Originally posted by Lensvision Interesting.
I'm currently following an available light photography course and using my prime M lenses a lot, mostly at 2.8 sometimes at 3.5 (and using a tripod).
With using the green button the pictures become much lighter then when I expose a bit faster.
You are right about this being a K10D thing, I've read about it on several forums.
I think I'm gonna play a bit with the apature setting next week at the course, see what happens
If you are going to play, find a nice uniform grey surface, sidewalk, paved or gravel road, block wall, etc. (when I began photography, I would meter off such a surface, and then just leave the exposure set that way as opposed to carrying a grey card)
using the green button to set shutter speed, take a photo (not just look at metering) of the surface at each apature click.
In a photo editor, look at the histogram, and note the grey scale mean value. (using PSP X2 I can actually select the central portion of the image and get the grey scale value for only the selection, not so sure about other programs.)
Plot this vs F stop (remember F stop is on a log scale)
If you have all settings on neutral (for JPEG) or shoot raw, each F stop is 45 in greyscale, from the range 25-230, and the camera should meter normally in the 110-120 range (I think the actual point is 110)
I have checked each of my lenses this way, using both the *istD and K10D, ISD is perfect, K10D is as I described.
This has led me to believe pentax knows there is a problem probably with light reflecting off the focusing screen, and has compensated for it in software. Someone else reported that they put an *istD screen in, and it metered perfectly with K mounts but then screwed up the AE lenses. Although without data it is only anticdotal, it kind of supports my theory about a software fudge.