09-24-2010, 04:27 AM
[quote name='mst' timestamp='1285223977' post='3127']
Are you sure this was really a aperture error? The Di 60 is a macro lens and it's common for F-mount macro lenses to report the effective aperture to the camera ... which increases with decreasing focus distance. So, what's wide open or f/2.2 at infinity becomes effectively f/2.8 (or even less) at close distances ... where closer starts at around 5 m, IIRC (sorry, can't test at the moment).
-- Markus
[/quote]
Yes, it was an aperture error. The camera shows the correct maximum aperture: f/2 at infinity, f/2.2 starting at 5-10 feet, and so on. But I find no different in bokeh between f/2.2 (which is the widest aperture I can go under the conditions I test under) and f/2.8--the size of the OOF blurs and the "cat-eye" shape are the same. I even see the same vignetting, when I use appropriate exposure compensation. However, when I compare the bokeh of the Tamron 60 at "f/2.8" to my Tokina 50-135 at 60mm f/2.8, the size of OOF highlights in the Tamron is about twice as big as that in the Tamron as in the Tokina. So what I'm saying is that even though the camera is adjusting the aperture based on what it thinks is correct, there's a systematic 2/3 stop discrepancy between what the camera says and what the lens is actually showing. I think that explains why there is (more) underexposure at f/2.2 than at f/2.8.
I'll try to post some test results soon. I don't have a tripod so it won't be as good as it could be, but I think I can demonstrate the main point <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />
Are you sure this was really a aperture error? The Di 60 is a macro lens and it's common for F-mount macro lenses to report the effective aperture to the camera ... which increases with decreasing focus distance. So, what's wide open or f/2.2 at infinity becomes effectively f/2.8 (or even less) at close distances ... where closer starts at around 5 m, IIRC (sorry, can't test at the moment).
-- Markus
[/quote]
Yes, it was an aperture error. The camera shows the correct maximum aperture: f/2 at infinity, f/2.2 starting at 5-10 feet, and so on. But I find no different in bokeh between f/2.2 (which is the widest aperture I can go under the conditions I test under) and f/2.8--the size of the OOF blurs and the "cat-eye" shape are the same. I even see the same vignetting, when I use appropriate exposure compensation. However, when I compare the bokeh of the Tamron 60 at "f/2.8" to my Tokina 50-135 at 60mm f/2.8, the size of OOF highlights in the Tamron is about twice as big as that in the Tamron as in the Tokina. So what I'm saying is that even though the camera is adjusting the aperture based on what it thinks is correct, there's a systematic 2/3 stop discrepancy between what the camera says and what the lens is actually showing. I think that explains why there is (more) underexposure at f/2.2 than at f/2.8.
I'll try to post some test results soon. I don't have a tripod so it won't be as good as it could be, but I think I can demonstrate the main point <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />