01-04-2011, 09:02 AM
[quote name='Brightcolours' timestamp='1294105340' post='5329']
This means that, while the aperture mechanism does not change, the camera and lens together determine a different f-value.
And with Canon... only the user set f-value is being "used", not the "real" aperture.[/quote]
That's just a matter of reporting, isn't it? Canon cameras display the physical aperture, while Nikon cameras show the effective aperture. Of course, both (have to) use the effective aperture for metering.
Anyway: no issue here. The Tamron already starts to report slightly different effective apertures at the distance we measure MTF at, but I made sure to use the correct physical aperture settings. f/22 in the charts is reported as an effective aperture of f/25 by the lens (which means "fully stopped down").
[quote name='Brightcolours' timestamp='1294105340' post='5329']There is something else going on too, "recently" discussed on internet. Wide aperture lenses seem to be too fast for sensors to deal with, and there seems to be tampered with ISO amplifications to make the exposure times match the f-value.[/quote]
Yes, I know, that LL masterpiece ... but the total amount of magnification will probably hardly make any impact in our measurements. And of course, as I understand it, this happens at large apertures, not at f/22.
-- Markus
This means that, while the aperture mechanism does not change, the camera and lens together determine a different f-value.
And with Canon... only the user set f-value is being "used", not the "real" aperture.[/quote]
That's just a matter of reporting, isn't it? Canon cameras display the physical aperture, while Nikon cameras show the effective aperture. Of course, both (have to) use the effective aperture for metering.
Anyway: no issue here. The Tamron already starts to report slightly different effective apertures at the distance we measure MTF at, but I made sure to use the correct physical aperture settings. f/22 in the charts is reported as an effective aperture of f/25 by the lens (which means "fully stopped down").
[quote name='Brightcolours' timestamp='1294105340' post='5329']There is something else going on too, "recently" discussed on internet. Wide aperture lenses seem to be too fast for sensors to deal with, and there seems to be tampered with ISO amplifications to make the exposure times match the f-value.[/quote]
Yes, I know, that LL masterpiece ... but the total amount of magnification will probably hardly make any impact in our measurements. And of course, as I understand it, this happens at large apertures, not at f/22.
-- Markus
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