Take a projector and move it away from the screen. Is the re-sized image still as bright with the same wattage?

deturbanator
03-19-2012, 01:22 AM
You are making many analogies that are very different/untrue. Projectors certainly will certainly become less bright when moved away from the screen because the intensity of the light is inversely proportional to the distance squared of the image formation to the light source.

Go into photoshop and resize an image. Does it become brighter? I would expect not. This is what a sensor does, and it is nothing like how a projector acts.

Here is but another example as to show the whole relationship to the light collected per area. We all know that the gh2 uses a much bigger sensor to produce a 1080p video. Like I said, it resizes the image in some way similar to how we would resize images (in such a way to reduce the causes of moire and aliasing). However the GH2 has an EX-TELE mode where it will digitally zoom in. In this mode, it uses exactly 1920x1080 pixels located in the center of the camera to record the video an it then does not get resized at all when recording the footage. Does the brightness of the footage decrease when this happens? Nope. Should we expect it to? Well lets look at the light captured per unit area. We are exposing to the exact same light source so lets call this amount L. To calculate the light captured per unit area, we do L/A. Now when using the whole sensor, and for simplicity lets say the GH2 sensor is 4x(1920x1080) pixels, we will have 4 times the area to capture light, and because of it we will have 4 times the amount of light captured. However each individual pixel in the big sensor or small sensor version will capture the same amount of light. The light per unit area is the same.

I am not "debating" you as much as I am just letting you know how it really is. If sensor size made a difference, then EX-TELE mode would cause your image to be VERY dark.

Aki_Hartikainen
03-19-2012, 01:44 AM
Can you explain why in Photoshop cropping does not make the image dimmer when enlarged to full screen unlike projector that was moved away from the screen?

Because you are using more watts per pixel. You just changed the relative brightness or light per area, and that's what you have insisted for several pages must not happen. But it happened anyway. And that is exactly what happens inside the camera. The camera develops the image constantly unbeknownst to us. Various amplifications are applied, and we don't need to care about it much. The camera engineers have made sure same brightness comes from EX-TELE mode as in normal mode.

If you were an astronomer, you would get it. The whole system has to be considered for desired end brightness. You change one part of a system, you need to compensate for it. You don't need to compansate in Photoshop, because the software and the display do that for you.

deturbanator
03-19-2012, 02:08 AM
I do not need to be an astronomer to have common sense. As I have said before I am a physics student. I have a pretty good grasp of this concept.
You are comparing digital screens to light projections, and they are not the same. When you look at a projector, you really have a single light source, which is the bulb in the projector that projects the image. since this is the single light source, of course when you move the projector back and forth, you brighten or dim the image. This is expected for any light source of this type.

However a screen is composed of a bunch of light emitting pixels. When you digitally resize an image, you are taking a certain area of pixels, and turning that into one pixel. Same can be said the other way around. The brightness of the image is in no way determined by the size of the picture, but the brightness of the display, or how bright each individual pixel is. For example, we as cinematographers constantly have to worry about calibrating our monitors such that they display similar to where we would be showing our work. If my monitor is really bright and yours isnt, and I sent you a file, I would see the video bright, and you would see the video dim. The size didnt change, but the brightness of the pixels on our monitor did.

EDIT: for clarification. The digital picture is what we are resizing. The digital picture is just information the computer reads and converts into display data. When we make 4 pixels into 1 for resizing, we are not doing a display resizing, but a data resizing. The display is just told what color to output and it outputs that color at the brightness that is predetermined for the screen. We are really just adjusting colors and number of data points when resizing a digital image. END EDIT

The main problem with your argument is the whole light per area thing again. When you choose a projector at a certain wattage, you are selecting the energy BEFORE you select the area. Of course when you change the area, and keep the energy the same, the intensity will decrease or increase. However, on a digital screen, we do not set the energy or the area. Rather we set the energy per area. If my screen is 2x as large as yours, and it is just as bright, and uses the same type of pixels and stuff, then I will be using 2x the energy. As I scale up, my energy usage does as well. But don't confuse a sensor with a monitor. They are very different, and basically act in opposite ways when it comes to light.

