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01-08-2019, 11:22 AM   #1
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Pentax k5II aufocus issues

Hello pentaxians,

I have k5II, had k-x long time ago. But when focusing with k5II i have feeling that autofocus not right. Had same feeling with k-x.

let me explain: i understand how autofocus and autofocus correction works, calibrated all my lenses, all needed little corrections. But when distance to object i want to focus at changes i need different focus corrections. Same trouble seen when using 2 different 35mm f2,4 , even had same problem with 50mm f1,8. for example im taking portrait at distance of 2 meters i need +3 correction. if subject moves 6 meters and i want take full body shot, i need +6 correction.
if shooting liveview its ok, camera autofocus is fine.

it is normal? had same problems with other pentax cameras ?

01-08-2019, 12:30 PM   #2
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How did you test for the required correction value? If this is not done right, it can backfire. It is normal for many lenses to require corrections, but it varies from body to body. However, the behavior you're describing may also imply a problem with the camera itself.
01-08-2019, 12:49 PM - 1 Like   #3
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When I first read your post, I thought that Focus Shift was a culprit, however that is typically a trait that is specific to a lens based on the curvature of the glass and I haven't heard of cases where Focus Shift is observed with the 35mm and 50mm.

Lens Calibration can be a pain and it is often times subjective. Some best practice with shorter focal distances is to take the focal length and multiply it by a value between 25 and 50. In this case, using your 35mm and multiplying by 50 will give you '1750'. Take that mm value and convert it to ft will give you a distance of 5.74.

That distance (5.74) is the amount of space you will want to have between your lens and the target you are using for calibration. Some additional tips:
- target must be well lit
- turn OFF image stabilization
- shoot at the widest aperture available
- shoot at a lower ISO
- shoot with a shutter speed equal to or greater than the max focal length to mitigate shake and increase sharpness
- use single point focus

Depending on if your target has a ruler or if you are using something stationary, check if you are front or back focused and compensate in intervals of 5 taking MULTIPLE shots to account for user error. Keep increasing that number until you reach expected focus that is inline with your single point focus target.
01-08-2019, 02:43 PM   #4
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My initial thought was what focus method are you using? If you are using single point autofocus, there may be a camera problem. If you are using auto, then the camera could be changing the focus point making you think distance is changing the needed correction.

01-17-2019, 10:10 AM   #5
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Focus adjustment can change with subject distance, but on a 2.4/35 this effect should be negligible assuming that you corrected properly. Without a good correction to start with on sloping ruler, you may be off without knowing.
Rembering my K5, correct focus also depended on light conditions. Indoors and with tungsten I had a lot of trouble. The effect was gone with K3, I donīt know about K5ii.
01-18-2019, 02:09 PM   #6
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Seems like probable inaccuracy of calibration in this case. Accurate AF is also a property of the lens, but these two primes have a good reputation on virtually any camera body.

As to the worst scenario with the original K-5 and tungsten light, I had problems with it especially when using certain lenses. I don't recall any issue at all with my K-5IIs, but recently decided to take my original K-5 for a wrestling tournament shoot, and using my very reliable DA 18-135mm lens. No problem at all with this lens on the K-5, even in tungsten lighting!
01-18-2019, 06:39 PM   #7
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This is why newer Tamron and Sigma lenses allow one to adjust based on several distances per focal length.


And when you shoot with live view you're taking the AFMA out of the equation.

My suggestion would be to find the middle and adjust for that. Or simply adjust for the distance most used. But I haven't seen it be an issue with a 35mm on crop (equivalent 52ish view angle).


Also make sure you're not focusing then recomposing before taking the photo. That can make your shots slightly out of focus as your angle to the subject changes. Better to move the focus point with the D pad on the back over the subject and keep the camera in position.
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