[Abram]

Hi guys,

I need some help here in trying to understand the AF system on the K-1. I am using all the FA Limited primes and the DFA 100mm Macro, I haven't been able to get accurate results using autofocus at any aperture on any lens. I have tried fine tuning each lens, but sometimes the lenses back focus and sometimes they front focus. I am simple and not demanding with my autofocus needs. I only use spot AF which is just the center point. I don't use continuous AF and don't need it. I just want things to be in focus lol. (Granted it's subtly out of focus but enough to be able to clearly tell).

Primarily I am a film shooter with manual cameras and lenses so I have basically only been able to use the camera as a manual focus body because at least I know what I want to have in sharp focus will be there.

What can I try to improve the consistency and accuracy? I want to love this camera but I'm running out of ideas and getting frustrated.

[photolady95]

Perhaps a photo or two posted with EXIF intact and others can help you figure out what's wrong or what you're not doing right.

[micromacro]

Pictures would help of course. And your settings as well.
Like I noticed that setting AFC and shooting still, or very little moving subject is not so forgiving with K-1 than with K5iis. Again, it's my experience, and I'm not an expert. The release button is somehow different also.
It's strange that you can't get precise focus with any lens at any aperture. Maybe something wrong with the camera.

[pschlute]

I have tried fine tuning each lens, but sometimes the lenses back focus and sometimes they front focus.

Either the camera is faulty or your fine tuning technique is. You need to use a tripod, widest aperture, spot AF, and a focus chart in natural lighting if possible. You need to do at least 10 tests, manually changing the focus back to either infinity or closest focus before repeating. Do not expect the AF to find the same spot each time, but you should find where the majority either back or front focus and adjust from that point. Review each shot at 100% on the lcd screen.

If the camera really does jump from front to back focus then send the camera back

ps. I am assuming you meant in your original post that the front/back front focus jumping was occuring with a single lens ?

pps Are you sure you are adjusting focus for individual lenses and not globally ?

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Last edited by pschlute; 03-12-2017 at 08:01 PM.

[kiwi_jono]

As others have said it would be useful to know what settings you are using (AF mode, number of points etc).

Couple of questions thought:
* Did you use focus charts with tripod for fine tuning? Otherwise its all guess work in my experience.
* Have you tried focusing in LV - this should be accurate regardless of AF adjustments.

[stevebrot]

I have tried fine tuning each lens, but sometimes the lenses back focus and sometimes they front focus.

As noted above, example photos are helpful.* A few questions:

• What are your expectations? What constitutes missed focus with your usual choice of subject?
• How are you assessing the need to do AF fine adjustment?
• Similarly, how do you confirm successful AF adjustment?

Do those questions sound silly? They sort of are, so I will clarify a little. Your signature includes two very fine quality rangefinder cameras, both of which are capable of extremely precise focus, though not with all subjects. Nailing focus on the front of a grapefruit at 1.5m may be difficult, for example. The sides are easy, but the front, not so much. Your K-1 has similar limitations relating to curved surfaces, receding surfaces, and the size of the AF point. As with your MP, your K-1 should be able to nail focus on a high contrast flat target at moderate distance, assuming proper calibration.

Whether the K-1 is as consistent in doing so as your MP, is another question. It is not unusual for PDAF (all brands) to indicate a focus variance of as much as a millimeter +/- of best effort using magnified live view when focusing with fast lenses at moderate distance. The ability to detect an out-of-focus state is the same with an f/1.4 lens as with an f/2.8 lens and with an f/2.8 lens is limited by DOF in much the same way as when focusing directly using an optical viewfinder. That being the case, for any number of focus attempts with an accurately calibrated system, a fair number will be back-focused and a similar number will be front-focused. For all but the most demanding tasks and at normal viewing distances/magnification, this precision is perfectly adequate at taking apertures f/2.8 and narrower.

I have reviewed your Web page and am impressed with your work. I can confidently state that you should be able to get similar results from your K-1 using the lenses you mentioned in your post. With any luck your examples will hold some clues as to what is awry.


Steve

* Unedited in-camera JPEG, linked from another site or cloud storage. Uploading to Pentax Forums strips the EXIF.

