Focus adustment on a K10D

focus adjustments is not recomended for zoom lenses so i believe i have seen some where,

Focus adjustment works fine for zoom lenses also. What you have seen, I believe, is a warning that zoom lenses don't stay in focus over the zoom range.

The morale being: Focus at the focal length you will be shooting the picture.

Spot on.

And under the correct lighting, the AF will behave differently outside in full sun light then inside under tungsten lights.
Only the K7 does not suffer from this.

Stefan,

Would you please enlighten me on how THAT works?

I would also like to have an explanation as to
- why AF differs in daylight vs. tungsten
- how much is the difference

I have never seen any difference between the sharpness of my images focused by any type of light. I routinely do studio portraits which although lit by flash are focused under tungsten or fluorescent lights. It doesn't seem to be a problem.

Thanks, John. My question was meant as a response to Stefan's statement above, because I thought the difference would be negligible, if any.

I've no idea how much it differs, at least Pentax and others find it enough to make a special sensor to adjust the AF sensor to the light.

The way it works is quite simple, the AF sensor use a prism.
Tungsten light is primarily yellowish so the focus shifts to the front a little.


You could test it with a 50mm f/1.2 or 85mm f/1.4 with those you might notice?
I'm sure the difference would be negligible with slower lenses than the fastest.

Thanks Stefan - it sounds then that we are talking very small differences, that may mean the focus shifts only within the 'depth of field' as it exists for a particular aperture setting? Or have I got that wrong?

No because depth of field is coupled with your focus, so if the AF front focus the depth of field also move more to the front.
I've no idea how much the difference is.

The difference may be small, but at close distance/wide aperture it can be significant, especially if you are trying to adjust your AF in-camera with a focus chart.