Just out of curiosity what is your age and education, and why do you feel so confident in what you are saying? Just out of gut feeling? Cause you are clearly mistaken. Photoshop does not "compansate for you"

AND FINALLY, to prove this all to your self, if your camera automatically adjusted the image for you, then why do you have the full iso range in EX-TELE mode. Obviously the only thing that can be adjusted when doing this cropped mode is the ISO, but you clearly get the full range still. There is no magic going on in the background. Just simple physics.

deturbanator
03-19-2012, 02:21 AM
To further illustrate you do not know what you are talking about take this quote of yours:

If there is something to consider in this is that the F-rating for the lens does not determine it's brightness. It only determines the maximum aperture / focal length ratio. Brightness is determined by the size of the light circle that the lens outputs. The smaller the light circle, the more focused is the light, thus increased intensity and brighter lens.

When you say the smaller the light circle the more focused the light, you are referring to something like a magnifying glass and the sun. But this is not what is happening. The light is already focused when you adjust the focus of the lens. By stopping down the aperture, you are not "focusing the image" just blocking light from passing through. If stopping down focused the image, then it would be impossible to make an f1.8 lens in focus right? yet we do so every day. You might argue that images become more in focus when you stop it down, and you would be wrong. Images become sharper, not more in focus. Sharpness is something different than focus, and is a pretty complicated concept. Focus ONLY has to do with the lens and their focal lengths and distances from one another.

Seriously, stop spreading false information. It hurts the community.

Aki_Hartikainen
03-19-2012, 02:34 AM
I do not need to be an astronomer to have common sense. As I have said before I am a physics student. I have a pretty good grasp of this concept.
You are comparing digital screens to light projections, and they are not the same.

They are the same. You put 10 photons in, you won't get 40 out without doing something in both optics and electronics. This something happens in electronic devices unbeknownst to you, but the underlying principles are the same as with optical devices. I studied optics and physics in university for two years.

deturbanator
03-19-2012, 02:47 AM
At this point, I will probably just let you live in your world with your own laws of physics.
While you studied these topics, you evidently do not have a strong grasp of the ideas behind them.

The biggest thing you as missing is the conversion of light to digital memory. We are not taking photons, and using the same activation energy used in the sensor to display on the screen. We are using the energy of the photon to activate a pixel, and then using energy completely from the battery, we then convert the activation of the pixel into digital data. And the screen reads the digital data to then produce a light using the energy from the battery. This conservation of photons or whatever does not apply because you are not including all the energy that comes from the battery.

The digital data is just a mapping of colors to locations. The display can display any color at any brightness at any size because it is completely arbitrary to the amount of brightness used to create the data. This is all ISO stuff.

50201

EDIT: and projectors and digital screens are clearly not the same. Projectors, again, have one light source, and they are put a distance away from where the image is formed. Digital monitors form the images right where the light is is being made, and use millions of light sources. Why do you think you never have to "focus" and a digital screen?

Aki_Hartikainen
03-19-2012, 03:55 AM
Inside the camera circuits keep constantly developing the image to the proper brightness regardless of camera sensor size or operating mode as determined with high precision by extremely skilled engineers in Japan and Germany. That this happens unbeknownst to us is no reason to ignore it. If we have only 1/4 sensor area, the sensor must be four times more sensitive to light for same brightness, all else being equal. If you squeeze 16 mp photosites from full frame on 1/4 frame, that should do it. Is the lens now capable of transmitting same amount of light for 1/4 area?

The lenses were designed for full frame photosite density, not four times the full frame density.

Aki_Hartikainen
03-19-2012, 05:16 AM
If you were an astronomer, you would instantly be like "whaat... 1/4 sensor area? You realize we can not capture all of the photons now? And who is going to pay for the liquid nitrogen to cool down the smaller sensor for lower noise floor and increased dynamic range..." :smile:

colin rowe
03-19-2012, 07:53 AM
Hi!

I had a chance to play with the Nikon 17-55 2.8 a couple of days ago. I don't have the money right now to buy it so I am lookin for the next best thing that I can afford.. Reading a lot of reviews and the Tamron 17-50 non VC looks like a steal for the money! I'm looking for the one that's 67mm in the front since that one is non-VC.

Does this lens preform good on the GH2? I understand that it will not be as good as the Nikon but judging what people say it's not that different (besides the build quality).

Comparing this lens with old Nikon E primes such as 28mm 2.8, 50mm 1.8, and 100m f 2.8, how good is the Tamron?
To get back to the original post. Yes the Tamron is a very good lens for video, it wont dissapoint.
As for the overly drawn out discussion on technical issues, give it a rest guys, do you really think anyone gives a toss

Admir
03-19-2012, 09:28 AM
Aw man I just wanted to hear your thoughts about the darn lens not to start a fight... Thank you for explaining stuff and taking your time but please use the personal messeage function to solve your problems with each other. Or at least make a new thread with tests that prooves whos wrong and right instead of attacking each other...

