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07-20-2016, 11:33 PM   #1
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An Open Letter to Pentax: K-1 Infinity Focus Problems

As a recent convert from Sony to Pentax, I have been anticipating the K-1 with so many features intended to astrophotography and night landscapes. However, I have been spending my first two weeks fighting an INFINITY FOCUS PROBLEM. Apparently, from forum and user group messages, this problem is not uncommon and has been noted by other pentax users.

PROBLEM: many K-1 bodies using many popular lenses cannot achieve proper infinity focus. The problem may not be apparent in everyday photography, but when pointed to star fields, the inability to achieve critical focus is obvious and apparent.

TESTING: While not a statistically valid sample, and not a rigorous test procedure, I have tried three different (new) K-1 bodies and several different lenses. Two of the three bodies could not achieve critical focus at all. The third was better, and perhaps even OK. Several different lenses were used to make sure that it was not a single defective lens. These included a 14mm Rokinon, a 35mm Pentax DA, a 50mm Pentax manual focus, a highly regarded135mm F2.4 SMC Pentax, etc. In general, of course, the longer the focal length, the more obvious the problem.

In most cases, I also took companion images with a Sony A7S, using similar exposures and lenses, to make sure that it was not a sky conditions problem. Both sensors are similar in size, although the K-1 has three times the resolution. Some of these images are shown below.

CONJECTURE: although I am a mechanical engeer mostly involved in software nowadays, i have no direct knowledge of Pentax designs or functionality. But, I have heard that some users can resolve the problem on some lenses by move the infinity focus stop on the lens - this works with Rokinon manual lenses, etc. So, this would seem to point to a misalignment of the sensor board within the camera body; possibly a manufacturing tolerances problem rather than design, pe se.

CALL TO ACTION: Pentax needs to do something! This is an astrophotography oriented camera that can't focus properly. I am sending a copy of this letter to Pentax USA. If you are having a similar problem, then you should too.

As for me, I give up. I have invested more than $2500 and two frustrating weeks trying to pin this down. I am going to return the body to poor Samys Camera, if they will let me do so, try to resell or return the lenses, and go back to SONY ...

IMAGES:

It is difficult to "match" images when the sensor resolutions are so different. I gave up trying. You only need to spend a little time looking at the Pentax monitor in LIVE VIEW to know something is wrong.

Pentax (Body 3, 7/20/16):

{it is a pain to show image on Pentax Forum, so please refer to:

Open Letter to Pentax - K-1 Infinity Focus Problems: Pentax SLR Talk Forum: Digital Photography Review

07-21-2016, 12:05 AM   #2
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Focusing on the stars in the night sky is undoubtedly tough and requires lots of patience, no matter what equipment you're using. In your second set of shots, both seem out of focus, albeit only slightly.

This really sounds like a lens problem more than a camera issue; minimally more evidence/testing would be needed to confirm things either way.

With regard to the problem you're describing, as you turn the focus ring, are you able to go past critical focus on both the left and right sides? Also, when shooting, did you have SR disabled?

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07-21-2016, 12:30 AM   #3
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Out of my curiosity, Can your K-1 achieves proper infinity focus while taking photo during it is enough light such as taking photo out door during day time?
07-21-2016, 01:11 AM - 1 Like   #4
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you should read this Who Killed Infinity Focus? | explora

07-21-2016, 01:33 AM - 1 Like   #5
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QuoteOriginally posted by rcolman Quote
As a recent convert from Sony to Pentax, I have been anticipating the K-1 with so many features intended to astrophotography and night landscapes. However, I have been spending my first two weeks fighting an INFINITY FOCUS PROBLEM. Apparently, from forum and user group messages, this problem is not uncommon and has been noted by other pentax users.

Dear friend, it's not a problem of camera. Almost all manual (and AF too, by the way ) focus lenses (especially, old lenses) has no 100% accuracy with infinity. It's well-known fact for many users, but not for you. The tolerances were lower for film cameras.
Some of manual focus lenses fans give lenses to the master who could overhaul lens to make infinity with digital cameras.

.

