[sebberry]

Playing around with my DA* 50-135 (Screwdrive, NOT putting a 4th SDM motor in it...).

I've had to set the AF fine tuning to -5 on it. Manual spot focus, tripod mounted, it reliably focuses on my very patient Paddington Bear test model. Flipping it to LV, however, and it's another story. Simply far too out of focus to be useful.

Also noticed this on my Sigma 18-300 set at 135mm that doesn't require any AF fine adjustments.

Any thoughts on the discrepancy? I was selecting the focus point exactly in the same spot for each test.

[Mooncatt]

Something isn't adding up.

If you lock auto focus with the OVF and take a photo, the photo is in focus?

When you lock focus and switch to LV, are you re-confirming focus lock in LV?

If not, what happens if you do?

Locking focus in LV should work 100% of the time because you're using the sensor itself to achieve focus. AF fine tuning doesn't affect this at all. Fine tuning only adjusts the focus when using the OVF, because you're using a separate sensor for that. If anything, I'd expect your results to be reversed, with LV in focus and OVF out of focus.

[sebberry]

Something isn't adding up.

Welcome to Pentax AF...

If you lock auto focus with the OVF and take a photo, the photo is in focus?

Yes.

When you lock focus and switch to LV, are you re-confirming focus lock in LV?

I re-focus. Without moving the focus point, the camera slightly re-focusses the lens. Taking the photo and it's OOF.

If not, what happens if you do?

Locking focus in LV should work 100% of the time because you're using the sensor itself to achieve focus. AF fine tuning doesn't affect this at all. Fine tuning only adjusts the focus when using the OVF, because you're using a separate sensor for that. If anything, I'd expect your results to be reversed, with LV in focus and OVF out of focus.

Here's a quick video from my phone. Should be pretty clear what I'm doing there. You can definitely see that after I switch to LV, the screen appears to show an in-focus image. After auto-focusing, it's OOF.

You Tube

You Tube

Edited to add: If I switch to LV and re-take the photo as it was focused in OVF without re-focusing, it is in focus.

[pschlute]

It looks like nothing is in focus at all in the LV picture.

Can you see from looking at the distance scale on the lens, where the camera thinks it is focussing in LV compared to OVF...... ie is it focussing longer or shorter ?

[Medex]

What camera are you using?
I found that KAF4 lenses (DFA*50 and *85) do not focus properly in LV on K-5/5ii camera. Always slight back focus. Still normal AF in OVF mode. Maybe conversion to screw drive changed somehow the AF performance in LV mode?

[BigMackCam]

What camera are you using?
I found that KAF4 lenses (DFA*50 and *85) do not focus properly in LV on K-5/5ii camera. Always slight back focus. Still normal AF in OVF mode. Maybe conversion to screw drive changed somehow the AF performance in LV mode?

It's the K-3III (we're in the Pentax K-3III section of the forums ) and the DA*50-135 (as mentioned in the OP's first post)...

[Medex]

It's the K-3III (we're in the Pentax K-3III section of the forums ) and the DA*50-135 (as mentioned in the OP's first post)...

Thank you.
I just want to say that sometimes focus in LV is not 100 percent accurate. In opposite I thought always before I found this issue.

[UncleVanya]

Contrast detection requires a certain level of contrast to work. It may eliminate some focus errors but it isn’t always accurate due to other factors. Lighting and subject can negatively impact accuracy. However I get the impression the 18-300 at 135 worked accurately in both liveview and ovf in the same testing arrangement? I’ve never seen this level of inaccuracy myself in Pentax or any other brand’s contrast detection results myself.

Did you do your screwdrive conversion yourself? I just wonder if the file was improperly edited as the numbers inside it affect focusing reliability. There were some users who mistakenly used the wrong file (from another persons lens) causing issues for themselves. As long as you used the original file and only modified the correct items your lens should focus reliably as before (or better).

I’d suggest another test with a different target. Or pick a different point on the target like the words that has very good contrast.

[Mooncatt]

Welcome to Pentax AF...

Touché, lol.

Here's a quick video from my phone. Should be pretty clear what I'm doing there. You can definitely see that after I switch to LV, the screen appears to show an in-focus image. After auto-focusing, it's OOF.

