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06-12-2019, 01:27 AM   #1
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Pentax FA* 300mm f2.8 Back focus issues

Hi Forum,

I have recently purchased a Pentax FA* 300mm f2.8 secondhand from a dealer in Germany. It is a lovely lens and I am very fond of it. However the lens have severe back focusing issues when using auto focus.

I have tried to correct this using the in camera autofocus correction on my Pentax K3 body. The adjustment range on this camera is not sufficient to fix the issue.

Using debug mode I have adjusted the camera autofocus and this combined with a autofocus correction of +8 has resolved the issue. Unfortunately the corrections made in debug mode now cause my other lenses to have front focus issues.

I have contacted my local Pentax service center (I live in Denmark so my closest center is in Sweden) and asked if they could calibrate the lens. I received the following reply, " Sorry your lens is to old so it canīt be adjusted."

Now my question is this:
Is it true that this lens cannot be adjusted for back focusing issues?
What would you guys do? I have a 30 days full refund return option on the lens. However I like the lens, and it is not likely that I will come across another one anytime soon.
Are there any other options I should consider?


Last edited by Blue; 06-12-2019 at 11:55 AM. Reason: removed weird hotlink
06-12-2019, 05:50 AM   #2
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You'd probably have to find an independent repair person who can calibrate it. If you really are planning heavy usage of this lens however, for the cost and hassle maybe just dedicate this body that you've already got calibrated to work and get a second body for your other lenses. (If you keep the lens, try to get at least a partial refund to offset repair costs.)
06-12-2019, 07:33 AM   #3
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I have similar problem with my copy of FA*300 f2.8. The lens does not focus to infinity either (maybe up to 400 meters).
I gave the lens to one person with optical tests bench and he tried to fix the issue but the result is that the infinity focus issues is still present as is the back focusing but additionally it will not focus correctly any more with TC1.7AF converter.
So, it's a little bit worse than it was before.

I may try one more place to see if they can fix it but then I'm done - I'm currently using the Pentax DFA150-450 for wildlife (some times DFA*70-200 also) and the 300 has been collecting dust...
06-12-2019, 07:41 AM   #4
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I wonder if you have a filter in the rear holder? It may actually need it. Try with/without UV filter and see if there is a difference.

06-12-2019, 09:59 AM   #5
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QuoteOriginally posted by vonBaloney Quote
I wonder if you have a filter in the rear holder? It may actually need it. Try with/without UV filter and see if there is a difference.
Well that's something I didn't even think of. Need to go and buy one to check it out...
06-12-2019, 11:39 AM   #6
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I have tested both with and without a filter in the rear holder. To me it made no difference in the autofocus.

Can anybody recommend a service facility in Europe that will be able to calibrate the lens?

Last edited by Blue; 06-12-2019 at 11:56 AM. Reason: Removed weird hot link in signature
06-12-2019, 12:41 PM   #7
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It has a defect if more than +10 is needed.

Refund in my opinion!

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