Originally posted by stevebrot Lowell Goudge has done quite a bit of testing and recommends replacement of the stock screen with one from a *istD. You might also want to try the foil trick to short the contacts. I have not had much success with it, but my understanding is that you can trick the body into thinking an "A" lens is mounted. You then manually set the aperture on both the body and the lens (Maxwell...correct me if I am wrong here) and the camera will set the appropriate shutter speed in AV or P mode.
Steve
Steve / all interested
The tests I have done are related to the K10, and on the assumption that since the focusing screen is the same, the K20 behaves the same way.
For any one who is serious about understanding how their equipment really works, in terms of exposure, you should at least do a set of controlled tests.
I use a block wall, or paved road, under consistent lighting (usually clear sky)
Using the green button to set exposure, take a set of shots at each apature detent, and then measure the grey scale value for the centra 10% of the frame area using your photo editor (I use PSP X2) perfect exposure, I believe is 110, and you will have a change in greyscale of about 45 (with neutral contrast) for each F stop. This will tell you how your camera meters with each F stop.
You can also do another set of shots, starting with the middle apature (about F8) metered correctly, and then, without changing shutter speed, take shots from wide open to fully stopped down.
Again measure greyscale and check the linearity of exposure. I have found a few lenses that have a slight drift towards over exposure of about 1/2 stop between wide open and minimum apature. Note you may have to do a couple of tests perhaps one metered at f11-16 and the other at F4 to get a full range, as the exposure becomes non linear for greyscale values below about 25 and above 225
If you do these tests for each lens, then you will have a perminant record of lens and camera performance, and then you should always be able to compensate for perfect exposure.