Pentax-A 35-105 mm

Greenleaf · 05-26-2023, 01:29 AM

Hi Everyone,

I have a focusing issue using this lens with adapters. On a Fujifilm X-T2 and X-E1 with two different PK to FX adapters, focusing has switched from parafocal to verifocal. Focusing no longer remains fixed when zooming. I also tried it an an old Zenit analogue camera and it remains in focus at any focal length so the lens is not the problem. Has anyone experienced this using adapters and found a solution? Anyone know why this is the case?
Have a great day!

Robot camera · 05-26-2023, 02:20 AM

It might be that it's much easier to detect slight focus shift on the Fuji cameras. Also, a degree of focus shift that wouldn't be noticed on a print from a 35mm film camera (typically no more than a 10 or 12 inch long print) might be very obvious in an image at high magnification on the computer. I've always refocused after zooming, film or digital; I think I read somewhere years ago that no zoom lens is truly parafocal.

**UncleVanya** · 05-26-2023, 06:01 AM

One more potential issue is that adapters are often slightly too short on purpose. The shorter than optimal distance negatively impacts edges on wide angle lenses. Perhaps it also distorted the parfocal nature of the lens? NovaFlex makes excellent adapters (pricey) that seem to have accurate mounting distances.

**JoelA** · 05-26-2023, 06:04 AM

My copy of the this lens (sn# 5281241) does not maintain focus when zooming either on full frame or crop digital (K-1II and K-50) or film cameras (K2 and Ricoh XR-2s).

**UncleVanya** · 05-26-2023, 07:21 AM

Originally posted by JoelA

My copy of the this lens (sn# 5281241) does not maintain focus when zooming either on full frame or crop digital (K-1II and K-50) or film cameras (K2 and Ricoh XR-2s).

Ah. Then the lens must not be parfocal after all.

AfterPentax Mark II · 05-26-2023, 08:26 AM

Originally posted by UncleVanya

Ah. Then the lens must not be parfocal after all.

Or that lens has an issue. I own the A 35-105 from when it was issued and it still parfocal all the way. (The real) Pentax always indicated that the best result is starting at 105 and go back to 35 to prevent minor distortions. It is what modern camera's can do today with LV, magnify for manual focusing.

**StiffLegged** · 05-27-2023, 12:44 AM

I use mine on a K7 without focusing issues, using the green indicator in the viewfinder, and generally at the focal length I’m about to use. Can’t say what problem you might have with the Fujis, but are you using the manual focussing aids they have? Comparisons with a film-era Zenit are not really useful, APS-C digital is appreciably higher resolution than film.

It’s my most used lens and a fine one at that.

**JoelA** · 05-27-2023, 04:42 AM

Ugh. Mine is definitely a stinker. I bought it well used a few years ago. A couple times I thought I was losing my mind as what seemed in focus in the viewfinder was not in focus on the shot. Took out a tripod and did a side by side test with a few equal focal length primes. There's definitely some focus issues and even they are not consistent. Looks like I now have a pretty paperweight!

05-26-2023, 01:29 AM	#1
Greenleaf New Member Join Date: May 2023 Posts: 1	Pentax-A 35-105 mm Hi Everyone, I have a focusing issue using this lens with adapters. On a Fujifilm X-T2 and X-E1 with two different PK to FX adapters, focusing has switched from parafocal to verifocal. Focusing no longer remains fixed when zooming. I also tried it an an old Zenit analogue camera and it remains in focus at any focal length so the lens is not the problem. Has anyone experienced this using adapters and found a solution? Anyone know why this is the case? Have a great day!

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05-26-2023, 02:20 AM	#2
Robot camera Senior Member Join Date: Mar 2013 Location: Milton Keynes, Buckinghamshire Posts: 194	It might be that it's much easier to detect slight focus shift on the Fuji cameras. Also, a degree of focus shift that wouldn't be noticed on a print from a 35mm film camera (typically no more than a 10 or 12 inch long print) might be very obvious in an image at high magnification on the computer. I've always refocused after zooming, film or digital; I think I read somewhere years ago that no zoom lens is truly parafocal.

05-26-2023, 06:01 AM	#3
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,460	One more potential issue is that adapters are often slightly too short on purpose. The shorter than optimal distance negatively impacts edges on wide angle lenses. Perhaps it also distorted the parfocal nature of the lens? NovaFlex makes excellent adapters (pricey) that seem to have accurate mounting distances.

05-26-2023, 06:04 AM	#4
JoelA Loyal Site Supporter Join Date: Feb 2019 Location: Florida Photos: Gallery Posts: 187	My copy of the this lens (sn# 5281241) does not maintain focus when zooming either on full frame or crop digital (K-1II and K-50) or film cameras (K2 and Ricoh XR-2s).

05-26-2023, 07:21 AM	#5
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,460	Originally posted by JoelA My copy of the this lens (sn# 5281241) does not maintain focus when zooming either on full frame or crop digital (K-1II and K-50) or film cameras (K2 and Ricoh XR-2s). Ah. Then the lens must not be parfocal after all.

05-26-2023, 08:26 AM	#6
AfterPentax Mark II Pentaxian Join Date: Mar 2021 Posts: 1,467	Originally posted by UncleVanya Ah. Then the lens must not be parfocal after all. Or that lens has an issue. I own the A 35-105 from when it was issued and it still parfocal all the way. (The real) Pentax always indicated that the best result is starting at 105 and go back to 35 to prevent minor distortions. It is what modern camera's can do today with LV, magnify for manual focusing.

05-27-2023, 12:44 AM	#7
StiffLegged Site Supporter Join Date: Jan 2018 Photos: Gallery Posts: 4,635	I use mine on a K7 without focusing issues, using the green indicator in the viewfinder, and generally at the focal length I’m about to use. Can’t say what problem you might have with the Fujis, but are you using the manual focussing aids they have? Comparisons with a film-era Zenit are not really useful, APS-C digital is appreciably higher resolution than film. It’s my most used lens and a fine one at that.

05-27-2023, 04:42 AM	#8
JoelA Loyal Site Supporter Join Date: Feb 2019 Location: Florida Photos: Gallery Posts: 187	Ugh. Mine is definitely a stinker. I bought it well used a few years ago. A couple times I thought I was losing my mind as what seemed in focus in the viewfinder was not in focus on the shot. Took out a tripod and did a side by side test with a few equal focal length primes. There's definitely some focus issues and even they are not consistent. Looks like I now have a pretty paperweight!