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02-27-2010, 02:27 PM   #16
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QuoteOriginally posted by causey Quote
I take a photo at 2.8, then one (of the same scene) at 4, then one at 5.6, etc.
The pic taken at 2.8 looks darker then those taken at 4 and 5.6.
OK. does the shutter speed change as you'd expect - exactly half as fast at f/4 as f/2.8, exactly half as fast at f/5.6 as f/4? If so, then this simply indicates the "stops" on the lens aren't 100% accurate. If the shutter speed isn't changing in perfect lock-step with the selected aperture, it would suggest that when you change aperture, you are moving the camera just enough to change where that spot meter is.

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I use spot metering in Av, because I know matrix metering doesn't work with A lenses.
Even if that were true 9which as you've now discovered is not), I still woudln't resort to spot metering unelss you had a very specific reaosn and knew exactly how to deal with this mode. Center weighted, not spot, should be one's general purpose default for lenses that don't support matrix.

02-27-2010, 02:36 PM   #17
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QuoteOriginally posted by causey Quote
In M there is no problem whatsoever...

That's because you have the settings "fixed" and the camera does not change them as it does in Av, Tv or P.
02-27-2010, 02:36 PM   #18
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QuoteOriginally posted by Marc Sabatella Quote
OK. does the shutter speed change as you'd expect - exactly half as fast at f/4 as f/2.8, exactly half as fast at f/5.6 as f/4? If so, then this simply indicates the "stops" on the lens aren't 100% accurate. If the shutter speed isn't changing in perfect lock-step with the selected aperture, it would suggest that when you change aperture, you are moving the camera just enough to change where that spot meter is.
Yes, the shutter speed changes as expected.

QuoteOriginally posted by Marc Sabatella Quote
Even if that were true 9which as you've now discovered is not), I still woudln't resort to spot metering unelss you had a very specific reaosn and knew exactly how to deal with this mode. Center weighted, not spot, should be one's general purpose default for lenses that don't support matrix.
Actually, I was using center weighted metering, not spot, before finding out that A lenses work with matrix. But "spot" came to mind when I was asked about metering. Great benefit for me to learn that I can use A lenses in matrix metering mode! It will spare me some errors.
02-27-2010, 02:40 PM   #19
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QuoteOriginally posted by SpecialK Quote
That's because you have the settings "fixed" and the camera does not change them as it does in Av, Tv or P.
If by "fixed" you mean what I think you mean, then your clarification coincides with my (tentative) explication above. Thank you.

02-27-2010, 11:22 PM   #20
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QuoteOriginally posted by causey Quote
In M there is no problem whatsoever... And the exposure variations don't happen with only one lens, but with five. Perhaps I'm expecting too much consistency--and it's true that the first images (and max. apertures) seem to be the most problematic ones. Anyway, I'll try what you suggested tomorrow. Thank you and all the participants to the thread.
If exposure is completely consistent in M mode when shot against a blank target, then there is no mechanical issue with the aperture coupling or with the shutter speeds.

What you are seeing is variation in metering between exposures. That is the only variable left. Repeat the blank wall test in Av mode.

Steve
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