Focus Oscillation in K3 iii?

Started Aug 11, 2022 | Discussions thread
OP JoeOptics314 Regular Member • Posts: 143
Re: Focus Oscillation in K3 iii?

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.  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.

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David Lees

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