02-18-2011, 08:12 PM
[quote name='Lomskij' timestamp='1298054614' post='6230']
Hm. I guess you should have mentioned that ISO is upped only if the pixel pitch is smaller, not because the actual sensor is smaller.
Also I've noticed that you're mixing field of view and focal length - they're not the same. A lens with focal length equal to 50mm and mounted on FF sensor will have horizontal FOV of around 40 degrees. Mounted on ASP-C sensor, the 1.5x crop factor will effectively reduce the horizontal FOV to 27 degrees, which is roughly equivalent to 75mm lens mounted on FF. What I'm trying to say is that FOV is inversely proportional to focal length, therefore you have to multiply by the crop factor, not divide.
[/quote]
Boy, what a confused mess.... Where to start.
ISO is meaningless. That is the main point. Just a 2nd amplification to an unknown amount of amplification.
About pixel pitch... it has NOTHING to do with anything. The whole sensor collects light, the whole sensor makes an image. It is really rather useless to look at 1 pixel at a time.
In case you still want to do that:
If the big and the small sensor have the same amount of sensels, then the bigger sensels will collect more light, the FF ones.
If the sensels of the big one are smaller in a meaningful way (and the pixel pitch is smaller in the same meaningful way), then that means that the pixels in the image will be a lot smaller too, so any noise that would be "gained" per pixel falls away again in similar sized prints.
So, no matter how you look at it, same size pixel or same amount of pixels, the image of the FF sensor (providing we are talking about similar generation tech. for both sensors) will always have about a stop and a bit advantage noise wise (and "ISO WISE").
Of course you have to DIVIDE by the crop factor.
If you use a 50mm lens on FF, and you then want to know an equivalent to 50mm on APS-C (35mm).
I see I made a silly mistake, which I will correct here:
APS-C: 50mm f2. Aperture: 50/2 = 25mm.
FF: 50 / 1.5 = 33.3mm. aperture: 25mm. f-value: 33.3/25= f1.333
There you have it, the corrected numbers. Sorry for erroneously taking 33.33mm for the aperture size.
No where have I confused focal length and field of view. You just might not understand that I meant with (field of view) to indicate that the equivalent focal length is about giving a similar field of view.
Hm. I guess you should have mentioned that ISO is upped only if the pixel pitch is smaller, not because the actual sensor is smaller.
Also I've noticed that you're mixing field of view and focal length - they're not the same. A lens with focal length equal to 50mm and mounted on FF sensor will have horizontal FOV of around 40 degrees. Mounted on ASP-C sensor, the 1.5x crop factor will effectively reduce the horizontal FOV to 27 degrees, which is roughly equivalent to 75mm lens mounted on FF. What I'm trying to say is that FOV is inversely proportional to focal length, therefore you have to multiply by the crop factor, not divide.
[/quote]
Boy, what a confused mess.... Where to start.
ISO is meaningless. That is the main point. Just a 2nd amplification to an unknown amount of amplification.
About pixel pitch... it has NOTHING to do with anything. The whole sensor collects light, the whole sensor makes an image. It is really rather useless to look at 1 pixel at a time.
In case you still want to do that:
If the big and the small sensor have the same amount of sensels, then the bigger sensels will collect more light, the FF ones.
If the sensels of the big one are smaller in a meaningful way (and the pixel pitch is smaller in the same meaningful way), then that means that the pixels in the image will be a lot smaller too, so any noise that would be "gained" per pixel falls away again in similar sized prints.
So, no matter how you look at it, same size pixel or same amount of pixels, the image of the FF sensor (providing we are talking about similar generation tech. for both sensors) will always have about a stop and a bit advantage noise wise (and "ISO WISE").
Of course you have to DIVIDE by the crop factor.
If you use a 50mm lens on FF, and you then want to know an equivalent to 50mm on APS-C (35mm).
I see I made a silly mistake, which I will correct here:
APS-C: 50mm f2. Aperture: 50/2 = 25mm.
FF: 50 / 1.5 = 33.3mm. aperture: 25mm. f-value: 33.3/25= f1.333
There you have it, the corrected numbers. Sorry for erroneously taking 33.33mm for the aperture size.
No where have I confused focal length and field of view. You just might not understand that I meant with (field of view) to indicate that the equivalent focal length is about giving a similar field of view.