---------- Post added 07-21-2016 at 01:42 AM ----------

QuoteOriginally posted by i83N Quote
direct hit

Last edited by Parallax; 07-21-2016 at 07:52 AM. Reason: Rude comment removed
07-21-2016, 02:01 AM   #6
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QuoteOriginally posted by ogl Quote
Dear friend, it's not a problem of camera. Almost all manual (and AF too, by the way ) focus lenses (especially, old lenses) has no 100% accuracy with infinity. It's well-known fact for many users, but not for you. The tolerances were higher for film cameras.
Some of manual focus lenses fans give lenses to the master who could overhaul lens to make infinity with digital cameras.



---------- Post added 07-21-2016 at 01:42 AM ----------



direct hit
Sorry to hear that and I don't have a K1, but I have similar experience with my K5/K3 with original tele-zoom lenses, such as the 50-300 HD and non HD, the focus shift is quite noticeable with naked eye, I always have to override the focus a bit at the long end to maintain sharp focus, I only got one copy of the same lens I can't tell what to blame, since I am used to MF as I am from the 'film era' this is not a big problem to me, just hope Pentax will improve things in time..

Last edited by Parallax; 07-21-2016 at 07:52 AM.
07-21-2016, 02:38 AM   #7
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So... what exactly is the problem?
Please provide precise replication steps.
07-21-2016, 02:44 AM   #8
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QuoteOriginally posted by rcolman Quote
the longer the focal length, the more obvious the problem
So the longest focal length (and quite likely the second longest) are possibly M42. I have to ask the obvious - are you using an infinity capable adapter?. And why do you feel the need to have 3 posts here and one on DP all on the same issue?

07-21-2016, 03:44 AM - 1 Like   #9
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First, any astro-photographer with a little experience will never use AF for astro images, so, I don't think that the author of this post is using AF.

Second. in my astro-photo trials with Pentax cameras, I have meet with this problem in some of the cameras. More, on a K-5IIs, the bayonet on the camera was not only too far in the front, making focusing on the star impossible, but also was tilted. Not much, to be seen on a day time picture, but enough to give different images of stars on one side from the other. And the tests I have made was done with 2 lenses, which was working perfect at stars with my previous K-5. It took me some hours of screwing and unscrewing - in very small increments - the screws that holds the bayonet mount, to fix the problem. But I can do it, thanks to the seal ring, which stand under the the mount ring.

Third. Yes, some lenses are a little longer in the back, and cannot focus properly at infinity. I have met this case to, with a Tamron 70-300 mm. It was fixed on the service.

My conclusion is that this problem can appear, but can be fixed.
07-21-2016, 03:55 AM - 1 Like   #10
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Are you aware that it is pretty easy to adjust and calibrate infinity focus on M42, K,M,A lenses? AF lenses usually have some slack in the mechanism on the infinity end of the focus travel, combined with an inherently loose manual focus rings on AF lenses can make precise focusing difficult.

Using Manual focus with magnified Live view Is standard technique for Astro landscape photography.
07-21-2016, 04:58 AM   #11
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I really don't believe that autofocusing with any camera brand is going to get you too far. The shorter the focal length, or the wider the lens, there is just too little light available in order to make any determination.

If you are bound and determined to use AF, I would suggest, while there is still light - or earlier in the day, focus on something a mile or so away. Then put the body in manual focus along with the lens switch (if any), then using Gaffers tape - tape down the focus ring and you are all set for a night's shooting. This works very well with Milky Way shooting, or wide field. It may work OK on deep sky objects - Andromeda Galaxy with a 200mm+ lens, but I have never tried that type of astrophotography before, so YMMV. This should save you at least a half an hour of futzing around in the dark trying to get decent focus. Note, you should be able to AF on the Moon. If the Moon is out, it's usually not prime time for astro.....

Here are some other suggestions....

Last edited by interested_observer; 07-21-2016 at 05:08 AM.
07-21-2016, 04:59 AM - 1 Like   #12
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These forums could probably host hundreds of 'ópen letters' to Ricoh a week if everyone who had a camera or lens problem decided their issue required such bombast.
07-21-2016, 05:17 AM - 1 Like   #13
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just think how hilarious it could be to read them @rawr
07-21-2016, 05:22 AM   #14
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This is likely obvious but thought I would check as I have made this mistake before and it can make objects appear slightly out of focus. Was shake reduction turned on? If so definitely keep it off.
07-21-2016, 05:23 AM   #15
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QuoteOriginally posted by Digitalis Quote
just think how hilarious it could be to read them
Indeed. I expect a lot of the 'open letters' would be about the strange knocking sound people hear in their new Pentax.
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