[2351HD]

I experienced the same issue with my K1 and 15-30mm lens. The thing could never AF to the right spot, no matter AF fine tune or not.

I am a 645z user and it has never missed a beat.

I returned the K1 and 15-35, purchased a Canon 5DmkIV and never looked back. Just wish the 5D4 had the screen from the K1.

[stevebrot]

I don't use continuous AF and don't need it.

This is just a shot in the dark, but when using AF-S, are you set for focus priority (Rec Menu 1/Phase Detection AF/AF-S Setting)? If set for "release priority" the shutter will release even when focus has not been attained. Release priority is usable, but care must be taken that focus has actually been attained (green hexagon) before releasing the shutter.

There is also the outside chance of dust on the AF sensor. This can cause poor precision and failure to attain focus.


Steve

[lennyl]

my first K-1 had inconsistent and inaccurate AF (tested with central AF point ofcourse). I made 3.000 shots and no settings did not help.
various lenses: APS-C DA, APS-C DA*, FF FA Limiteds, new D-FA 24-70/2,8...

I sent back K-1 (SRS Microsystems UK) and the new body is OK.

[Abram]

Hi everyone,

First off thank you all for taking the time to respond, please know I'm not just trying to be a complainer!

To help clarify my concerns:

• When I stated that the lenses will exhibit front AND back focus, I was referring to each lens in that sometimes each one will behave differently.
• In stating that I applied fine-tune adjustment to the autofocus it was done on a per-lens basis and not a global adjustment.
• When doing the fine-tune adjustment I did use a tripod and a proper focusing chart and checked the results carefully while tethered to my computer via Lightroom.
• The AF settings I've been using have been AFs with the single selectable point or Spot focus, I haven't even tried AFc yet.

As a little aside, I do have extensive experience with most camera brands, I came from the Canon world originally and shot with the EOS system for 10+ years. I switched over to Leica around 2013 and though I'm not using their digital cameras anymore I am using their film bodies along with other manual focus film systems (Nikon F, Hasselblad 500CM) so I am very comfortable with manual focus and it often suits my workflow. I also haven't used a traditional DSLR since selling my 5DmkIII in 2013 so my only autofocus usage since then has been mirrorless systems with CDAF. It's entirely possible that I have just forgotten about the potential inaccuracies of a PDAF system. I fully appreciate that many AF systems can struggle with wide open apertures, but to be honest I really only use large apertures when try to specifically isolate a subject. Most of the time I'm somewhere in the f/4-f/8 range, which is where my frustration comes in. When I can tell that the point of sharp focus is not where I intended at f/5.6 (rather having it slightly behind or in front of the subject) at moderate distances I am just baffled by that. I don't seem to have any trouble when I'm locked down on a tripod, but as soon as the camera is OFF a tripod it's wildly different. And though I do drink a lot of coffee, I'm not so jittery as to not be able to hold steady to take a shot. Case in point. I can still get sharp images from my Leicas in the dark at 1/8-1/15 sec exposure times.

Even in adjusting my lenses, my FA77mm originally required a -10 adjustment when on a tripod and then as soon as I was shooting in real world scenarios nothing was in focus so I had to reset it to 0 which worked for a little while and now it's somewhere around a +3-4 adjustment.

I will try to pull up some images that demonstrate my concerns, and I definitely want to figure this out, so again thank you all for being willing to help!

[pschlute]

Abram

Thanks for the clarification. The camera needs to go back to be replaced or repaired.

[Abram]

Ok here are some quick samples. Nothing fancy mostly just snapshots but hopefully they exemplify what I'm talking about. I do often "focus & recompose" but the ones that are clearly out of focus should have EASILY been in focus in my opinion.

Dropbox - K1 Samples

Also I did confirm that my camera was set to Focus Priority and not Release Priority (but thank you for having me check that!). I'm guessing it's also a limitation of these older screw-drive lenses, I'd bet that these same copies would have been completely fine and accurate on film. (I had a similar issue with the Leica Monochrom vs my film MP where the same lens looked perfectly sharp on film but clearly off on the Monochrom.)

