Focus Oscillation in K3 iii?

Started Aug 11, 2022 | Discussions thread
JeremieB Senior Member • Posts: 2,067
Re: Focus Oscillation in K3 iii?

JoeOptics314 wrote:

JeremieB wrote:

JoeOptics314 wrote:

I just received a Pentax 70-210 mm zoom and am comparing it against two other lenses that cover that zoom range (150-450mm and 55-300mm PLM). My initial shots comparing against the 55-300 mm showed it better in terms of blur, which would be quite surprising. But when I started taking pairs of shots a few seconds apart and compared the pairs taken with identical manual settings I see what appears sharpness differences.

Here are some samples, displayed in ON1 Photoraw. These are unprocessed raws taken 2 to 5 seconds apart with identical, F/number, shutter speed, ISO.

I am wondering if there is some parameter in the K3 iii menus that might be causing this issue? I am shooting hand held, but with motion compensation on at what I think are reasonable shutter speeds (1/125 to 1/800 sec).

AF Mode = S

AF Active Area = S

AF Area Restriction = On

Release Priority (Hmmm. Should I be using Focus Priority?)

The fact that I see this focus change problem with 2 different lenses, must me the issue is the camera? Have others seen this problem? I am hoping there is a different setting that fixes the issue.

70-210mm at 210mm F/5

150-450 at 200mm F/6.3


- I wouldn't shoot handheld, or it's difficult to conclude anything. I would use a tripod

- I would use Focus priority and see if it's better

- in fact I would use live view and tripod for fine manual focusing

But I don't really know if you're testing the AF of your lens, or its sharpness ? If you test sharpness, then don't test AF at the same time

To me it looks like some of your shots are just out of focus.

Also at shutter speeds like 1/125 or lower, there could be some shutter shock maybe - you may try with electronic shutter then.

I was thinking the motion compensation being on would take care of the motion on the longer exposures.

It's not easy to see on your screenshots, but it doesn't look like motion blur.

The shake reduction system compensates up to some point. At long telephoto focal lengths, it's less efficient too.

But I am seeing the issue at speeds like 1/200 second. The images definitely look out of focus sometimes and that is exactly what I am puzzled over. Why sometimes it is sharp as a tack, perfect focus and sometimes it is not when doing repeated shots. I just had the problem occur on a tripod. I can not see it out of focus through the viewfinder. Only when I got back and view the recorded images on the camera.

On your screenshots it's zoomed a lot, so maybe it's normal that you don't see the blur through the viewfinder (maybe not).

That's weird. Phase detection can be imprecise but you seem to have good conditions to avoid that in your shots.

Maybe you could try excellent advice from MightyMike:

It saved my day at the time, maybe it's worth a try.

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