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06-28-2008, 11:26 PM   #1
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AF problems with SDM lenses on K20D?

When making the first test shots with the newly received DA*200 on the K20D, I found the AF was having problems with this lens.

When focusing, the AF went either:

- close to the correct position and stayed a while there with the AF indicator blinking before going to the correct position and finally having the AF lock.

or

- when to subject was more distant than the actual focusing distance, it went a bit towards minimal focusing distance, stopped briefly moved again a bit in the same direction, stopped briefly until it reaches the minimal focusing distance.There it stands still, AF indicator blinking. Unless focusing manually, it would stay there whenever I press the shutter half way.

First I though it is the lens as I was not having any problems on normal lenses on the K20D.

Then I tried the lens on my K10D (firmware 1.30) and the AF was fast, reliable and precise. So I think it is unlikely the lens.

Finally I tried another SDM lens, the DA*50-135 on both K10D and K20D, and the K20D shows the same AF flaws as with the DA*200.

What surprises me, I used the DA*16-50 quite a lot on both cameras and this problem was somehow not as obvious as with the 50-135 and 200.

I think it is time to send the K20D in to Pentax for servicing.

How is your K20D performing with these 50-135 and 200 SDM lenses?

06-28-2008, 11:59 PM   #2
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Sound very strange and it looks as if it is a firmware bug, I'm afraid.


QuoteOriginally posted by tcom Quote
When making the first test shots with the newly received DA*200 on the K20D, I found the AF was having problems with this lens.

When focusing, the AF went either:

- close to the correct position and stayed a while there with the AF indicator blinking before going to the correct position and finally having the AF lock.

or

- when to subject was more distant than the actual focusing distance, it went a bit towards minimal focusing distance, stopped briefly moved again a bit in the same direction, stopped briefly until it reaches the minimal focusing distance.There it stands still, AF indicator blinking. Unless focusing manually, it would stay there whenever I press the shutter half way.

First I though it is the lens as I was not having any problems on normal lenses on the K20D.

Then I tried the lens on my K10D (firmware 1.30) and the AF was fast, reliable and precise. So I think it is unlikely the lens.

Finally I tried another SDM lens, the DA*50-135 on both K10D and K20D, and the K20D shows the same AF flaws as with the DA*200.

What surprises me, I used the DA*16-50 quite a lot on both cameras and this problem was somehow not as obvious as with the 50-135 and 200.

I think it is time to send the K20D in to Pentax for servicing.

How is your K20D performing with these 50-135 and 200 SDM lenses?
06-29-2008, 02:45 AM   #3
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Strange, no problems here with the 50-135 and my K20D.

As a note, though, I haven't upgraded my firmware. Is your K20D firmware upgraded?
06-29-2008, 09:21 AM   #4
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QuoteOriginally posted by cputeq Quote
Strange, no problems here with the 50-135 and my K20D.

As a note, though, I haven't upgraded my firmware. Is your K20D firmware upgraded?
Yes, mine is upgraded. I hope my usual shop has a K20D in the shop, so I will be able to check the DA*200 on that body before sending the K20D to Pentax.

06-29-2008, 07:34 PM   #5
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I've been using the DA50-135 on my K20 without any problems. The lens was horribly inaccurate with the K10, to the point I wondered if I had wasted my money on it. Since getting the K20, I've been MUCH happier.
06-29-2008, 08:49 PM   #6
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I've tried my DA*50135 on both K10D and K20D, both worked fine, but the results from K20D do seem abit sharper, but they are pretty sharp too from the K10D. Don't know if it's because the K20D's 15mp sensor or something else.

But it's a totally different story when mounted the DA*1650 on both cameras. I sold off my K10D in a week time after I got the K20D, mostly because of this lens ...
06-29-2008, 11:44 PM   #7
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Thank you mtngal and Frank. It seems I have a defective K20D then, I will send it in this evening and see what Pentax says.
06-30-2008, 12:08 AM   #8
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I haven't noticed any issues with any of my DA* lenses on my K20D, like the DA*16-50, DA*50-135 or DA*300.

06-30-2008, 07:25 AM   #9
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-- Moderator edit --

Unprovoked personal attacks like that are certainly not acceptable here!!

Last edited by joele; 06-30-2008 at 03:48 PM.
06-30-2008, 07:43 AM   #10
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QuoteOriginally posted by mtngal Quote
I've been using the DA50-135 on my K20 without any problems. The lens was horribly inaccurate with the K10, to the point I wondered if I had wasted my money on it. Since getting the K20, I've been MUCH happier.
Some early model K10D's are having problems with focus on the DA* lenses.

Needs to go in for an adjustment.

Dave
06-30-2008, 09:19 AM   #11
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Thank you for your replies

When AF is stuck on minimal focusing distance, it has nothing to do with adjusting. In cases where AF works correctly, the K20D focuses perfectly with both DA*50-135 and DA*200.
06-30-2008, 09:31 AM   #12
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QuoteOriginally posted by tcom Quote
- when to subject was more distant than the actual focusing distance, it went a bit towards minimal focusing distance, stopped briefly moved again a bit in the same direction, stopped briefly until it reaches the minimal focusing distance.There it stands still, AF indicator blinking.
Good description! It is revealing.

Because, as a matter of fact, one of the few advantages of phase AF vs. contrast AF is that the direction of correction can be derived from a single focus sensor measurement.

I.e., your lens moves in the wrong direction. It does so twice, then your firmware gives up with the blinking signal.

An easy way to achieve this is to revert-mount a focus sensor or its plug (if possible at all).

I propose to manually select any of the 9 cross sensors and study if they all show the same error.
06-30-2008, 11:44 AM   #13
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QuoteOriginally posted by falconeye Quote
Good description! It is revealing.

Because, as a matter of fact, one of the few advantages of phase AF vs. contrast AF is that the direction of correction can be derived from a single focus sensor measurement.

I.e., your lens moves in the wrong direction. It does so twice, then your firmware gives up with the blinking signal.

An easy way to achieve this is to revert-mount a focus sensor or its plug (if possible at all).

I propose to manually select any of the 9 cross sensors and study if they all show the same error.
The explanation makes sense, I tried out several sensors by selecting them manually, but came to the same result.

In the meantime, I explained the problem to Pentax Switzerland, they contacted Pentax Germany to discuss the following steps...

Last edited by tcom; 06-30-2008 at 01:10 PM.
06-30-2008, 12:12 PM   #14
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I have a followup to the problem...

I found it strange that the problem did not occur with my traditional focusing lenses. I tried several lenses, but could not reproduce the problem. The more the subject I wanted to capture was blurred, the more the error occured with the DA*200 and DA*50-135. I searched what lenses I could try which gives a great blurred bokeh. I choose to try it with the DFA100/2.8 macro lens, and I have exactly the same problem!

I point the lens to a flower around 1m away and focus on it. Then, I point the lens to a distant tree and press the shutter half way, the af turns the lens into the wrong direction, stops briefly, and continues in the same wrong direction before giving up.

falconeye, I think you are right!

Last edited by tcom; 06-30-2008 at 12:38 PM.
06-30-2008, 01:07 PM   #15
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QuoteOriginally posted by Sondek Quote
removed quoted deleted text - Joele
Wow... what happened here? I don't want to change this thread into a discussion of "netiquette", but I think most of us want to keep this forum free of personal attacks that does not have anything to do with threadstarters post.

Last edited by joele; 06-30-2008 at 03:46 PM.
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