[p706]

I recently purchased a DA 35mm 2.4 to use with my Pentax Kr.
Shooting wide-open it was obviously back focussing. A few tests (not necessarily scientifically rigorous) and an AF fine adjustment of +6 seems to have solved it to my satisfaction.

But in changing this setting and then forgetting to reset it before mounting other AF lenses (Kr only has a global setting) I had a feeling that my 3 other AF lenses may also be benefitting from this setting.
I had probably not noticed the issue so much as I routinely stop down to around f8. Although there had been times I had blamed myself when focus was behind the subject.


I got the tripod back out and proceeded to test each of them. They all appear to focus more accurately with the +6 than without AF adjustment and as the 35mm is the only one I'd shoot with a large aperture it seems sensible to keep this setting. In my mind this is likely a small issue with the camera.

But now I attached a couple of manual focus lenses I am confused. Focus confirmation only seems accurate when disabling AF adjustment.
So the question I have is does the focus confirm when manually focussing work differently to the AF sensor (maybe similar to live-view?) or is there just some coincidence that my AF lenses need some calibration and my MF lenses do not?

[UncleVanya]

I'd vote coincidence.

[ramseybuckeye]

You do know that you can have the setting different for all AF lenses, or just that one, but it’s not affecting the manual focus lenses to my knowledge. If it does, then changing the setting for individual lenses should correct that.

[pschlute]

You do know that you can have the setting different for all AF lenses, or just that one, but it’s not affecting the manual focus lenses to my knowledge. If it does, then changing the setting for individual lenses should correct that.

The Kr has only one global adjustment.

---------- Post added 09-18-20 at 09:16 PM ----------

But now I attached a couple of manual focus lenses I am confused. Focus confirmation only seems accurate when disabling AF adjustment.

When a camera is made there is a tolerance in accuracy of the AF sensor vs the camera sensor itself. The AF/FA menu can be be used to correct this if it at the extremes. Every lens you mount on the camera is also capable of being in need of adjustment in itself. Indeed my experience shows that the same lens can AF differently depending whether it is focussing from infinity or nearest focus distance. This is more pronounced on the older screw drive AF mechanism.

From your observation it is likely that it is the camera that needs adjustment, not the autofocus lenses.

Now why do your Manual lenses not need this adjustment ? The only suggestion I have is that the green hexagon confirmation has a little bit of leeway. You will find that moving the focus ring a tiny bit after you have confirmation may still lead the camera to tell you the image is in focus. I think this is what you are seeing. Try an experiment by focussing from both extremes (infinity and near) and see if you get different results.

---------- Post added 09-18-20 at 09:20 PM ----------

So the question I have is does the focus confirm when manually focussing work differently to the AF sensor (maybe similar to live-view?)

No, the green hexagon takes its signal from the PDAF autofocus system, the same as when auto focussing using the viewfinder. The LV mode uses CDAF system which is entirely separate and does not require any adjustment at all

[ramseybuckeye]

The Kr has only one global adjustment.[COLOR="Silver"]

Thanks for the correction!

[UncleVanya]

You do know that you can have the setting different for all AF lenses, or just that one, but it’s not affecting the manual focus lenses to my knowledge. If it does, then changing the setting for individual lenses should correct that.

In addition to the Kr only having one adjustment, manual focus lenses on newer bodies vary in their ability to be identified uniquely. Only lenses with data communication can be identified enough to have individual adjustments. Most of the lenses this applies to are modern third party manual focus lenses.

[StiffLegged]

I found recently that AF adjustment was needed for an FA80-320 zoom but my old A series zooms focus accurately without adjusting the PDAF. So you’re not alone.

[p706]

Thanks all. This has been irritating to say the least.
Now when reviewing images where I failed to hit focus I have a huge temptation to re-test and try to improve the "DIY calibration".
I've done it twice now only to end up concluding exactly the same. I think if I reach a 3rd time I'll just accept my own limitations and stop trying to blame my equipment.

[p706]

Follow up. I traded in the Pentax Kr and upgraded to a used KS-2.
Focus peaking and the better viewfinder my main motivations (although when I aquire a WR lens that will also be very useful).

Of course now I have the ability to save calibrations for different lenses my DA 35mm 2.4 nails focus without changing anything.
I shall forget this whole epsiode!