GH2 Worth buying a Tamron 17-50 2.8?

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?
 
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.
 
deturbanator said:
EITHER WAY, as I said before, it is not about the TOTAL light collected, but the light collected per area.
Click to expand...

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?
 
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.
 
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.
 
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.
 
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.
Click to expand...

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.
 
deturbanator said:
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.
Click to expand...

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.
 
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.

YouGetNothing.jpg

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?
 
Last edited:
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.
 
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:
 
Admir said:
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?
Click to expand...
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
 
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...
 
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...
 
GarageBoy said:
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...
Click to expand...

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.
 
Last edited:
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.
 
Aki_Hartikainen said:
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.
Click to expand...

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.
 
Last edited:
nothing said:
You are confusing completely seperate concepts.
Click to expand...

Somebody is confused, but not me.

nothing said:
Wrong. You could change the lens instead of moving the projector and get the same size and brightness image with the same wattage.
Click to expand...

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.
 
Aki_Hartikainen said:
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.
Click to expand...

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.
 
Last edited:
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.
 
You must log in or register to reply here.
Back
Top