[dr_Fell]

Hello,
I have read somewhere, that it is possible to adjust every AF point separately. Is that true?
My K-3 seems to have different FF/BF problem on side AF points (although it needs confirmation). I entered debug mode, but instead of seeing every AF point with its correction, I see "AF Area Test", "AF Area Number" and Focus correction that seems to be general and not intended for separate AF points.

Michael

[clackers]

Not as far as I'm aware, Dr Fell, where did you read that- got a link?

You may have a misaligned module in your K-3 - a warranty job if you detected this quickly enough after purchase.

[stevebrot]

I have read somewhere, that it is possible to adjust every AF point separately. Is that true?

If so, it is news on this site.

If you are seeing different behavior in the outlier AF points, that should not surprise you. They are not crosspoint and are only f/5.6 sensitive. In addition, lens optical aberrations may create issues at the edges that are not present at the center and which might affect both accuracy and precision at those points. Sharpness is also lower in those parts of the frame even when focus is good.

If you are needing to do fine focus for wide aperture shots in off-axis areas of the frame, manual focus in magnified live view might be a better option.

Are you able to provide an example of a photo where you believe focus was bad, your settings, and your expectations? Be sure to include if you were shooting hand-held. If not, how was the camera secured. Are you seeing consistent front or back focus or a mix at a particular point? Does it happen with all lenses or just one?


Steve

[Reed]

It is possible. But I don't recommend to do it. First of all-it will affect every lens you mount on your camera. Second playing with debug mode, if you don't have real good alignment target(at least LensAlign grade), technical experience and documentation for that mode its not very good idea. Keep in mind that side AF points are less sensitive and will not really be very reliable in low light conditions.
I have tested quite a few cameras reported to be faulty in terms of AF. To my experience 90% percent of auto focus faults are user or environment mistakes related, not because faulty camera, and most lens/camera kits have need very minor adjustments that sits well between consumer available range in normal camera menu.

[JimJohnson]

Personally, I'm wondering if there is some confusion between adjusting the AF points and adjusting AF front/back focus for individual lenses... adjusting AF points is decidedly something I have not heard of outside the repair bench, but adjusting AF front/back is inside the menu and debug mode is not needed unless the AF is way off (and personally I'd still send the camera in for servicing if that was the case.

[Reed]

When using adjustment aviable in normal menu- you adjust the algorithm for all focus points when paired with particular lens, or globally. But still it just software tweak. Debug mode menu offers different thing. Basically you change auto focus sensor factory tolerance values by some micrometers(μm), this is helpful when you can measure it properly and you are sure that camera is perfectly aligned with testing target. For example by placing it on self leveling optical rig, or at least using lens align tool. In perfectly lit environment. But, even slight misalignment, and light source change will affect precision of that tuning, and will do more harm than good.
Some older cameras, had also one risk in that menu- when some change was applied, the gauge was always set back to "0",for example when you did dial -50μmfor global, saved, and then switched to other menu- it was back to zero, but still the tune was dialed. This led to very uncomfortable situations when non aware users, decided to play with debug, and forgot from what point they ware starting the adjustments- making it virtually impossible to get back precisely to factory settings. And no-the factory reset was not helping. Probably re-flashing camera software would help.

[dr_Fell]

Thank You all!
Problem appeared when using Sigma 30.1,4 HSM, some side AF points have very consistent focus problems, while other didn't.
Recently I retested my body with Sigma 17-50 HSM (with DIY Lens align grade) and focus error was marginal/didn't exist (need to confirm, but it is possible that those errors were due to my problems with exact camera positioning and alignment).
Still, problems with 30 1,4 seem to be very consistent, some af points seem to focus very well, while others don't (does't matter if they are extra sensitive or not). I will do some more tests and post the results and examples here in few days.



Clackers, below are the links where I got that info from (or so I thought). Now I see it was probably a misunderstanding/overinterpretation on my side.

RiceHigh's Pentax Blog: K-3 Debug Mode and Menu

1. The debug menu enables af-adjustment for each auto focus point, These adjustments are added to the AF-Finetuning value.

and here: RiceHigh's Pentax Blog: K-x Debug Mode Tutorial - AF Adjustment

Btw, don't change the "AF Test" and "AF Area Number", keep them both at the default Zero 0. What I am interested is to adjust the central AF point only and to eliminate the Back Focusing tendency that I have encountered.

Problem appeared when using Sigma 30.1,4 HSM, some side AF points have very consistent focus issues, while other didn't. Recently I retested that with Sigma 17-50 HSM and focus error was marginal/didn't exist (need to confirm).

[Reed]

Can you share some pictures depicting that inconsistency or pictures from your tests?

[stevebrot]

Problem appeared when using Sigma 30.1,4 HSM

AF consistency with the Pentax version of that lens is a known issue that was discussed in the review here on PF

Sigma 30mm F1.4 DC HSM "Art" Review - Autofocus | PentaxForums.com Reviews


Sorry.


Steve

[Reed]

I've adjusted two copies of 30/1.4Art with USB dock station, both behaved excellent after adjustment. Do you have current firmware version in your camera?

[dr_Fell]

Hello Reed, sorry for answering so late. I had too many things on head. I unfortunately deleted those pictures. Meanwhile I had to send one of my K-3's for warranty replacement, then I calibrated 30/1.4 for that new body. So far everything seems perfect, maybe only most peripheral AF points have problems, but it seems it's normal with such bright lens.

The body that had problems with 30/1.4 is now working perfectly with my Sigma 17-50 (every AF point) .

Thank You all for answers, they were very helpful.

[Reed]

No problem Have fun with that stuff