12-01-2010, 01:43 PM
[quote name='TheChris' timestamp='1291200372' post='4638']
Exactly the point, gtw. I think that the light loss they measured is indeed the increase of vignetting at larger apertures. A vignetting would decrease the overall sum of light if one does not distinguish the distribution of light within the optical cross section. Optically, if the light in the outer regions of the lens would be lost at wide open aperture, then it must be similar to an additional aperture directly in front of the pixel, something they seem to assume by bringing in the angle at which the light hits the photon buckets. But in this case, the out of focus blur circles wouldn't show an increase in diameter as well when using wide open aperture.
And I guess that the increase in ISO for compensation was not measured but back calculated: they assumed that the amount of recorded photons has to be constant for the photo not to be underexposed, then brought in the measured light loss and calculated, what the "real" ISO must have been for the equation to be valid.
Christian
PS: one last idea: if one uses an old f/1.4 lens and does not program the data into the camera (or uses false data), the camera should not be aware of when to compensate and for how much. I wonder if the images would show the amount of under exposure that has been predicted.
[/quote]
The test is WAY more simple. I would do it if I would have a fast enough prime!
Attach the prime, wide open, to the camera (Canon EOS DSLR). Make a photo. Camera is aware of the lens, and the used aperture.
Press the lens unlock button and turn the lens a bit. Now the electrical contacts are not used anymore. Camera sees NO lens, and has no idea of used aperture. Make a photo.
Compare both photos. My guess: Both photos will be exposed exactly the same.
If my guess turns out to be correct: Articles are bullshit.
Simple enough test.
Exactly the point, gtw. I think that the light loss they measured is indeed the increase of vignetting at larger apertures. A vignetting would decrease the overall sum of light if one does not distinguish the distribution of light within the optical cross section. Optically, if the light in the outer regions of the lens would be lost at wide open aperture, then it must be similar to an additional aperture directly in front of the pixel, something they seem to assume by bringing in the angle at which the light hits the photon buckets. But in this case, the out of focus blur circles wouldn't show an increase in diameter as well when using wide open aperture.
And I guess that the increase in ISO for compensation was not measured but back calculated: they assumed that the amount of recorded photons has to be constant for the photo not to be underexposed, then brought in the measured light loss and calculated, what the "real" ISO must have been for the equation to be valid.
Christian
PS: one last idea: if one uses an old f/1.4 lens and does not program the data into the camera (or uses false data), the camera should not be aware of when to compensate and for how much. I wonder if the images would show the amount of under exposure that has been predicted.
[/quote]
The test is WAY more simple. I would do it if I would have a fast enough prime!
Attach the prime, wide open, to the camera (Canon EOS DSLR). Make a photo. Camera is aware of the lens, and the used aperture.
Press the lens unlock button and turn the lens a bit. Now the electrical contacts are not used anymore. Camera sees NO lens, and has no idea of used aperture. Make a photo.
Compare both photos. My guess: Both photos will be exposed exactly the same.
If my guess turns out to be correct: Articles are bullshit.
Simple enough test.