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08-13-2019, 05:35 AM   #1
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DA 50-135 and autofocus

Dear All,

I wuold like to have some suggestions.

I used K70 and 50-135 for model shots, It missed some photos. They are clearly out of focus.

My questions are:

Does the 50-135 perform in a better way in another camera? (k3, kp ,...)

Is there a particular setting that can help the k70 to focus the subject?

Are there alternative over the 50-135?

Many thanks

Davide

08-13-2019, 05:42 AM   #2
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Did you try using live view? Have you carefully calibrated the focus? What f stop? Can you post some examples? Is the lens converted to screw drive?
08-13-2019, 05:55 AM   #3
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Did you try using live view? No

Have you carefully calibrated the focus? No, Because other photos are in focus

What f stop? 2.8

Can you post some examples?, yes asap

Is the lens converted to screw drive? No

Many thanks

Davide

Read more at: DA 50-135 and autofocus - PentaxForums.com
08-13-2019, 06:07 AM   #4
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First I would calibrate focus at the distance and focal length that you will need the most critical focus from.

If workflow permits, live view is the best chance for accurate focus. Pdaf has problems with zoom lenses for to minor shifts in the focus at various focal lengths.

Screw drive conversion can sometimes help. However your lens' symptoms as described don't seem to fit that pattern. I've converted at least a handful of 50-135s that seemed to have focus issues (failure to lock focus) and after conversion the tentative hesitant focus was decisive and more accurate.

08-13-2019, 11:23 AM - 1 Like   #5
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QuoteOriginally posted by Davidex Quote
Have you carefully calibrated the focus? No, Because other photos are in focus
I think the question to ask is if you use AFA, AFC or AFS?
Second question to ask is, when you see the subject in the viewfinder, do the focus point cover the subject area of focus during the whole time when the camera is focusing the lens on the subject?
Usually, Pentax AF.S lock is very repeatable, but it is when the subject moves between the time of focusing and the time of exposure than leads the subject to be out of focus. When I understood this, I never had a picture out of focus again.
08-13-2019, 02:58 PM   #6
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I have a K-3ii and a recently purchased used Da 50-135 that is in mint condition and i knew the person that bought it from new so i know it was in perfect condition and i run into the same problem. I have calibrated the focus but at times it just flat out misses focus, i fully understand the shallow depth of field this lens can produce and i am very careful about moving the camera or the subject moving. I tend to use AF. S. and the center focus point with the viewfinder, sometimes it misses to the point it can clearly be seen in the viewfinder and yet i get focus confirmation from the camera? Live view works well but there are times when that is a little too slow. I kinda wish the SDM would quit so i could convert it to screw drive..
08-13-2019, 04:11 PM   #7
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Hi Davidex,

Can you post samples with the EXIF intact? Otherwise it's not possible for someone to see if you're doing something wrong, or if the lens needs you to calibrate it with your camera.
08-13-2019, 05:12 PM   #8
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Are you using the centre focus point and re-composing, or shifting the focal point to suit your framing?

08-14-2019, 06:39 AM   #9
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QuoteOriginally posted by Davidex Quote
Dear All,

I wuold like to have some suggestions.

I used K70 and 50-135 for model shots, It missed some photos. They are clearly out of focus.

My questions are:

Does the 50-135 perform in a better way in another camera? (k3, kp ,...)

Is there a particular setting that can help the k70 to focus the subject?

Are there alternative over the 50-135?

Many thanks

Davide

What Auto focus setting were you using?
As in Center, Selected point or camera chosen AF point?
08-14-2019, 07:44 AM   #10
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QuoteOriginally posted by shardulm Quote
What Auto focus setting were you using?
As in Center, Selected point or camera chosen AF point?

I used center focus point and AF.C.

---------- Post added 08-14-2019 at 07:46 AM ----------

QuoteOriginally posted by Sandy Hancock Quote
Are you using the centre focus point and re-composing, or shifting the focal point to suit your framing?

I used centre focus point without re-composing. The models were to quick
08-14-2019, 08:59 AM   #11
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The 50-135 is a great lens, but is slow to focus.

What were the models doing when you shot? You said 'The models were to quick' which suggests possibly fast movement?
08-14-2019, 10:35 AM   #12
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QuoteOriginally posted by Davidex Quote
I used center focus point and AF.C
Oh, so where are the pics, David? We need to diagnose.

Did you just point at a person and not a line on the person?



08-22-2019, 04:41 PM   #13
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QuoteOriginally posted by Davidex Quote
I used center focus point and AF.C.

---------- Post added 08-14-2019 at 07:46 AM ----------




I used centre focus point without re-composing. The models were to quick
With AF-C, the shutter will release even if focus is not achieved. This is often used when burst shooting fast action subjects and not using center-only AF point, so if the subject has moved off-center to another focus point, the camera can still possibly grab onto the subject anyway. Some shots may not be in focus while others will.

If using center only spot focus point, and using AF-S, you must be good at panning or following your moving subject. The shutter will not fire unless focus is achieved, but then it is possible for the subject to move out of focus during the shutter firing process, so it is more up to your skill in panning. Using an adequately fast shutter speed for moving subjects is also essential.
08-22-2019, 05:49 PM   #14
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QuoteOriginally posted by bschriver11 Quote
I have a K-3ii and a recently purchased used Da 50-135 that is in mint condition and i knew the person that bought it from new so i know it was in perfect condition and i run into the same problem. I have calibrated the focus but at times it just flat out misses focus, i fully understand the shallow depth of field this lens can produce and i am very careful about moving the camera or the subject moving. I tend to use AF. S. and the center focus point with the viewfinder, sometimes it misses to the point it can clearly be seen in the viewfinder and yet i get focus confirmation from the camera? Live view works well but there are times when that is a little too slow. I kinda wish the SDM would quit so i could convert it to screw drive..
I have converted a LOT of DA* 50-135 lenses. Even when SDM appears to work I have had a few customers with weird focus problems ask me to convert their lenses. To my surprise these have all been improved by conversion. That is not true of my own copy which focuses fairly well - albeit slower than I want sometimes. The accuracy of some of these lenses had deteriorated - one lens would not focus in low light - but worked fine with bright light until converted to screw drive. My suspicion is that the method of focus feedback from the lens starts to break down when SDM is weak and the lens is signaling that it is making fine movements it may not be actually making and the camera gives up. I assume the low light made this more obvious by making the camera want more adjustment to be certain of focus. This is just speculation however. I can only say that in most cases converting from SDM to screw drive doesn't really affect much in terms of speed or accuracy, but sometimes the SDM has hidden problems. New or old doesn't really matter we don't really have a full handle on which lenses die and which don't. And we have even less data on why some need conversion to be accurate. I wouldn't have actually believed it - if I hadn't seen the results on multiple customer lenses.

The point is - you MAY want to convert it and see if it helps. Speed and/or accuracy can improve if the SDM is slower than it is supposed to be - but how you can tell that without multiple points of comparison except by converting and testing I have no idea. However the lens is never going to be lightning fast.
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