john_mathius

Ok, I've been able to get ahold of another K10d, and it turns out that all of my problems

have now disappeared. No more focus issues with any lens, at any focal length. This

is interesting. I think I may send in this k10 and see what they say.

I'm going to compare the exif data to see if this other k10 is significantly different than

the old one.

Hello,

I'll chime in as well, and report a solution that seems to have corrected most of my

trouble.

I've a K10D body, and am just beginning my foray into pentax glass after having

swapped from another well known manufacturer. I noticed the focusing issues right

after I picked up my DA* 16-50mm, and at first just attributed it to the well known

back focusing issues noted for that lens. However, when I put on my Sigma 18-

50mm F2.8 EX (wow! sharp!!) I found that it was now showing almost exactly the

same range of backfocusing issues as the DA* 16-50mm.

What??? The sigma was fine before hand (and I've saved images to back that up),

but after having the DA* 16-50mm on the camera for all of a half hour, the sigma

started to exhibit the same problem. At this point I was sure it was something to do

with the body. Maybe the body reads the particular focal length of the lens and

adjusts its memory table to alter the length of the primary light path. The 16-50mm

might have had some additional information to convey which updated the memory

table in a negative manner for that focal length range. Hmm. What to do.

I took a round of test shots with a focusing test chart at 45 degrees both right side

up and upside down, as well as a linear plane of objects at varying scalar distances

(percentage wise), and confirmed the backfocusing is similar with both the 16-50mm

DA*, as well as the 18-50mm Sigma. I then tried the other glass I own, a 50mm FA

1.4, and a DA 16-45mm. In the case of the FA 1.4, focus was perfect (well the

argument could be made that perfect focus is 1/3 infront, 2/3 behind but for the sake

of this argument consider 1/2 in front, 1/2 behind to be perfect). The DA 16-45mm

showed the same backfocusing problems.

At anywhere from 16- ~28mm, all three wide zooms showed similar back focus

(thought the 16-50mm DA* was the worst) while at 50mm or equivalent they all

appeared to be focusing properly. The 50mm FA 1.4 was spot on at 50mm.

After browsing the net looking for a solution, I found the 1.1 firmware with the hidden

debug mode. I modified the header with the 1.3 header (as already I updated to 1.3

firmware) and uploaded to the camera.

After playing around with the focusing system, I found that if I adjusted for one lens,

(and in my case, this in practice adjusts for the focal length not just a specific lens,

ie: adjusting for the 16-50 solves the 18-50 etc.) would often put another out,

specifically that there seems to be only one universal setting for front / back focus.

This setting I think is different for different focal lengths, or at least should be, as all

the lenses I've tried show the same problem. It may be possible (and I'll have to do

some more research to understand the math involved with calculating the distance

to the sensor for focusing) that the sensor is calibrated properly for 50mm, but is out

at the wide end. I would imagine that the wider lenses would show even worse

backfocusing (tok 11-16mm anyone?) on the wide end.

Could this be a result of a faulty memory table describing focal length adjustments?

I don't really have the skinny on how this works, so don't take this too seriously.

Regardless, I continued testing and found something interesting. After adjusting

back to zero with my 50mm FA 1.4, turning the camera off, then swapping to the 16-

50mm DA*, I found that adding +80 to fix the back focus, turning off the camera,

and swapping back to the 50mm FA 1.4, the camera seems to have remembered

that the 50mm was good at zero (but that is not indicated in the menu... it still says

+80.

Let me repeat this more succinctly, the 50mm was now spot on at +80 as indicated

in the menu... whereas before it was spot on at zero. At this point I was confused

as to how this would occur, unless the memory table somehow retained info from

the last lens, for a particular focal length. Ok, that was good, I confirmed it with a

few shots, and then went to bed.

The next day I started to do some more test shots, but was discouraged to find that

the camera had reverted to the original settings, of adjusting for one, outadjusts

another.

I did some more reading on the net about manually adjusting via screws on the

sensor the distance from the mount. Not prepared to do that until I understood more

concretely the math, I decided to continue to catalogue my issues.

Long story short, the solution I found goes as follows (though retaining this in

memory seems to be somewhat difficult to achieve, there may be some kind of write

procedure required or it loses the info after a certain amount of power off time.

1.start with the least problematic backfocusing lens (or alternatively the most front

focusing of your collection (up to four can be done with this method) and arrange

them in order of increasing back focus. This for me meant: 50mm 1.4, 16-45mm,

18-50mm, 16-50mm.

2.with the most front focusing (in my case the 50mm was perfect at zero) go to the

capture setting above the focus setting, and on the first line set the value to 1.

3.Calibrate the lens via the back/front focusing adjustment.

4.verify focus. Turn off camera. Swap lens to next in series (16-45 in my case)

5.Go to the menu as in 2. and increase the value +1.

6.Repeat steps 2-5 for each lens up to a maximum of 4.

When you are done, exiting debug mode and swapping lenses should produce

correct focusing for each lens. Whether altering the value in the capture menu

'actually' does anything, I'm not 100% on, as this procedure seems to work without

changing this value. However, it has shown improvement on the amount of time the

camera remembers the settings. (I will do a more concrete analysis of these

parameters when I borrow my partners k10d)

Anyhow, I hope that helps some of you. If this is far too scattered, I can write

something a little easier to read.