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11-27-2022, 05:17 AM   #1
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16-50 SDM, AF problems, not consistent from infinity vs. closest setting

Hi,

Have just received my K3-3, so far satisfyed bet with a learning curve....
Trying to fine adjust my lenses, but have problems with my 16-50 SDM.
This particular lens have always had some minor sharpness issues, last year I did have hade it overhauled where also the SDM-motor was replaced. After that it was much better but still needed a -9 setting on my old K3-1.
Now when I try to fine adjust the lens on the K3-3 I recognize that when I set the focus at infinity and focus at my target the focus sit tack sharp but when focusing from closest setting the focus will be a significant front focus although not consistent.. HMMM..

Any ideas? to me it feels like a "play" in the mechanichs? or some optical issue?
Do you think converting to screw drive could be a solution??

/Claes-Ove

11-27-2022, 06:03 AM   #2
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If you have the means to self convert then you should try the conversion but I can’t see why it would work better unless the sdm is failing again.
11-27-2022, 06:49 AM   #3
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QuoteOriginally posted by Paridon Quote
Now when I try to fine adjust the lens on the K3-3 I recognize that when I set the focus at infinity and focus at my target the focus sit tack sharp but when focusing from closest setting the focus will be a significant front focus although not consistent.. HMMM
Welcome to the world of PDAF ! This is quite common, not specific to your lens or camera. This is why when doing a AF/FA adjustment I always advise you do 10 tests asking the AF work from infinity and 10 tests making the AF work from closest focus distance. Then use a setting that goes with the majority result.

I am afraid PDAF is just not as accurate or consistent as we would like it to be. Always been this way, but until we got larger MP sensors we never knew
11-27-2022, 08:02 AM   #4
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Thanks for your quick replays:-)

@UncleVanya; I have the intention to make it my self, (have already done it some times). But I really agree to your opinion. I can´t see why it should be better just an idea.

@pschlute; Yes, I imagine the "uncertainness" of the PDAF system, but in this case I have other lenses f.ex the DA17-70SDM which nails th focus more or less every time.
The discrepances with the 17-70 ar acceptable but with the 16-50 the abbrevations are "way out". Using a Datacolor Spyder LensCal the DA17-70 "nails" focus in fractions of 1 unit from "0", but with the DA16-50 it "nails" at "0" when focusing from infinity BUT at the closest "6" and up to "0" on the scale when focusing from the closest focus distance. For me this indicates some other problem, question is mechanical or optical.

/Claes-Ove

11-27-2022, 08:46 AM   #5
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QuoteOriginally posted by Paridon Quote
but with the DA16-50 it "nails" at "0" when focusing from infinity BUT at the closest "6" and up to "0" on the scale when focusing from the closest focus distance
Ok. I have never seen a lens/camera combo that bad. The DA16-50 did suffer from SDM focus drive problems, which would make it lazy, or fail altogether. With mine I had to "wake it up" when not used for a while, by manually moving the focus ring back and forth a few times while AF was engaged.
11-27-2022, 09:17 AM   #6
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I would not think it is a defective SD-Motor due to the fact that it is roughly 1 year since it was changed together with the board and I have not seen any tendences to "slow wakening up". What I have seen in ordinary shooting is some inconcistency in focus/sharpness.
Now it is to dark to do anything more today!
I will investigate furher later in the week and make some more "organized" tests to try to see what´s wrong. Focus, decentering or what.

/Claes-Ove
11-27-2022, 12:14 PM   #7
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I have seen more failed sdm lenses or “failing” than most. Some acted fairly normal but wouldn’t focus reliably. Screwdrive conversion helped in at least the two cases I remember. Those didn’t involve accuracy however. They involved failure to focus in challenging conditions (low light, poor subject for focusing, etc. )

11-27-2022, 09:50 PM   #8
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I would suspect a SDM motor issue; that can cause inaccurate focus, based on my my experience.
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