GH2 Worth buying a Tamron 17-50 2.8?

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.
 
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.
 
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?
 
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!
 
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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.
 
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Admir said:
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!
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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.
 
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.
 
Aki_Hartikainen said:
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.
Click to expand...

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.
 
deturbanator said:
Your concept of the camera is greatly mistaken.
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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.
 
"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.
 
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.
Click to expand...
As someone with no concept of physics, it must be very easy for you to say that.
 
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deturbanator said:
As someone with no concept of physics, it must be very easy for you to say that.
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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...
 
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
 
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