On that same note, would I perhaps be better served by something like the DFA 24-70mm? I kind of loathe the idea of having to use such a large zoom, but I am willing to if that's what it'll take to have usable / reliable autofocus for this thing. Also to note, I am not shooting commercially anymore and the vast majority of my personal work is done on film. By profession I am a designer so I'm primarily using my digital setup for the times I need imagery for my design work or for documentary purposes. My bias / preference is heavily towards small and compact setups (thus, Leica) so the FA Limited primes are what really swayed me to the Pentax in the first place.

I'm not opposed to sticking to manual focus, as the majority of my work allows for it, but I just would like to know that when I need autofocus it will be IN focus

[GodsPetMonkey]

Ok here are some quick samples. Nothing fancy mostly just snapshots but hopefully they exemplify what I'm talking about. I do often "focus & recompose" but the ones that are clearly out of focus should have EASILY been in focus in my opinion.

PDAF has a tolerance, and in the case of the center point you are using that is f2.8. That means for a certain percentage of the time (probably 95%?) a suitable object covered by that PDAF sensor will be in the acceptable 'in focus' field at f2.8 or smaller. As this is a tolerance thing, sometimes it'll be right at the edge of that 'in focus' field, and thus, at 100% be just a bit softer than if it totally nailed it. This isn't a Pentax thing, this is how PDAF works and it is no different for Canon/Nikon/Sony. It is also worth noting the CDAF has a tolerance too (which can be really obvious if you have focus peaking on... which also has a tolerance!), though it tends to be tighter, but that does depend on the subject and lighting conditions - no AF is perfect.

Looking at your samples some of the photos may come under this - the focus point is just in the range, or the PDAF sensor covered more than just the foreground element and thus what you thought was the focusing point is a bit bigger (photos one and four). Most of the others, however, show really nasty back focus. Now it could be that they are just the AF outliers; the result of the occasional AF hiccup (meaning it falls into that 5% or whatever sized caveat the manufacturer allows), but your description has it happening way to often. Based on those photos something certainly looks amiss, and you should take the camera back for replacement/repair.

Even in adjusting my lenses, my FA77mm originally required a -10 adjustment when on a tripod and then as soon as I was shooting in real world scenarios nothing was in focus so I had to reset it to 0 which worked for a little while and now it's somewhere around a +3-4 adjustment.

That's certainly not normal. AF adjustments should be either different across certain lenses (ie. certain lenses require the adjustment to be made) or reasonable consistent across all lenses (ie. the PDAF sensor requires the adjustment), but above all, they should be stable - unless something took a major whack the adjustment should not need changing.

If the adjustment needing is changing that much (and that is way more than a tweak due to more accurate testing) it makes me think that maybe your PDAF sensor is loose. That's a warranty issue - time to take the body back.

[MarkJerling]

I'd strongly suggest that you set up a focussing test using a tripod and a focus test chart, easily obtainable from the internet. It's entirely possible, looking at your examples, that your camera is not focusing where you think it's focusing.

[Abram]

I'd strongly suggest that you set up a focussing test using a tripod and a focus test chart, easily obtainable from the internet. It's entirely possible, looking at your examples, that your camera is not focusing where you think it's focusing.

That's precisely how I did my focus test (which I mentioned in my post above). I'm totally willing to try it again but I was very careful / precise during the process and I've also done it before on other systems so I'm familiar with how to adjust focus.

---------- Post added 03-13-17 at 03:47 PM ----------

Based on those photos something certainly looks amiss, and you should take the camera back for replacement/repair.

That's certainly not normal. AF adjustments should be either different across certain lenses (ie. certain lenses require the adjustment to be made) or reasonable consistent across all lenses (ie. the PDAF sensor requires the adjustment), but above all, they should be stable - unless something took a major whack the adjustment should not need changing.

If the adjustment needing is changing that much (and that is way more than a tweak due to more accurate testing) it makes me think that maybe your PDAF sensor is loose. That's a warranty issue - time to take the body back.

Thank you for the clear and helpful response. Regarding warranty, I bought the K-1 body used (barely) so I'm not the original owner but I do have the original purchase receipt and it was originally purchased in August of 2016 before I purchased it in January of this year. It still falls within the initial year of warranty but will I be eligible?