GarageBoy
03-19-2012, 12:04 PM
Think about a 4x5 camera with a standard lens on it (~150mm) F5.6
Expose for EV 11 (1/60 sec)

Take a 35mm piece crop of that piece of film
You should get the same results if you had a 150mm lens at F5.6 mounted on a 35mm SLR...

Aki_Hartikainen
03-19-2012, 12:23 PM
Think about a 4x5 camera with a standard lens on it (~150mm) F5.6
Expose for EV 11 (1/60 sec)

Take a 35mm piece crop of that piece of film
You should get the same results if you had a 150mm lens at F5.6 mounted on a 35mm SLR...

True, but we will not be viewing the negatives. We will be viewing different film sizes magnified to the same size. The other film size has to be magnified more than the other. If there is no power increase when magnifying the smaller film, it will be seen as dimmer. This power increase, more watts per pixel, will happen completely without our intervention in a LCD display.

For viewing the different film sizes at the same size and at the same relative brightness would mean the smaller film would need more exposure while shooting. If the smaller film was 1/4 area of the larger film, for the same viewing size and same relative brightness without power increase the smaller film would need +2 f-stops more light to be seen equally bright at the same size after magnification.

Take a projector and put a 35 mm film in it. For certain image size you will get certain brightness. Insert 16 mm film in the projector and adjust the size for the same. You will need to pull the projector away from the screen to magnify image. Without power increase in the projector the 16 mm negative will have to have been exposed more to be seen equally bright at the same size.

Aki_Hartikainen
03-19-2012, 01:17 PM
This same would apply if you tried to make hard copies from film negatives. Smaller negative size will require more exposure for the same paper size all else being equal. I can see that this concept is today completely ignored in media and video and photography schools.

nothing
03-19-2012, 08:42 PM
For viewing the different film sizes at the same size and at the same relative brightness would mean the smaller film would need more exposure while shooting.

Wrong. You are ignoring the proper exposure range of the film and will overexpose if you do that.

You are confusing completely separate processes. Enlarging during printing or viewing has nothing at all to do with proper exposure during shooting or the f-stop of the taking lens. First you expose the negative. Then, later, you enlarge - a completely separate process that depends itself on a PROPERLY exposed negative. By your methods you will overexpose said negative and have to compensate in printing or color correction - but even then you may not be able to recover the highlights.

The results are worse with digital.

Aki_Hartikainen
03-19-2012, 08:48 PM
You are confusing completely seperate concepts.

Somebody is confused, but not me.


Wrong. You could change the lens instead of moving the projector and get the same size and brightness image with the same wattage.

Yes I could. But that was not the point, was it? Now you are changing the lens to a different one to get the same image brightness. But it all started when we were using the same lens, if I remember correctly.

nothing
03-19-2012, 08:53 PM
Yes I could. But that was not the point, was it? Now you are changing the lens to a different one to get the same image brightness. But it all started when we were using the same lens, if I remember correctly.

I am talking about changing the focal length of the lens, not the f-stop. I thought that was obvious, I guess it wasn't.

My comments about projectors have been deleted as projectors are not my expertise, cameras are. I have been drawn way off topic in this thread.

deturbanator
03-19-2012, 09:11 PM
Don't waste your breath with him. Aki clearly has no idea what he is talking about.
"unbeknownst" to all of us, digital camera manufactures do all this crazy math and physics in the background to make everything just "work"

Its almost like magic.

Aki_Hartikainen
03-19-2012, 11:23 PM
I think it is a bit more magical to suggest you put 10 photons in and 40 comes out from every camera just like that. I went to astronomy class and this was the 1st concept of the first lecture: you put something in, don't expect more to come out.

deturbanator
03-19-2012, 11:53 PM
Okay smarty, so you you change the iso on your camera. What was once a dark scene is now brighter. You put in 1 photon, you get more than one out. Blahblah shitty example just to counter yours. You are talking about conservative systems which this isnt. And you are talking about putting photons in and getting them out likethey are the same photons you are seeing. This is a digital camera without a mirror. The only thing you ever see from the camera is a digital image whether it be from the evf or the screen. It is digital. Your stupid laws do not apply in this world. Seriously go make sure you are sterilized so your kids wont have to suffer through your nonesense.

