Pentax K10D back focus issue

[santino]

Hello to all!
I have got myself a K10D for a Pizza pie and a beer. I‘m really impressed by the natural image rendition of the ccd sensor. But there seems to be a problem:
The image is absolutely pin sharp in the View finder, but the resulting photo is blurred (back focus). Not only that, but the ‘in-focus’ beep and dot are on when the image appears to be in focus. Since I don‘t have AF lenses I use my SMC Pentax 55 1.8. Whenever I ignore the in focus image and front focus a bit it gets better.

Any ideas on how to fix it?

 

[rjbuzzclick]

I have a K110D, which is the lower-end camera of the same series as yours that I bought new in 2006 for many pizza pies and beer. I used several K-mount manual focus lenses without issue.

One thought would be to check to make sure that you have the eyepiece diopter adjusted properly for your vision (small black slide on top of the viewfinder eye cup), though I'm not sure this would cause your issue.

Another possibility is that there's something off in your focus screen placement. I replaced my focus screen with a Katz-Eye one that has a split-image and micro-prism ring in it which great help with manual focus. Unfortunately, they are no longer selling screens but their site is still up. Here's a link that shows how to remove the focus screen:
http://www.katzeyeoptics.com/files/install5.pdf

When I did mine, I don't remember any shims under the screen, but if you feel like digging into it, maybe your screen has been jarred from a hard knock at some point in its life.

The only other thought is that if your lens is a screw mount with a K-mount adapter and you have a non-Pentax adapter, I have heard of issues with those but I don't think that would cause discrepancies between the focus screen and sensor focusing.

Good luck!

 

[Swift1]

The K10D is a a great camera, but it is unfortunately known for focusing accuracy issues, and it doesn't have easily accessible focus calibration.
That being said, it does have focus calibration in a hidden debug mode.

Here are instructions to activate debug mode
https://oligofren.wordpress.com/2010/03/06/enable-debug-mode-without-external-program-on-k10dgx-10/


I found this while searching and have no affiliation with the website, but I did try it with my K10D and it does work. I will warn you to be careful and only enable the debug mode. The SD Card trick will (I think) give many systems that you can enable or disable, DO NOT do anything other than enable the debug mode.

Once enabled, somewhere in the main camera menu, you should now have an option for focus calibration. In the focus calibration menu, you will have 4 different AF point options, labeled (0, 1, 2, 3 I think), IIRC, the first option 0 is for the center point, after that I don't know how the other corelate to the other AF points so be careful what you do.

 

[charjohncarter]

I had a Pentax K10d and used it while doing local theater promo photography. It was flawless for me, but I have to say I never pushed it. I didn't know about the focus problems but I did many garbage light images with it and it worked fine. I hope the OP can fix his problem: my grandson now has that camera for much less the a pizza and a beer and it is still working.

Here is one with the K10d and a little fill flash (very little):

Eugene O'Neil Promos by John Carter, on Flickr

 

[Pál_K]

My K10D has a front-focus issue. I discovered it while photographing flowers and blossoms. I knew about the hack, but my firmware is 1.0 and I don’t think the hack will work with that version.

Regardless, I experimented with the camera and a 35/2.4 DA AF lens wide open and near its closest focusing distance. It was only a few millimeters off, so I’m living with it. For close photography I’ll rely on a smaller aperture to increase DOF and mask the problem. For non-close photos, usually the DOF is sufficient to mask the problem.

The K10D is my favorite digital camera, beating out my X-Pro1 and D700. It cost me only $10 from a friend, but the lens from KEH was quite a bit more.

 

[santino]

Thanks for all your suggestions!
The lens is a genuine K mount, so no adapter.
I put out my focus screen, it seems to be correctly in place (although I don‘t know about possible shims). Would I have to add shims to correct back focus?
Adjusting the AF sounds good.

One note: I‘m not a pixel peeper but the results are almost useless. Eg when I focus on the eyes the shoulder is in focus etc. The more I stop down the lens the more it back focuses.

 

[rjbuzzclick]

It's odd that focus gets worse when you stop down. It should get better with the increased DOF. Shake the lens to see if there's a loose element or anything not tightened down.

Might be worth trying another lens if you can.

Check that the position of the mirror is correct, that could contribute to focus errors.

You would need to add shims under the screen to bring it forward and correct the back focus of the lens. There might not be room for that under the frame that holds the focus screen, and if the lens is the issue, changing the position of the screen would mess up focus with other lenses.

 

[santino]

Update: I managed to try out an af lens and the results are the same.
I decided to use the original shim as template and am going to make my own, thicker shim. Am I correct that the af sensors „measure“ off the focus screen?

 

[Swift1]

Update: I managed to try out an af lens and the results are the same.
I decided to use the original shim as template and am going to make my own, thicker shim. Am I correct that the af sensors „measure“ off the focus screen?

I'm pretty sure that the AF system isn't related to the focus screen.
The AF sensors sit behind the mirror which is semi transparent. Some of the light from the lens is directed through the lens on to the AF sensor.

https://www.shutterbug.com/content/how-autofocus-works-story-behind-invaluable-tech-once-considered-%E2%80%9Cgimmick%E2%80%9D

 

[santino]

Thanks Colton!
That means I‘ve got to make my own shim and adjust the af in debug mode.
The camera was inexpensive but is well worth the effort! It’s already my favorite digital camera. Handling and IQ are just right. I‘ll post pictures soon.

 

[Pál_K]

Do you have version 1.1 of the firmware? I don’t think the hack works with 1.0 and I vaguely remember others saying the hack no longer worked for them.

 

[santino]

I have not figured out yet how to check the firmware version.

 

[Swift1]

I have not figured out yet how to check the firmware version.

Turn the camera on while holding the menu button.

 

[santino]

Version 1.31
Luckily I found a site that explains how to adjust af in debug mode with a txt file and two sd cards.

 

[santino]

Ok.. I know I'm not very fast but here is a little test.

All shots were taken on a tripod. Focus point was the honey jar.
Lens was the genuine K-mount manual focus SMC Pentax 1:1.8/55

First shot was focused with measuring tape - tack sharp

Second shot was focused with my eye - back focus shift.

Third shot focused via af aid - back focus shift