[bwDraco]

My Pentax K-3 II has been suffering from occasional focusing problems where the camera may lock focus far off target at times even in good light on a high-contrast subject. The error is typically front-focus but can sometimes be back-focus, and cannot be addressed by AF fine adjustment because of its inconsistent nature. The behavior also appears to be somewhat dependent on color temperature. All of my lenses are affected.

I tried cleaning the AF sensor with a blower bulb and while it appears to have improved, it did not completely address the problem. Should I try again, or send in the camera?

Has anyone else sent in their cameras to Precision for this issue, and did they address it effectively? If I'm to send mine in, should I send in the lenses as well? The camera is out of warranty, but that's not an issue for me.

Draco

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It turns out the problem is delamination of the AF sub-mirror. How this is even possible is beyond me, but it looks like this will have to be sent to Precision.




Anyone else experienced this issue? Here's the note I'd send with the camera:

Phase-detection autofocus is inconsistent and sometimes produces very inaccurate results. Closer inspection of the mirror assembly indicates delamination of the AF sub-mirror.

Draco

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Last edited by bwDraco; 05-20-2018 at 09:17 PM.

[stevebrot]

It turns out the problem is delamination of the AF sub-mirror. How this is even possible is beyond me, but it looks like this will have to be sent to Precision.

Anyone else experienced this issue? Here's the note I'd send with the camera:
QuoteQuote:
Phase-detection autofocus is inconsistent and sometimes produces very inaccurate results. Closer inspection of the mirror assembly indicates delamination of the AF sub-mirror.
Images will be posted shortly.

Well, that would be consistent with the symptoms, though it is hard to say what might have been the cause.


Steve

[bwDraco]

I took a closer look at my old K-5 and I found similar delamination of the AF sub-mirror. This points to a design flaw that Ricoh may not be aware of and needs further investigation.

Everyone, try gently lifting up the reflex mirror on your camera(s) slightly and examine the small mirror beneath it for delamination. Be careful not to touch the surface of the mirror; touch only the lower edge and consider using gloves. We need to find out if there's a hitherto unnoticed design flaw in the mirror assembly and if so, tell Ricoh about it.

I just sent a Tweet to Ricoh Imaging US regarding AF sub-mirror delamination; hopefully, this will get more attention about this problem.

Draco

[leekil]

Everyone, try gently lifting up the reflex mirror on your camera(s) slightly and examine the small mirror beneath it for delamination. Be careful not to touch the surface of the mirror; touch only the lower edge and consider using gloves.

Is lifting up the mirror in this way a good idea?

[bwDraco]

Found this thread reporting the same issue: autofocus inaccuracy, green spots on the mirror? - PentaxForums.com

If anyone else has autofocus sub-mirror delamination, please tell us about it. We might have a serious design flaw on our hands.

Draco

---------- Post added 05-21-18 at 02:07 AM ----------

Another thread reporting this problem: pentax mirror spots - PentaxForums.com

[Not a Number]

Seems more of a materials failure or manufacturing error than a design flaw to me. I'm willing to bet that the design of the mirrors hasn't changed significantly from K10D on.

[Dericali]

Found this thread reporting the same issue: autofocus inaccuracy, green spots on the mirror? - PentaxForums.com

If anyone else has autofocus sub-mirror delamination, please tell us about it. We might have a serious design flaw on our hands.

In this thread the poster makes out that they cleaned the spots, so are you sure it's delamination?

[bwDraco]

On my camera, some of the spots bleed into the edge, so I'm pretty sure it's delamination.

I suspect the OP of that post merely pushed out the bubbles during "cleaning".



Draco

[stevebrot]

Found this thread reporting the same issue: autofocus inaccuracy, green spots on the mirror? - PentaxForums.com

Another thread reporting this problem: pentax mirror spots - PentaxForums.com

Both of those threads involved contaminants on the mirror surface and AF on both improved with cleaning, something I would not do unless willing to waste the mirror.

Do you have photos showing the delamination and its extent? The sky is not falling unless one has a few pieces of it to pass around.


Steve

[bwDraco]

Both of those threads involved contaminants on the mirror surface and AF on both improved with cleaning, something I would not do unless willing to waste the mirror.

Do you have photos showing the delamination and its extent? The sky is not falling unless one has a few pieces of it to pass around.


Steve

I think I did post photos. Are you able to access Imgur?

Draco

[link81]

i'll check my 3II, 30, and *ist when i get home

[jpzk]

About the "sub" mirror area to check ... does it mean to look at the bottom of the mirror when looking at it from the front ??
Apologies in asking ... I can't find the "sub" mirror. (dumb?).

[stevebrot]

I think I did post photos. Are you able to access Imgur?

Draco

Sorry, I did not see your edit to the original post. Those look like the spots from the other posts and possible evidence of liquid infiltration at the edges. When you said delamination, I expected something like the material lifting from its substrate.

Good luck with Ricoh or with giving this delamination idea "wings".

By any chance have you or a previous owner ever wet-cleaned the sensor or main mirror?


Steve

[stevebrot]

About the "sub" mirror area to check ... does it mean to look at the bottom of the mirror when looking at it from the front ??
Apologies in asking ... I can't find the "sub" mirror. (dumb?).

The main mirror is half-silvered and acts as a beam splitter with a portion of the light being reflected down to the PDAF sensor at the bottom of the mirror box by way of an auxiliary mirror angled down from the back of the main. This second mirror folds up and stows against the main mirror back with the mirror is in the "up" position, so we normally can't see it. The OP and others have been able to peek at this mirror by manually lifting the front edge of the main mirror a little.


Steve

[unapye]

This problem also occurs in Pentax k-1.

However I do not want to lift the mirror because I'm afraid that I will damage something but the symptoms are the same.
AF inconsistance is most visible with the DFA * 70-200 lens. The problem appears on distances of somewhere 10 meters and more. At first photo - front focus by half the distance, the next shot - back focus by 20 meters, next one - front focus by 1 meter, and another one almost accurate and so on. One photo of ten is spot on. I have checked two copies of DFA * 70-200 on my camera and both my lens and my friends one are completely unpredictable on my Pentax k-1. While the same friend's lens with his k-3 and other cameraz is always perfectly accurate.

I know that my cockeyed k-1 is not the only one.
This guy has exactly the same problem with his Pentax k-1 and DFA* 70-200.
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