Aki_Hartikainen
03-20-2012, 12:11 AM
If a telephoto lens that sees 10 photons is dimmer than normal lens that sees 40 photons, why would a crop sensor that sees 10 photons suddenly be as bright as a sensor that can see 40 photons? Because it won't. It is of no use to speak about registers and mapping values and stuff, if the most fundamental and basic law of optics and electronics can not be acknowledged.

What is nonsense in that?

nothing
03-20-2012, 07:08 AM
If a telephoto lens that sees 10 photons is dimmer than normal lens that sees 40 photons...

If said lenses have the same stop, then neither is dimmer.

Admir
03-20-2012, 07:09 AM
Ok so I got the tamron Today. Here my first impressions:

Pros:
Really solid! It feels like a expensive lens, I did expect something a bit more flimsy but this feels like a grenade in the hand!
Sharp! Even at 2.8 I get quite sharp images.
The focus DOES stay the same while zooming, that's fantastic!
Smooth focuswheel, not to stiff, not to easy, just perfect!

Cons:
Somewhat filmsy zoom wheel, it has a freespace of a couple of milimeters that comes into play before the actual zoom starts.
Focus throw is huge, this will take some time to get used to.
Maybe it's just me, but when zooming the aperture changes, so the image can be slightly darker on 17mm, while on 35 it looks like it gives a bit more light... This could be because of the nikon adapter I'm using since it isn't totaly stiff when turning the focus maybe... EDIT: It was the nikon adapter that was loose, I managed to tighten the mount now it's all good!

All in all a perfect lens, and for 70 dollars (sine the focus motor is broken in it) it a steal! It looks like brand new and came with all the original papers, box, and sunhood... Sweet deal!

DrDave
03-20-2012, 11:00 AM
A sensor is not bright, it is dark. This is the essential flaw in all of this. Black silicon absorbs light and is dark. It can be used for solar cells or camera sensors.
Lenses transmit iight. Monitors emit light, and so on.

If you had one photon, one lens and two sensors, the photon would probably but not certainly go through the lens and would land on the sensor that you measured, but not on the sensor you did not measure.
However, neither sensor would be brighter, as the sensors absorb light. If they were brighter, they would be mirrors.
The sensor then has a sensitivity factor. Just as a solar cell converts say 15% of the light to energy, a sensor will convert a percentage of the light to (eventually) a digital signal. However, this is where the statement "in-out" does not hold up. If it did, we could have 100 percent efficiency. which we don't. Most of those photons are simply absorbed.
They are stuck in the LaBrea tarpits of video history.
Light is not just a stream of photons that leaves the train station in SF and arrives in LaBrea. Things happen along the way, for example they are scattered, absorbed, reflected, etc.

Here is the thing. If you design a simple experiment, like the one with the business card, and use controls, you will eventually probably--but not certainly--discover that your measurements are wrong and that actually the basic principles of optics are still true. However, if in fact you are correct, you will for sure gain scientific recognition for your experiment. So I would encourage you to get some basic measuring tools and see what is really going on with the lenses and the sensors: Use real lenses and real sensors, and scientific controls. After you have done the experiment, make a video of it and post it on youtube. So if you think a 50/F2 becomes a 100 F/4, make a video of that. Keep it simple.

Cropping:
Let's say you take a photograph and crop it with scissors. Is the smaller photograph dimmer? If you measure the amount of light at the surface, you would think so. Measure it, you will see it reflects less total light. Measure different spots on the photograph and you will get different readings.

Here's the thing. The photograph is not actually emitting light. It is both absorbing and reflecting light. These are not the same. And if you had a black photograph, a larger one would emit the same light, more or less, as a cropped one, since they aren't emitting light. If you turned the light off in the room, the black photo would be the same as the white photo.
Digital cropping: the light comes from the monitor. If you turn the monitor off, they will both look the same.

Inverse square law
If you move the light source farther away, it will be dimmer. If it were just a "number" of photons, you might think, hey, forty left, forty arrived, there would be no light falloff. You can test that and see for yourself. Now lets say you bolt an F2 on a film camera and then on an M43 camera. You will need an adapter which moves the lens farther away. The flange distance will change the actual distance from the light source to the sensor. And the "brightness" will change. The larger the flange, the larger the distance. So you have to make some fairly complex calculations. And did all those photons arrive? Did they all travel in a straight line?
Try to measure the photons and you will see that they are unpredictable, to say the least. Look forward to your experiment and video.

