AF not working around infinity with FA* 300mm f4 and 645Z

gfje · 10-03-2018, 01:59 AM

Hello out there,

I am a relatively new member based in Germany and am using the 645Z only for a short time now.

I have bought a used pentax-FA* 645 300mm F4 ED [IF]. The lens looks really great. The seller, who is not the ex-owner, has sent the lens with an invoice for a check and a calibration ordered by the previous owner (not the seller). I noticed that the AF is struggling when trying to focus to infinity. Subjects in close or medium distance are focused correctly. When focussing to infinty the camera overrides the inifity mark and then struggles to go in the oposite direction. It seems like the AF is stuck. This only occurs with the 300mm lens. With all my other lenses the AF is working perfectly. So I assume it's an issue of the lens. In manual mode it works just fine. The focussing is really smooth.

Has anybody had similar experiances or is this a common/known issue? I personally doubt this. The AF should work fine no matter how far the subject is away.

Many thanks in advance, Guido

victormeldrew · 10-03-2018, 02:45 AM

It is possible that the previous owner had the lens calibrated to fix an infinity issue with their body, that has left it beyond the range of your body.

gfje · 10-03-2018, 05:40 AM

Originally posted by victormeldrew

It is possible that the previous owner had the lens calibrated to fix an infinity issue with their body, that has left it beyond the range of your body.

maybe, but i have some doubts because there is no camera mentioned on the invoice just the lens itself and a 1.4 TC

Bob L · 10-03-2018, 07:59 AM

Is it possible that it was recalibrated to allow the use of AF during infrared shooting?

**ProfessorBuzz** · 10-03-2018, 08:20 AM

Have you tried adjusting the AF fine tuning menu item to see if it behave differently?

Adam · 10-03-2018, 08:53 AM

Have you performed a FF/BF test and adjusted accordingly via the camera's AF fine tune menu? If not, go ahead and do so as it may help. Calibrations vary by both the lens and camera, so even if the lens worked perfectly with another camera, it may need adjustments on yours.

Bob L · 10-03-2018, 09:10 AM

Originally posted by Adam

Have you performed a FF/BF test and adjusted accordingly via the camera's AF fine tune menu? If not, go ahead and do so as it may help. Calibrations vary by both the lens and camera, so even if the lens worked perfectly with another camera, it may need adjustments on yours.

If "subjects in close or medium distance are focused correctly" then AF fine tune is not a likely candidate is it?

Adam · 10-03-2018, 09:33 AM - **1 Like**

Originally posted by Bob L

If "subjects in close or medium distance are focused correctly" then AF fine tune is not a likely candidate is it?

Sounds like this is a subjective evaluation, so I'd still perform the test. It may only take a very small adjustment to get AF to lock at infinity.

gfje · 10-03-2018, 09:31 PM

Originally posted by ProfessorBuzz

Have you tried adjusting the AF fine tuning menu item to see if it behave differently?

Thank you for the hint. I didn't know about this function and wil try it later.

gfje · 10-03-2018, 09:34 PM

Originally posted by Adam

Have you performed a FF/BF test and adjusted accordingly via the camera's AF fine tune menu? If not, go ahead and do so as it may help. Calibrations vary by both the lens and camera, so even if the lens worked perfectly with another camera, it may need adjustments on yours.

Thank you, Adam. I will check it this evening as soon as I am back from work. Seems like I've forgotten the basics...

Adam · 10-04-2018, 11:16 AM - **1 Like**

Originally posted by gfje

Thank you, Adam. I will check it this evening as soon as I am back from work. Seems like I've forgotten the basics...

No problem! Here's a guide with info on where to adjust the settings and how to perform a controlled test:

Fixing Front and Back Focus - Introduction - In-Depth Articles

gfje · 10-05-2018, 12:49 PM

Just a quick update: I tried the focus adjustment but without success. But I am happy to have learned about this function. I really wasn't aware of it. In the meantime I had a chat with the technician who did the calibration the pre-owner had ordered. He asked me to send the lens back for another check (free of charge). And I did it today.

10-03-2018, 01:59 AM	#1
gfje New Member Join Date: May 2016 Posts: 20	*AF not working around infinity with FA 300mm f4 and 645Z** Hello out there, I am a relatively new member based in Germany and am using the 645Z only for a short time now. I have bought a used pentax-FA* 645 300mm F4 ED [IF]. The lens looks really great. The seller, who is not the ex-owner, has sent the lens with an invoice for a check and a calibration ordered by the previous owner (not the seller). I noticed that the AF is struggling when trying to focus to infinity. Subjects in close or medium distance are focused correctly. When focussing to infinty the camera overrides the inifity mark and then struggles to go in the oposite direction. It seems like the AF is stuck. This only occurs with the 300mm lens. With all my other lenses the AF is working perfectly. So I assume it's an issue of the lens. In manual mode it works just fine. The focussing is really smooth. Has anybody had similar experiances or is this a common/known issue? I personally doubt this. The AF should work fine no matter how far the subject is away. Many thanks in advance, Guido

