Originally posted by gregmoll I had forgotten that you can set the aperture of an A lens in the camera under Av mode, never use it.
Whether you use the lens in Av mode or not, with an "A" lens, you should definitely use the aperture ring in the "A" position. Otherwise you lose the full time meter reading, you lose flash metering, you lose multi-segment metering, you lose the aperture in the EXIF, etc. You are still welcome to use "M" mode or any other mode you like, but you are definitely better off in all respects leaving the aperture ring in "A". Not to mention the fact that some A-lenses have fragile aperture rings; the less you mess with them, the better.
Since M lenses require M mode, and you seem to value consistency (as I do), I'd recommend simply using M mode all the time. This makes the experience of using M lenses almost identical to using other lenses, except that aperture is set on the lens instead of the body. But the same procedure is followed otherwise.
Do note that one potential difference in metering between M lenses and auto-exposure lenses is that only the latter support multi-segment metering. So you'll potentially get different results for the same scene for that reason alone. Again, in the interest of consistency, I find it most useful to just stay in center-weighted metering all the time.
To address some other points:
- Yes, in theory, stop down metering would yield perfect results - but only if the focus screen was designed for that. It isn't, and more obviously so with the K10D and K20D than the K200D. I actually ran a full series with my M135/3.5 doing a Green button meter reading at each aperture settings, and got exposures that were all within a quarter stop of each other, which is as good a result I get with DA lenses. The K10D and K20D don't do so well here.
- As for the bit about the aperture lever working differently (linear versus quadratic or whatever), I think that has more to do with issues in trying to convert an M lens to work like an A. If you are using the aperture ring at all with a DSLR, the aperture lever is basically just an on/off switch - it isn't proportional to anything. So there shouldn't be any difference between M and A lenses if you are using the aperture ring, as far as my thinking tells me.