Concentrating the light
It is possible to do this. There are special lenses for telescopes that do exactly that, and there is a whole branch of optics that works on concentrators of various types. You could add one of these lenses to an F2 and have it then be an f1.4

Converting lenses with smaller sensors
If what you say is true, you could take a F1.4 lens from a full frame camera and bolt it on to a P&S camera and have the world's fastest lens. You can try it and see if it works. You can buy a Canon 3G for $10 or I will even give you mine. It takes adapters. The ultimate LL cam. I knew I kept it for a reason.


PS In my astronomy and astrophysics classes, no one ever mentioned photons in photons out on the first day.

DrDave
03-20-2012, 12:00 PM
Ok so I got the tamron Today. Here my first impressions:

Pros:
Really solid! It feels like a expensive lens, I did expect something a bit more flimsy but this feels like a grenade in the hand!
Sharp! Even at 2.8 I get quite sharp images.
The focus DOES stay the same while zooming, that's fantastic!
Smooth focuswheel, not to stiff, not to easy, just perfect!

Cons:
Somewhat filmsy zoom wheel, it has a freespace of a couple of milimeters that comes into play before the actual zoom starts.
Focus throw is huge, this will take some time to get used to.
Maybe it's just me, but when zooming the apperture changes, so the image can be slightly darker on 17mm, while on 35 it looks like it gives a bit more light... This could be because of the nikon adapter I'm using since it isn't totaly stiff when turning the focus maybe...

All in all a perfect lens, and for 70 dollars (sine the focus motor is broken in it) it a steal! It looks like brand new and came with all the original papers, box, and sunhood... Sweet deal!

If you have some comparisons you can post that would be very helpful. I would be interested in a lens that is sharp wide open. Maybe shoot some examples wide open and stopped down to F4. Tx.

Aki_Hartikainen
03-21-2012, 12:59 AM
Think of the sensor or film as the aperture for the camera. The iris is the aperture for the lens. Both follow the exact same area laws no doubt about it. If you insist on considering one aperture only for the system, you will not be able to determine the final brightness or required amplification.

deturbanator
03-21-2012, 01:32 AM
Think of the sensor or film as the aperture for the camera. The iris is the aperture for the lens. Both follow the exact same area laws no doubt about it. If you insist on considering one aperture only for the system, you will not be able to determine the final brightness or required amplification.

Okay, so we have found the root of the problem. The sensor is in no way like the apeture for the camera. At all. Ever. Period.
It has no properties like the apeture in the lens in any way shape or form. If such a property exists show me on wikipedia or any trustworthy source besides yourself.

In the camera system, there is one, and only one, apeture like object in the camera. And that is the apeture in the lens controlled by the apeture blades. End of story.

This can be easily proven or I could go on any forum or community in the world and they would agree.
Your concept of the camera is greatly mistaken.

Aki_Hartikainen
03-21-2012, 01:43 AM
Your concept of the camera is greatly mistaken.

It is a concept of physics. I did not invent it. The lens gets dimmer because you reduce the area. It makes no difference from physics point of view whether you reduce the area in the lens or in the camera.

Same end result. Loss of brightness.

DrDave
03-21-2012, 09:39 AM
"Think of the sensor or film as the aperture for the camera. The iris is the aperture for the lens. Both follow the exact same area laws no doubt about it."
This is so cool because it means that black does not exist.

deturbanator
03-21-2012, 10:45 AM
It is a concept of physics. I did not invent it. The lens gets dimmer because you reduce the area. It makes no difference from physics point of view whether you reduce the area in the lens or in the camera.

Same end result. Loss of brightness.
As someone with no concept of physics, it must be very easy for you to say that.

Halsu
03-22-2012, 08:30 AM
As someone with no concept of physics, it must be very easy for you to say that.

Just a heads up, we discussed this exact same thing on a Finnish video forum with Aki for dozens of pages - and found out that no amount of explanations, demonstrations or other proof will make any difference (unless the discussion degrading to Ad Hominem attacks by him is considered a difference). Regardless of what you say, he will still be utterly oblivious to the fact that he is wrong and insist that the ones at error are everyone else...

mr.coffee
03-22-2012, 08:53 AM
not sure where this thread has gone, but i recently bought the tamron 17-50 2.8 [nikon mount]
honestly i'm not really loving it. the zoom feels stiff to me, probably because of the motor[when its used on a nikon]
the focus ring is totally loose, as in, theres too much play on it. One little accidental nudge and you'll have to refocus.
I think i'll sell it and look for another zoom, although at this point, i'm not sure what to get [needed for video]
Hope this helps!
best
J-P