10-03-2018, 08:53 AM	#6
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,595	Have you performed a FF/BF test and adjusted accordingly via the camera's AF fine tune menu? If not, go ahead and do so as it may help. Calibrations vary by both the lens and camera, so even if the lens worked perfectly with another camera, it may need adjustments on yours. Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

10-03-2018, 09:33 AM - 1 Like	#8
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,595	Originally posted by Bob L If "subjects in close or medium distance are focused correctly" then AF fine tune is not a likely candidate is it? Sounds like this is a subjective evaluation, so I'd still perform the test. It may only take a very small adjustment to get AF to lock at infinity. Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

10-04-2018, 11:16 AM - 1 Like	#11
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,595	Originally posted by gfje Thank you, Adam. I will check it this evening as soon as I am back from work. Seems like I've forgotten the basics... No problem! Here's a guide with info on where to adjust the settings and how to perform a controlled test: Fixing Front and Back Focus - Introduction - In-Depth Articles Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
300mm F4 A or 300mm F4 FA....??	BostonUKshooter	Pentax Medium Format	7	06-05-2018 10:52 PM
For Sale - Sold: Pentax 645 NII, 35mm f3.5 A, 45-85mm f4.5 FA, 80-160mm f4.5 FA, 300mm f5.6 FA	Kmtn	Sold Items	2	04-08-2013 09:28 AM
Looking for a cheap telezoom: Pentax-FA 100-300mm F4.7-5.8 or Tamron 70-300mm F4-5.6	Matchete	Pentax SLR Lens Discussion	30	01-05-2012 05:04 AM
Why don't all lenses have infinity exactly on the infinity stop?	peterh337	Pentax SLR Lens Discussion	19	01-15-2011 08:53 PM
FA 100-300mm f4.7-5.8 or FA 100-300mm f4.5-5.6 ?	Aloïs	Pentax SLR Lens Discussion	5	03-25-2010 01:24 PM

10-03-2018, 02:45 AM	#2
victormeldrew Veteran Member Join Date: Jun 2015 Location: South West UK Photos: Albums Posts: 1,493	It is possible that the previous owner had the lens calibrated to fix an infinity issue with their body, that has left it beyond the range of your body.

10-03-2018, 05:40 AM	#3
gfje New Member Join Date: May 2016 Posts: 20 Original Poster	Originally posted by victormeldrew It is possible that the previous owner had the lens calibrated to fix an infinity issue with their body, that has left it beyond the range of your body. maybe, but i have some doubts because there is no camera mentioned on the invoice just the lens itself and a 1.4 TC

10-03-2018, 07:59 AM	#4
Bob L Senior Member Join Date: Mar 2016 Location: La Vienne (86), France Posts: 223	Is it possible that it was recalibrated to allow the use of AF during infrared shooting?

10-03-2018, 08:20 AM	#5
ProfessorBuzz Loyal Site Supporter Join Date: Feb 2018 Posts: 1,903	Have you tried adjusting the AF fine tuning menu item to see if it behave differently?

10-03-2018, 09:10 AM	#7
Bob L Senior Member Join Date: Mar 2016 Location: La Vienne (86), France Posts: 223	Originally posted by Adam Have you performed a FF/BF test and adjusted accordingly via the camera's AF fine tune menu? If not, go ahead and do so as it may help. Calibrations vary by both the lens and camera, so even if the lens worked perfectly with another camera, it may need adjustments on yours. If "subjects in close or medium distance are focused correctly" then AF fine tune is not a likely candidate is it?

10-03-2018, 09:31 PM	#9
gfje New Member Join Date: May 2016 Posts: 20 Original Poster	Originally posted by ProfessorBuzz Have you tried adjusting the AF fine tuning menu item to see if it behave differently? Thank you for the hint. I didn't know about this function and wil try it later.

10-03-2018, 09:34 PM	#10
gfje New Member Join Date: May 2016 Posts: 20 Original Poster	Originally posted by Adam Have you performed a FF/BF test and adjusted accordingly via the camera's AF fine tune menu? If not, go ahead and do so as it may help. Calibrations vary by both the lens and camera, so even if the lens worked perfectly with another camera, it may need adjustments on yours. Thank you, Adam. I will check it this evening as soon as I am back from work. Seems like I've forgotten the basics...

10-05-2018, 12:49 PM	#12
gfje New Member Join Date: May 2016 Posts: 20 Original Poster	Just a quick update: I tried the focus adjustment but without success. But I am happy to have learned about this function. I really wasn't aware of it. In the meantime I had a chat with the technician who did the calibration the pre-owner had ordered. He asked me to send the lens back for another check (free of charge). And I did it today.