Pentax FA* 300mm f2.8 Back focus issues

Mikkel128 · 06-12-2019, 01:27 AM

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 can´t 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

vonBaloney · 06-12-2019, 05:50 AM

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.)

**reytor** · 06-12-2019, 07:33 AM

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...

vonBaloney · 06-12-2019, 07:41 AM

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.

**reytor** · 06-12-2019, 09:59 AM

Originally posted by vonBaloney

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...

Mikkel128 · 06-12-2019, 11:39 AM

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?

**clackers** · 06-12-2019, 12:41 PM

It has a defect if more than +10 is needed.

Refund in my opinion!

angerdan · 09-09-2020, 06:02 AM

Originally posted by Mikkel128

I have tested both with and without a filter in the rear holder. To me it made no difference in the autofocus.

How's your lens topic now (a year later)?
How did you test the focus?
Did you use an tripod?
Which light source did you use?
Which distance did you test?
And on what camera model did you test the FA* ?

Take a look at my thread:
FA* 300mm 2.8 ED IF - thread collection - everything about the FA300/2.8 - PentaxForums.com

Mikkel128 · 09-10-2020, 09:53 AM

So here one year later. I still do not get the images that I want from this lens. It may be an issue with the lens or my skills as a photographer. I hope it is the later, because it will likely be cheaper to correct.

Regarding the focus issue. I did a lot of testing with this lens and it turned out that there was an issue´with my Pentax K3 camera. On my fathers K70 the lens required a +8 correction. I got the same result when I purchased a K1 and this is in line with what other reports for this lens. I used a focus chart at 30 meter distance in bright sun light for the tests.

I took the lens out the other day. Attached is a sample picture. I have included som close ups to highlight the issues I am having. If anyone have any suggestions I would love to hear them!

This picture was taken on an overcast day with some sun. When I look at the closeup from the image I see some chromatic aberration. I am not sure if it is worse than expected. It does get get bad if I do not stop down the lens a little.

My main issue is with the out of focus area. If you look at the face of the wicket keeper (the guy with the blue cap). The white logo on the cap looks like it has a second outline. Rather than a nice blur, it looks like two images superimposed on one another.

What do you guys think? Am I being too picky or is there an issue with my lens?

Best regards,
Mikkel

**luftfluss** · 09-10-2020, 12:26 PM

I think because the white logo was over-exposed, the contrast between it and the darker cap may be what's causing the harsh outline. I think older lenses tend to struggle in this scenario more than modern lenses do.

The lanyard around the wicket keeper's neck also has a bit of a "double edge".

Edit: Interestingly enough, in a thread started by @angerdan there is a comment that the FA* 300/2.8 "is somewhat prone to fringing". https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/354675-sig...ml#post4118746

angerdan · 09-12-2020, 04:11 PM

Originally posted by Mikkel128

So here one year later. I still do not get the images that I want from this lens. It may be an issue with the lens or my skills as a photographer. I hope it is the later, because it will likely be cheaper to correct.
I took the lens out the other day. Attached is a sample picture. I have included som close ups to highlight the issues I am having. If anyone have any suggestions I would love to hear them!
What do you guys think? Am I being too picky or is there an issue with my lens?

How's the image quality with static scenes and CDAF (LiveView) ?
Which AF point did you use?
Is the rear filter in place?

Mikkel128 · 09-23-2020, 05:06 AM - **1 Like**

Hi All,

I took the lens out for a new test and this time I removed the front UV filter from the lens. This seems to have made a difference in the image quality. Here is a sample picture from the day taken with the lens wide open.

I have tried cleaning the filter, and it looks clearer now. I think I might have to purchase a new filter to make sure the coating has not been damaged by my cleaning attempts or by the previous owner.

