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11-30-2014, 09:11 AM   #1
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AF of K-5 II with Sigma 17-70 Contemporary

Most of the time it is fine but this combo sometimes behaves very indecisevely even in good lighting conditions.

For example: I am focusing it on my hand after a landscape shot and it refocuses very smoothly and slowly going in right direction - for about 5 seconds without making huge jumps.

Seldomly the focusing stucks trying to make a small movement and making very quiet sounds.

Another problem - the camera "confirms" the focus even if focal plane is strongly in front of the location I point it at. This happened so oftenly at 17 mm that I gave 17-70 to service center to calibrate it but it changed nothing - the combo still oftenly strongly front-focuses and confirms the focus but after close-up refocusing and another refocusing it gets it. I could blame the lens but the body CONFIRMS the focus.

But: I almost never have problems with AF at bigger focal lengthes. I also did not have a single problem with screw-driven 17-70 F2,8-F4,5, being combined with same K-5 II it always focused fast and decisively (except when in very dim lighting conditions).


Share your thought on this please. I am really willing to change 17-70 to 17-50 F2.8 OS if it will change the AF.


Last edited by Casion; 11-30-2014 at 09:19 AM.
11-30-2014, 09:59 AM   #2
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I see quite a bit of fine dust on the mirror - could this be an issue?
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11-30-2014, 10:20 AM   #3
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Well you should keep your camera clean. Dust in the box can even show up in photos. But it would have to be really dusty to affect the AF. More important for AF is the lens and camera mount, they have to be free of grime and particles.
Secondly, are you using the latest firmware update on your camera? It is recommended that you use the latest one. Don't know about K-5II, but on some cameras it improved AF with certain lenses and conditions.
Thirdly, do you have AF micro adjust enabled? If your camera is consistently back or front-focusing, this Menu option can help. There are threads about focus calibration, with different techniques that you can use and even focus charts that you can order or print yourself.

I don't have experiences with the Sigma 17-70mm contemporary, but you can try searching for it in these forums, see if there are any other threads about AF problems and solutions.
11-30-2014, 10:30 AM   #4
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what focus setting do you use? do you select your own focus point or let the camera choose? If you choose focus point, there is no reason for the camera to confirm focus on something else other than that point.

12-01-2014, 11:25 AM   #5
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QuoteOriginally posted by Na Horuk Quote
Dust in the box can even show up in photos.
The dust is on the mirror. Sensor is kept clean by startup microjitter.

The second mirror and AF sensor lens are clean too.

QuoteOriginally posted by Na Horuk Quote
But it would have to be really dusty to affect the AF. More important for AF is the lens and camera mount, they have to be free of grime and particles.
They are fine.

QuoteOriginally posted by Na Horuk Quote
Secondly, are you using the latest firmware update on your camera? It is recommended that you use the latest one. Don't know about K-5II, but on some cameras it improved AF with certain lenses and conditions.
I believed that I do. However, I checked now, my firmware is 1.04 and there is .07 available. I will try reflashing it and will report about changes.

QuoteOriginally posted by Na Horuk Quote
Thirdly, do you have AF micro adjust enabled? If your camera is consistently back or front-focusing, this Menu option can help. There are threads about focus calibration, with different techniques that you can use and even focus charts that you can order or print yourself.
I do not always adjust AF but when I do I don't use charts. I prefer finding a shining object and judging about AF shift by the colour of fringing of this object.

As I said, the AF error is not persistent so adjustment is not helpful.

QuoteOriginally posted by aleonx3 Quote
what focus setting do you use? do you select your own focus point or let the camera choose?
Manual single point selection.

QuoteOriginally posted by aleonx3 Quote
If you choose focus point, there is no reason for the camera to confirm focus on something else other than that point.
I would be happy believing in it too but Pentax firmware is far from ideal and I am really not surprised. As I said, there were zero problems with screw-driven 17-70.

Slightly related: I previously thought that camera should count wheel clicks precisely but Pentax thinks differently. It counts fast wheel clicks at 1/3 rate.

---------- Post added 12-01-14 at 22:58 ----------

After 1.07 update the focusing is still sometimes very uncertain at ~17-24mm (slow motor speed and whistling sounds) and very good at any bigger focal length.

I will see if strong front focus still occurs in next days.

Last edited by Casion; 12-01-2014 at 12:04 PM.
12-04-2014, 01:15 PM   #6
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So far I have not expirienced any front focusing issues, new firmware fixed them.

But this slow indecisive focusing persists. Is this an HSM issue? Does anybody else expirience it with any HSM objective?
01-11-2015, 08:54 AM   #7
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I cannot believe that noone can either confirm issues or say that everything fine. I really need your expirence, please express yourself!

QuoteOriginally posted by Casion Quote
So far I have not expirienced any front focusing issues, new firmware fixed them.
Update: new firmware replaced them with backfocusing. So it essentially fixed nothing.
01-11-2015, 09:06 AM   #8
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Are you sure your problems are not related to the SR problem at wide angles with this lens that has been confirmed by several people on this message board?

01-11-2015, 10:07 AM   #9
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QuoteOriginally posted by IchabodCrane Quote
Are you sure your problems are not related to the SR problem at wide angles with this lens that has been confirmed by several people on this message board?
Yes, I am perfectly sure in that.

I have expirienced some problems with SR at short end and disabled it permanently. Also: questionable photos were made in summer daylight.
01-17-2015, 10:19 AM   #10
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I also have no problems with separating OOF blur from motion blur and I also watch the position of focusing ring when the misfocusing happens.

Last edited by Casion; 01-17-2015 at 10:31 AM.
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