11-13-2010, 02:03 AM
[quote name='_sem_' timestamp='1289569733' post='4128']
Got no experience with Canon but AFAIK they show the nominal aperture which normally does not change with focus. Older lenses give nominal aperture on Nikon too; I guess you then have to compensate exposure manually (watch the RGB histogram and roll the EC wheel...). I got used to compensating exposure a lot with the Tamron 60 and Nikkor 18-200VR ;( [/quote]
???
The metering system should take care of this, unless these lenses indeed suffered from incorrect exposure problems at specific diaphragms. Stopping down manually should correct this in those cases.
Actually, the aperture doesn't chaneg at all. What changes is the image circle. At 1:1 th eimage circle is 4X as large, area wise, as it is at infinity, which means the saem amount of light is now illuminating 4X the area (of which only an area the size of the sensor is captured), In short, thi smeans 4X less light per area size, and therefore effectively 2 stops loss of light, even if those are not aperture stops.
The only reason why this is often equated to 2 stops is that diffraction also hits 2 stops faster. Unfortunately, popular belief has it that now F/2.8 suddenly becomes F/5.6, which is totally incorrect. It is indeed, as you mention, just the "bellows factor".
BTW, this is no different with IF lenses: the light loss as compared to infinity is purely determined by aereal magnification factor expressed in f-stops.
Kind regards, Wim
Got no experience with Canon but AFAIK they show the nominal aperture which normally does not change with focus. Older lenses give nominal aperture on Nikon too; I guess you then have to compensate exposure manually (watch the RGB histogram and roll the EC wheel...). I got used to compensating exposure a lot with the Tamron 60 and Nikkor 18-200VR ;( [/quote]
???
The metering system should take care of this, unless these lenses indeed suffered from incorrect exposure problems at specific diaphragms. Stopping down manually should correct this in those cases.
Quote:Yes, the whole aperture range is shifted by 2 stops at close focus compared to inf focus. The name "bellows factor" because old macro lenses would shift the whole lens away from the camera to achieve high magnifications just like bellows or extension tubes. With modern IF designs this is not so simple anymore; there still seems to be the same 2 stops difference at 1:1, but there may be a different curve in between; there are also considerable differences among different IF designs regarding what happens to the effective focal length and the working distance at close focus (compare the Nikkor, Tamron and Canon 60mm IF macros).
Actually, the aperture doesn't chaneg at all. What changes is the image circle. At 1:1 th eimage circle is 4X as large, area wise, as it is at infinity, which means the saem amount of light is now illuminating 4X the area (of which only an area the size of the sensor is captured), In short, thi smeans 4X less light per area size, and therefore effectively 2 stops loss of light, even if those are not aperture stops.
The only reason why this is often equated to 2 stops is that diffraction also hits 2 stops faster. Unfortunately, popular belief has it that now F/2.8 suddenly becomes F/5.6, which is totally incorrect. It is indeed, as you mention, just the "bellows factor".
BTW, this is no different with IF lenses: the light loss as compared to infinity is purely determined by aereal magnification factor expressed in f-stops.
Kind regards, Wim
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....