January 10, 2022 - YouTube

It looks like the camera looses the focus lock just before the shutter releases. When I slowed the video to half speed, I can see it indicates a lock for a split second, then the indicator goes away before the shutter releases, as if the camera realizes it doesn't have a lock. Have you checked to make sure the contrast AF priority is set to focus lock and not shutter priority? Being on shutter could cause it to release without being in focus.

I would try using other subjects and better lighting to see if results improve. On my mkII, I notice significantly better accuracy in OVF mode, and LV is prone to hunting unless I have a lot of light and great contrast. I try not to use it unless I'm setting up a static shot and using manual focus. The black on brown may be close enough to throw it off.

[sebberry]

I was wondering about the screw drive vs SDM for accuracy, but I was able to reproduce the same thing using my Sigma 18-300 DC.

Mooncatt, I was using Back-button AF, no focus on the shutter button so I did lock focus before taking the shot

Maybe I'm getting overly picky and I'm trying not to have any regrets with this purchase. So far my luck with Pentax is repeated dead SDM motors in my 50-135, my 16-50 has a dead SDM motor, I had a 540FGZ flash that bit the dust after very little use and of course all the focus issues...


I'll give it another try later tonight.

[sebberry]

I was shooting wide open and under a halogen light.

I'll try again with another higher contrast target and in different lighting but this isn't something that it should be missing - I feel like I'm making up excuses to defend and justify the camera. Oh the light isn't perfect, oh the target isn't contrasty enough... heaven help me if I want to take an indoor photo

[sbc]

I had a Pentax lens that does that on my K-5IIs. OVF focusing was fine but misfocused on LV. On the K-3III, it focused fine with OVF but cannot lock focus with LV.
So I am certain it is your lens that is the problem.

[sebberry]

I repeated the test using a different test subject.

I lined up 4 batteries, white body with black text. Can't get any more contrasty than that.

Set up the camera at a 45 degree angle to the batteries, aligned the batteries so the text was facing directly at the camera. Batteries named 1-4, left to right.

First with the K3-3 in OVF - 50-135 @ 2.8 @ 102mm
Shot batteries 1-4 in order, center point focus, re-focusing on each and each was in focus. No front or back focusing.

Repeated the test in LV - Battery 1, back-focused and battery 3 ended up being in focus in the image. Battery 2 - back-focused and battery 4 ended up being in focus. Battery 3 and 4 both back focused with nothing in clear focus.

Conclusion - K3-3 with the 50-135 with -5 on the AF fine calibration consistently hits focus in OVF, center point. In LV, it's back-focusing.

Is it the lens?
I repeated the same test on my K5 and the LV focus performance was much more acceptable.

One would have a hard time figuring out how the contrast detect focus algorithm would screw up the focus in LV.



Here's a puzzling bit.

Same test with my FA50 @ F/2.0.
Focused on - result
Battery 1 - in focus
Battery 2 - front-focus with battery 1 in better focus than battery 2
Battery 3 - in focus
Battery 4 - in focus

I could not get the camera to focus on battery 2, despite the other 3 being OK.

In LV:
Focused on - result
Battery 1 - slight back-focus
Battery 2 - in focus
Battery 3 - back-focus, # 4ended up in focus
Battery 4 - in focus


I won't post them all here, if someone wants to look through them all I can upload them to Flickr
Attached are two photos with the 50-135 on the K3-3, focused on the second battery from the left. The one that is in focus (second image) is the OVF focused image.

[Kobie]

Did you recently do a firmware update? I had a similar issue after doing firmware updates. I had to reset the lens focus correction (only for that one lens) back to 0, then did a factory reset. Then re did focus adjustments and both live view and OVF are good. Nothing else worked until I reset to 0 and reset the camera.

[licht96]

I didn´t read the whole comments here - I just saw the headline and the video. May be someone mentioned it already.

Did you check the other AF possibilities for Live view?
It seems you´re using the "tracking" one (more or less AF-C for Live view). May be it doesn´t like the not moving target or not moving camera***
Is there a difference using small or medium focus pont/area of the other AF possibilities?

***With the older cameras I was disappointed with the old tracking in live view as well, when I realized, that it is not really comparable to the AF-C in OVF since the lens was not really reacting in the right manner to changing distance