Debug mode on K20D - works nicely


Link Posted 06/01/2010 - 12:38
I don't like test charts either, they have always given me misleading results.

I setup using a near infinity subject like a car number plate and working in 5 unit steps from -10 to +10, I review the results and work around the best in 1 unit steps. I always recheck the AF from both directions to ascertain there is minimal backlash.

If doing it for a zoom lens I check at the wide, mid and long ends.

I then repeat the above for a mid distance and then a near distance (approx 2m).

I generally find that the results are pretty close and adopt a nominal best setting. Critical focus is fairly easy to see as the text usually becomes very dense and sharp. When OOF, the text tends to loose contrast and small halos appear around the edges. I usually review my results on the rear screen at x11 setting (which is approx 1:1 on a K20D)

When I check my setting at macro distances, i.e. the closest focus point, using a test chart, I usually find that there is more DOF behind the focus point than in front (but the focus point is sharp). If I set for equal balance, I find critical focus on most objects at further distances become more OOF as you approach distance/infinity objects.

I've heard it stated by ex-Pentax engineers, that Pentax lenses are designed to perform in this manner as well as many others.

Anyway, it works for me! I find that most of my lenses require quite minimal adjustments, but it does make a difference.

As a footnote, I would never buy a camera now that didn't have individual AF micro adjustments.
Best regards
Richard Day

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Last Edited by RichardDay on 06/01/2010 - 12:39


Link Posted 07/01/2010 - 11:16
andymcm wrote:

Unfortunately when I went to confirm this behaviour this morning, I found that the focus on my FA 50mm 1.4 was wrong again. So I reset everything back to defaults, in the debug menu and the standard menu, and now it's focussing correctly at the defaults. This doesn't make any sense to me. I'll need to do a bunch more tests to work out what's going on.

Well after some more tests it seems that I get quite different AF behaviour depending on the lighting. In daylight my FA 50mm 1.4 needs to be at factory defaults. For tungsten lighting it needs to be at -10. I couldn't quite believe it was lighting, so I tried varying all other parameters I could think of, e.g. turning off and on shake reduction, but the only thing that affects it is the lighting.

A google search threw up this comment on another forum:

"Don't shoot test targets under Tungsten light if you want to fine-tune AF for daylight shooting. Tungsten light will cause the AF system to slightly front focus. This holds for every Pentax DSLR before the K-7."

I'm somewhat relieved that this seems to be a known issue, i.e. it's not a problem specific to my camera, but I'm frustrated that I'm now going to have to tweak my focus adjustments depending on the light. How tedious.


Link Posted 07/01/2010 - 11:22
You don't have to do that, just use the Quick Shift to make a final tweak to the focus point.

I can't help but think that it would be madness to recalibrate the AF every time you went from daylight to tungsten. Whatever would happen if you were in a situation where you were using both types of light?

The provision of adjustment isn't intended to be used in this way.
Best regards, John


Link Posted 07/01/2010 - 11:35
FA 50mm and many other lenses don't have QS.


Link Posted 07/01/2010 - 12:01
True. Manual focus in those circumstances I think. AF is not suitable in all circumstances.
Best regards, John


Link Posted 07/01/2010 - 12:42
I calibrate mine in natural light, at a focus distance of about 2-3 metres, as thats the distance I am from a model in a studio, where you do need critical sharpness on the eyes.
It doesn't bother me if the focus is slightly out at longer distances as I am unlikely to be shooting wide open.


Link Posted 27/12/2021 - 17:57
andymcm wrote:
iceblinker wrote:
Is there a debug mode for the K-7?

Yes there is. The basic procedure for all models is here:

There's enough info there to try it out, but I'll look at putting together some (K20D-specific) AF-adjustment instructions over the next day or two.

Just used this post to adjust the back fousing issue on a K-m I had given to me. Very handy information

Pentax K1ii, K3, K-m & MX-1.
Pentax LX, MX, ME Super & MV.
"Old Skool" with the new!
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