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06-07-2017, 04:23 PM   #1
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Odd problem: DA 16-85 and Kenko (Tamron) Pz-AF 1.5x Teleplus SHQ

I just got a DA 16-85 and am enjoying it.
I also have the Kenko Pz-AF 1.5x Teleplus SHQ teleconverter, and mine is actually the highly regarded 1.4x Tamron version. I have been using it with my DA 18-135, and it works excellently with quick autofocusing and good results.

I am getting odd results using the Kenko TC with the 16-85.
  • Using the viewfinder (ie, PDAF), it works fine from 16 to ~55mm, but after that it is unable to get focus confirmation. It searches and tries to focus but can't. (And of course, I mainly would use this TC at 85mm, so it's a problem.)
  • Using LiveView (ie, CDAF), it works perfectly at all focal lengths.
I have tried at various apertures, distances, and have shot w/ plenty of light.

I've also made sure to clean all contacts with alcohol. (And the TC still works fine with the 18-135.)

Any explanation for what's going on? Any way to make it work? I can go to manual focus, of course, and I can use LiveView, though I prefer to use the viewfinder.


Thanks for any help/suggestions.

06-07-2017, 05:09 PM   #2
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Hypothesis - could it be that the 16-85 is a newer generation lens which for some reason isn't having a full conversation with the camera through the T/C's contacts? (I know my earlier generation non-AF T/C will communicate aperture control fully but will not dispatch focal length nor enable multi-point AF in the camera, and P-TTL flash doesn't handle well either.)

Other than that, I got nuthin' - they're both DC AF, so it isn't as if the 18-135 is falling back on screwdrive.
06-07-2017, 05:12 PM   #3
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Thanks, pathdoc. BTW, I had been having the issue using my K-3. I tried it out on my K-30, and the same thing happens.
06-07-2017, 05:18 PM - 2 Likes   #4
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QuoteOriginally posted by mgvh Quote
I just got a DA 16-85 and am enjoying it.
I also have the Kenko Pz-AF 1.5x Teleplus SHQ teleconverter, and mine is actually the highly regarded 1.4x Tamron version. I have been using it with my DA 18-135, and it works excellently with quick autofocusing and good results.

I am getting odd results using the Kenko TC with the 16-85.
  • Using the viewfinder (ie, PDAF), it works fine from 16 to ~55mm, but after that it is unable to get focus confirmation. It searches and tries to focus but can't. (And of course, I mainly would use this TC at 85mm, so it's a problem.)
  • Using LiveView (ie, CDAF), it works perfectly at all focal lengths.
I have tried at various apertures, distances, and have shot w/ plenty of light.

I've also made sure to clean all contacts with alcohol. (And the TC still works fine with the 18-135.)

Any explanation for what's going on? Any way to make it work? I can go to manual focus, of course, and I can use LiveView, though I prefer to use the viewfinder.


Thanks for any help/suggestions.
>F8 is probably just too dark for the AF to operate reliably, which is where you're at at the long end.


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06-07-2017, 05:52 PM   #5
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QuoteOriginally posted by Adam Quote
>F8 is probably just too dark for the AF to operate reliably, which is where you're at at the long end.
We have a winner! You're right, Adam. I just tried taking a picture of a light, and it worked at 85mm. I apparently need really good light for the PDAF autofocus to work.

It's still a little odd that the DA 18-135 works without issue, since it too is at f5.6 (> f8 or so w/ the teleconverter).
Thanks!
06-07-2017, 07:45 PM   #6
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I am not too sure that this is the full explanation. I believe that we see an example of a non-matching lens-converter pair. I have the same TC as theOP and have the same experience with my DA* 200/2.8(!) lens: It hunts for focus but won't lock. Only "remedy" is to push the AF button several times until it eventually locks.

Then I bought the Pentax 1.4 X AW converter, which per Pentax specifications is compatible with the DA* 200, and indeed: I have never had any problems with this pair. As I have said before, there are lenses and teleconverters, and then there are MATCHING lenses and coverters.

And I continue to be deeply impressed, that the Pentax engineers have managed to make their TC compatible with so many Pentax lenses, as the specifications tell us.
06-07-2017, 09:44 PM   #7
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QuoteOriginally posted by Stone G. Quote
I am not too sure that this is the full explanation. I believe that we see an example of a non-matching lens-converter pair. I have the same TC as theOP and have the same experience with my DA* 200/2.8(!) lens: It hunts for focus but won't lock. Only "remedy" is to push the AF button several times until it eventually locks.

Then I bought the Pentax 1.4 X AW converter, which per Pentax specifications is compatible with the DA* 200, and indeed: I have never had any problems with this pair. As I have said before, there are lenses and teleconverters, and then there are MATCHING lenses and coverters.
hmmm.... I tried being more persistent in pressing AF, and sometimes the focus would eventually lock in.
I do got focus confirmation in manual focus mode. Perhaps it is both the need for light and the compatibility of lens, tc, and camera that contribute to the issue.
Thanks.

06-08-2017, 08:34 AM   #8
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I've been shooting with the DA 16-85 and the Kenko Pz-AF 1.5x (actually 1.4x). Even in very bright sunlight, I can only sometimes get PDAF / viewfinder focus confirmation after repeated AF tries. It is rather frustrating. OTOH, using CDAF / LiveView works quite well and quickly.
Further, the results using the Kenko TC are noticeably better than using the lens alone and upsizing. (Using the Kenko TC with my 18-135 provided marginally better results.) In the attached photo, the 16-85 with the Kenko TC is on the left at 100% and the lens alone upsized to 140% is on the right. Using the Kenko TC does reduce the contrast, but that's easily fixable in PP. I don't know how well it shows in the attachment, but the detail / sharpness is significantly better w/ the Kenko TC.
So, with 16-85 and the Kenko TC, I'm able to extend my range to about 120mm.
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06-09-2017, 05:45 PM   #9
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QuoteOriginally posted by mgvh Quote
I've been shooting with the DA 16-85 and the Kenko Pz-AF 1.5x (actually 1.4x). Even in very bright sunlight, I can only sometimes get PDAF / viewfinder focus confirmation after repeated AF tries. It is rather frustrating. OTOH, using CDAF / LiveView works quite well and quickly.
Further, the results using the Kenko TC are noticeably better than using the lens alone and upsizing. (Using the Kenko TC with my 18-135 provided marginally better results.) In the attached photo, the 16-85 with the Kenko TC is on the left at 100% and the lens alone upsized to 140% is on the right. Using the Kenko TC does reduce the contrast, but that's easily fixable in PP. I don't know how well it shows in the attachment, but the detail / sharpness is significantly better w/ the Kenko TC.
So, with 16-85 and the Kenko TC, I'm able to extend my range to about 120mm.
Thanks for the report. I have the same TC.
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