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04-09-2010, 02:27 PM   #1
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Pentax Imaging USA on K-x mirror shake issue

It has been 4 months since I am trying to resolve one way or another issue with my white K-x kit. It is that dreaded mirror shake issue on 1/60-1/125 sec.

It was sent to CRIS Camera (USA official repair facility) for repair where mirror box was replaced which did not help. This is test I did after it came back (has now close to 10 thousands hits):

http://i824.photobucket.com/albums/zz165/akpch/test/mirror_shake_k-x.jpg

(pls. don't embed it, it uses all my traffic)

Second time at CRIS they would not acknowledge problem and send it back. Contact via online chat and pentax asked me to send into via e-mail for review. Two weeks later there is no response so I am calling them on the phone. And here is official response:

We reviewed all the cases of camera shake, EXIF info and concluded it is user error each time. I am free to send camera for repair as many times as I want provided I pay shipping but since problem is not acknowledged no repair attempts will be made. Pentax would not replace or refund full or partial purchase price since the problem does not exist.

Anyone needs white K-x kit for parts?

04-09-2010, 04:24 PM   #2
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Well that response means it either really is user error or else it's endemic to a significant percentage of K-x production ...
04-09-2010, 04:47 PM   #3
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Have you tried the test with the same shutter speeds on a tripod, or...dare I say it...a tripod AND shutter release cable/timer?
04-09-2010, 05:07 PM   #4
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QuoteOriginally posted by akpch Quote
We reviewed all the cases of camera shake, EXIF info and concluded it is user error each time.
One part of the problem are the unsystematic tests made by both the users and Pentax themselves.

I suggest that a test along the lines of the following excellent test of P. Smith is made
-> Study of the Effectiveness of Shake Reduction in the Pentax K7

Ideally, copying his exact test procedure as it yields a comparison with a camera which has been shown to be free of the artifact, Smith's K-7.

This should yield a clear result. Showing images which are blurred at 1/100s is good evidence but as it turns out, not good enough.

My current feeling really is that some K-x are affected and a clear test procedure is missing for Pentax to verify.


I read that not all photos are affected. An quantitative examination of the affected percentage could help as well. In Smith's test, this shows up as variation of the blur width.


Note: P.Smith used a program which is limited to 50 image analysis for free (QuickMTF). For larger work, Peter Burns' free SFRedge (imagescienceassociates.com) can be used. Just quote 1/2 of inverse cy/px where MTF=50%.


Last edited by falconeye; 04-09-2010 at 05:16 PM.
04-09-2010, 06:02 PM   #5
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It seems like only white bodies affected, I started thread on another forum to collect more info about serial numbers and body colors.

Also the issue is very consistent with my K-x at least and easily reproducible:

contrast subject (text), 1/60 - 1/125 sec exposure, handheld. That is all I asked Pentax to test. In response they sent me back picture shot on tripod and copies of pages from manual where it says - one should always use tripod for macro photography - 1 meter (3 feet) distance they consider macro.

Then there is no issues shooting 1/30 sec. If I had such bad handholding technique, would not it be worse? I am proud to say that I was able to take perfectly sharp pictures with Canon, no SR, IS or any other kind of stabilizer at 1/10 sec, 28 mm lens.


What you see on my test are sequential shots takes one after another. It is 100% reproducible, visit my house and try yourself if you want to.


I guess I have to make youtube video about this issue.
04-09-2010, 06:29 PM   #6
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QuoteOriginally posted by akpch Quote
It is 100% reproducible, visit my house and try yourself if you want to.
I believe you. I justed wanted to help you to seal it in a way Pentax would have to accept it too...

You may try to PM some US forum members with known links into Pentax to help you out.

I.e., I know of one person here in Germany (and the dealer in charge) who got his K-7 replaced because of some SR problem too. He reports his new K-7 works w/o fault now. The case is currently under investigation by Pentax Germany.

And to be fair ... it may be difficult to reproduce for somebody else when handholding your camera. Please, ask a friend to repeat the same test to be on the safe side. BTW, it is technically correct that the SR algorithm must assume the distance be much larger than the focal length. So, a big cross on the other wall of the room is better than a printed page. So, plenty of chances for Pentax to escape the issue
04-09-2010, 07:12 PM   #7
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QuoteOriginally posted by falconeye Quote
I believe you. I justed wanted to help you to seal it in a way Pentax would have to accept it too...
..
Guess I am getting too defensive after all these problems. My apologies. Let see if anyone who has pentax connection in US appears.
04-09-2010, 07:14 PM   #8
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Interesting that you said this only applies to "white" k-x. Makes me want to give mine a closer examination.

it'll be interesting to see if the different colors of k-x go thru different types of assembly batch.

04-09-2010, 07:27 PM   #9
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QuoteOriginally posted by tokyoso Quote
Interesting that you said this only applies to "white" k-x. Makes me want to give mine a closer examination.

it'll be interesting to see if the different colors of k-x go thru different types of assembly batch.
'only' is just speculation. At least confirmed cases of mirror shake seems to be coming from white bodies.
04-10-2010, 05:37 AM   #10
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QuoteOriginally posted by akpch Quote
'only' is just speculation. At least confirmed cases of mirror shake seems to be coming from white bodies.
why does it only occur 1/60 - 1/125 sec? whats so special about that shutter speed range?

i did a few tries today. but i didn't see any visible difference thru the LV zoomed in whether with SR on or off. for peace of mind i'll turn off SR for now.
04-10-2010, 08:59 AM   #11
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not only white bodies!

I've got a blue body KX and get the double image at 1/60 sometimes, even when I've steadied my hands on a rest.

There goes the white body speculation.
04-10-2010, 09:08 AM   #12
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Interestingly if you search "Mirror Shake" on Google the first result you get is a result about the K-X issue.

You would think Pentax would be more concerned about the negative publicity. Especially when it appears as only a small subset of the total units.
04-10-2010, 09:29 AM   #13
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QuoteOriginally posted by tokyoso Quote
for peace of mind i'll turn off SR for now.
As P.Smith's study showed, SR on always yields better results than SR off (if the SR isn't defective), even for exposure times too short for the SR mechanism to be effective. It simply has no measurable effect then.
04-10-2010, 10:09 AM   #14
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heart rate?

The same test needs to be done with a tripod to eliminate any human factor.
Maybe it's your heart rate ...
04-10-2010, 10:17 AM   #15
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QuoteOriginally posted by stanjo Quote
The same test needs to be done with a tripod to eliminate any human factor.
Maybe it's your heart rate ...
Shake reduction test on a tripod?

One German photo magazine has constructed a camera shake device to be able to make reproducible SR tests. Maybe, Pentax should borrow their equipment?
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