(The picture is from the national U15 championship in Cricket in Denmark. The batsman was given out "Stumped", in case you were wondering)

**clackers** · 09-23-2020, 04:21 PM

Throw away that UV filter, Mikkel. It serves no protective purpose that a lens cap doesn't do better, and it can only ever degrade, not improve, the image quality you've paid for!

I hope your picture was used as evidence that a millimetre of the batsman's right foot is behind the line, should be not out. (I'm a cricketer myself)

06-12-2019, 01:27 AM	#1
Mikkel128 Junior Member Join Date: Jun 2019 Location: Gladsaxe Posts: 29	*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 can´t 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, 11:39 AM	#6
Mikkel128 Junior Member Join Date: Jun 2019 Location: Gladsaxe Posts: 29 Original Poster	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

09-10-2020, 12:26 PM	#10
luftfluss Site Supporter Join Date: Jun 2011 Location: NJ Photos: Gallery \| Albums Posts: 11,628	I think because the white logo was over-exposed, the contrast between it and the darker cap may be what's causing the harsh outline. I think older lenses tend to struggle in this scenario more than modern lenses do. The lanyard around the wicket keeper's neck also has a bit of a "double edge". Edit: Interestingly enough, in a thread started by @angerdan there is a comment that the FA* 300/2.8 "is somewhat prone to fringing". https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/354675-sig...ml#post4118746 Last edited by luftfluss; 09-10-2020 at 12:31 PM.

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06-12-2019, 05:50 AM	#2
vonBaloney Pentaxian Join Date: Oct 2011 Location: Albuquerque, NM Posts: 6,029	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
reytor Site Supporter Join Date: Aug 2009 Location: Santiago Photos: Gallery Posts: 220	I have similar problem with my copy of FA300 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 DFA70-200 also) and the 300 has been collecting dust...

06-12-2019, 07:41 AM	#4
vonBaloney Pentaxian Join Date: Oct 2011 Location: Albuquerque, NM Posts: 6,029	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
reytor Site Supporter Join Date: Aug 2009 Location: Santiago Photos: Gallery Posts: 220	Originally posted by vonBaloney 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, 12:41 PM	#7
clackers Otis Memorial Pentaxian Join Date: Jul 2013 Location: Melbourne Photos: Albums Posts: 16,397	It has a defect if more than +10 is needed. Refund in my opinion!

09-09-2020, 06:02 AM	#8
angerdan Pentaxian Join Date: Feb 2015 Photos: Gallery \| Albums Posts: 2,643	Originally posted by Mikkel128 I have tested both with and without a filter in the rear holder. To me it made no difference in the autofocus. How's your lens topic now (a year later)? How did you test the focus? Did you use an tripod? Which light source did you use? Which distance did you test? And on what camera model did you test the FA* ? Take a look at my thread: FA* 300mm 2.8 ED IF - thread collection - everything about the FA300/2.8 - PentaxForums.com

09-12-2020, 04:11 PM	#11
angerdan Pentaxian Join Date: Feb 2015 Photos: Gallery \| Albums Posts: 2,643	Originally posted by Mikkel128 So here one year later. I still do not get the images that I want from this lens. It may be an issue with the lens or my skills as a photographer. I hope it is the later, because it will likely be cheaper to correct. I took the lens out the other day. Attached is a sample picture. I have included som close ups to highlight the issues I am having. If anyone have any suggestions I would love to hear them! What do you guys think? Am I being too picky or is there an issue with my lens? How's the image quality with static scenes and CDAF (LiveView) ? Which AF point did you use? Is the rear filter in place?

09-23-2020, 04:21 PM	#13
clackers Otis Memorial Pentaxian Join Date: Jul 2013 Location: Melbourne Photos: Albums Posts: 16,397	Throw away that UV filter, Mikkel. It serves no protective purpose that a lens cap doesn't do better, and it can only ever degrade, not improve, the image quality you've paid for! I hope your picture was used as evidence that a millimetre of the batsman's right foot is behind the line, should be not out. (I'm a cricketer myself)