[Larrymc]

I had a thread about this problem a long time ago, and "we" felt it was a bug. Nobody offered the solution you present here. Very good to know!

And no, you don't lose focus if you release the back button before you shoot, because pressing the shutter release has no effect on AF, and there is nothing else that will cause the lens to refocus.

Nope its not a bug, I can't recall anywhere in the manual this is discussed but I think there is info on the Pentax Japan web site discussing this. I puzzled over it for quite a while and why the AF point would show in AF-C, then I started testing by holding the AF button down while releasing the shutter and Voila the point in focus showed up in the Exif data of EXIFToolGui. I still occasionally have a bit of brain fade and release the AF button before releasing the shutter.

[stevebrot]

I puzzled over it for quite a while and why the AF point would show in AF-C, then I started testing by holding the AF button down while releasing the shutter and Voila the point in focus showed up in the Exif data of EXIFToolGui. I still occasionally have a bit of brain fade and release the AF button before releasing the shutter.

Point in focus only shows if AF is active and focus acquired, IIRC.


Steve

[Larrymc]

Point in focus only shows if AF is active and focus acquired, IIRC.


Steve

AF is active as long as the AF(back button) is held in after focus is acquired.

[stevebrot]

The downloaded image clearly shows motion blur: look at the sunglasses and shoes.

I looked at the necklace.

There is an anomalous aspect to the EXIF...

Code:

Subject Distance Range : Close
.
.
.
Focus Range Index : 2

The lens reports these values based on the focus ring rotation and "2" for focus range index is under 5 feet distant which is somewhat closer than the apparent distance to the subject in your photo even at 23mm. For bad.jpg, the focus was not proper to the subject.


Steve

---

Last edited by stevebrot; 12-13-2018 at 11:25 PM.

[bxf]

I looked at the necklace.

There is an anomalous aspect to the EXIF...

Code:

Subject Distance Range : Close
.
.
.
Focus Range Index : 2

The lens reports these values based on the focus ring rotation and "2" for focus range index is under 5 feet distant which is somewhat closer than the apparent distance to the subject in your photo even at 23mm. For bad.jpg, the focus was not proper to the subject.


Steve

I've often wondered about the meaning of some of the info in the metadata, so this helps.

So now the question becomes, why would the focus be so far off (subject was definitely much more than 5 feet away)?

I looked more and I see that the bad shots (2,3,4,5,6) show Focus Range Index of 7, 4, 3, 2, 2 respectively - all over the place, but the focal lengths and distances change, so one can't make clear conclusions about the validity of these values. Having said that, Shots 1 and 2 were taken 18 seconds apart, both at 16mm, and #1 says "Close", #2 says "Distant", yet it is clear from the images that I moved closer to the subject for the latter.

So, something is screwed, but I don't know what. Perhaps next time I'll intentionally not wait for the AF confirmation, and we'll see what happens.

[stevebrot]

so one can't make clear conclusions about the validity of these values.

All you can conclude is that the lens returned those codes to the camera when polled. On my K-3, this happens with my AF lenses whether or not AF is turned on and whether or not the lens is in focus.* With the focus ring at infinity it reads 7 (very far) and at MFD, 0 (very close); EXIF:SubjectDistanceRange returned "distant" and "macro" respectively.** I don't have any lenses where the focus ring does not rotate, so don't know the behavior for that case.

Is there any chance that the focus ring might have been jostled? According to the in-depth review on this site, the DA 16-85 has a very short throw for manual focus and/or quick-shift and the risk of jostling focus was noted in the review.

HD Pentax-DA 16-85mm F3.5-5.6 Review - Focusing | PentaxForums.com Reviews

Whether your strange results are related to the EXIF is hard to tell. It may be there is an internal problem in the lens that is causing both.


Steve

* All KAF(n) lenses support polling of lens state through the data pin on the mount face.

** I use ExifTool and tags within the makernotes section are the author's best guess as to names and functions. Those assignments are deemed "reliable, but not guaranteed", though agreement with standard EXIF tag values is a strong vote of confidence.

[bxf]

Is there any chance that the focus ring might have been jostled? According to the in-depth review on this site, the DA 16-85 has a very short throw for manual focus and/or quick-shift and the risk of jostling focus was noted in the review.HD Pentax-DA 16-85mm F3.5-5.6 Review - Focusing | PentaxForums.com Reviews

Not likely, five shots in a row, followed by dozens more, with only two (I said "one" previously) similar (and again consecutive!) failures.

For now, I will assume that I failed to wait for AF confirmation, though I'm not betting on this. Perhaps subsequent outings will shed some light on this. Now that I know there is a possible problem, I can check each shot carefully.


Thanks for all input.

[stevebrot]

Not likely, five shots in a row, followed by dozens more, with only two (I said "one" previously) similar (and again consecutive!) failures.

Try it with one of your other lenses.


Steve