Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
09-06-2019, 11:54 AM   #1
Junior Member




Join Date: Jul 2017
Posts: 35
Sears 28mm f2.8 from the 60s

Would anyone know the procedure to adjust the infinity stop on this lens ? Will not quite reach infinity with my K50 Thanks...

Attached Images
View Picture EXIF
PENTAX K-50  Photo 
View Picture EXIF
PENTAX K-50  Photo 

Last edited by cg-4k50; 09-06-2019 at 12:00 PM.
09-06-2019, 12:39 PM   #2
Site Supporter
Site Supporter
FozzFoster's Avatar

Join Date: Jan 2016
Location: Alberta
Posts: 4,117
I'm not 100% sure, but this lens looks different the ones I've seen before - I think.
Are you sure it's m42 and not m39? Do the threads fit very well on a m42 camera?
Maybe the register distance is different for m39 lenses?
I'm honestly just spit ballin' and idea here...
09-06-2019, 12:50 PM - 1 Like   #3
Junior Member




Join Date: Jul 2017
Posts: 35
Original Poster
QuoteOriginally posted by FozzFoster Quote
I'm not 100% sure, but this lens looks different the ones I've seen before - I think.
Are you sure it's m42 and not m39? Do the threads fit very well on a m42 camera?
Maybe the register distance is different for m39 lenses?
I'm honestly just spit ballin' and idea here...
I bought the M42 adapter for my K50 and its a good fit. I also bought the 135mm f3.5 that was with this kit to the old Sears film camera that also did not reach infinity with my K50 but found directions on how, this lens is different however.
09-06-2019, 12:57 PM   #4
Pentaxian
paulh's Avatar

Join Date: Sep 2010
Location: DFW Texas/Ventura County, CA
Photos: Gallery | Albums
Posts: 19,541
Did you get the OEM type Pentax adapter or the flange-style adapter? The flange type does not allow infinity focus.

09-06-2019, 01:03 PM   #5
Otis Memorial Pentaxian
Loyal Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 33,944
QuoteOriginally posted by cg-4k50 Quote
I bought the M42 adapter for my K50 and its a good fit. I also bought the 135mm f3.5 that was with this kit to the old Sears film camera that also did not reach infinity with my K50
Two lenses and neither will attain infinity focus? I would put the blame on the adapter. Do you have a photo of it? A proper adapter will allow the lens to take its flange registration from the camera's mount face. If the lens rear flange does not contact the camera side of the mount, the adapter is at least partly and probably totally to blame. FWIW, your lens is probably 1970s vintage. Late 1960s or early 1970s.

Edit: I am reviewing previous posts regarding these two lenses. At one point, the OP was thinking they needed a T-adapter for the 135mm. It may also be that the failure to attain infinity focus applies to astrophotography. If so, very few manual focus primes at either 28mm or 135mm will have been calibrated to provide fine focus beyond relative close distances (less than half a kilometer).


Steve

Last edited by stevebrot; 09-06-2019 at 01:18 PM.
09-06-2019, 01:18 PM   #6
Junior Member




Join Date: Jul 2017
Posts: 35
Original Poster
QuoteOriginally posted by stevebrot Quote
Two lenses and neither will attain infinity focus? I would put the blame on the adapter. Do you have a photo of it? A proper adapter will allow the lens to take its flange registration from the camera's mount face. If the lens rear flange does not contact the camera side of the mount, the adapter is at least partly and probably totally to blame. FWIW, your lens is probably 1970s vintage.

Edit: I am reviewing previous posts regarding these two lenses. At one point, the OP was thinking they needed a T-adapter. It may also be that the failure to attain infinity focus applies to astrophotography. If so, very few manual focus primes at either 28mm or 135mm will have been calibrated to provide fine focus beyond relative close distances (less than half a kilometer).


Steve
I'm sure I have the correct adapter, no flange,lens screws tight to camera mount face. Here is a pic set to infinity, does it look in focus ? The tree just above the roof peak is about 100+ feet away but looks out of focus. I know not the best photo to check focus.
Attached Images
View Picture EXIF
PENTAX K-50  Photo 

Last edited by cg-4k50; 09-06-2019 at 01:32 PM.
09-06-2019, 01:35 PM - 1 Like   #7
Otis Memorial Pentaxian
Loyal Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 33,944
QuoteOriginally posted by cg-4k50 Quote
I'm sure I have the correct adapter, no flange,lens screws tight to camera mount face. Here is a pic set to infinity, does it look in focus ?
At Web resolution...yes, it appears to be in focus for all elements in the frame. That being said, it would not surprise me if the lens were calibrated such that the plane of focus at the infinity stop might be as close as 55 meters distant and perhaps even closer.* You may be able to adjust to a further distance appropriate for astro, but I can provide no guidance for that task. Be aware that 28mm lenses of that vintage often have a fair amount of field curvature such that the the corners and edges may not attain the same quality focus as the center.


Steve

* This is not unreasonable given the DOF at commonly used apertures, the capabilities of the viewfinder focusing systems without supplemental magnification, even with a split image, and the mechanical limitations of the focus mechanism. I just checked an early 1970s Kipon-made Vivitar 28/2.5 and it is calibrated to about 30 meters at the infinity stop.

Last edited by stevebrot; 09-06-2019 at 01:49 PM.
09-06-2019, 01:36 PM   #8
Junior Member




Join Date: Jul 2017
Posts: 35
Original Poster
QuoteOriginally posted by paulh Quote
Did you get the OEM type Pentax adapter or the flange-style adapter? The flange type does not allow infinity focus.
Yes the adapter inserts flush to the camera mount face...

09-06-2019, 04:48 PM - 1 Like   #9
Junior Member




Join Date: Jul 2017
Posts: 35
Original Poster
Was able to adjust and now can go past infinity all is good. First pic at infinity before adjustment, distance about 200'
Attached Images
View Picture EXIF
PENTAX K-50  Photo 
View Picture EXIF
PENTAX K-50  Photo 
09-06-2019, 10:57 PM - 1 Like   #10
Pentaxian
ZombieArmy's Avatar

Join Date: Jun 2014
Location: Florida
Posts: 1,878
A lot of older manual lenses aren't calibrated for proper infinity because you couldn't really tell on film when stopped down anyways. I've got quite a few I need to adjust myself.
09-07-2019, 07:43 AM - 1 Like   #11
Pentaxian
Ontarian50's Avatar

Join Date: Mar 2015
Posts: 452
QuoteOriginally posted by ZombieArmy Quote
A lot of older manual lenses aren't calibrated for proper infinity because you couldn't really tell on film when stopped down anyways. I've got quite a few I need to adjust myself.
Oh, you can tell.

However, I do agree that many older lenses aren't properly calibrated. A lot of third party lenses, like the Sears one in this thread, likely didn't get exact calibration and quality control on their way down the assembly line. And it's true that if the average punter who bought budget optics took all vacation snaps at F8 or F11, they might never notice it didn't quite reach infinity.

But given that most old lenses of this type use a friction ring to clamp the focus ring onto the helical, a small slip here and there over time results in a lens that either goes well past infinity, or comes up short.

A top grade Takumar or Nikkor should have been spot on when it left the factory. But time, cold and hot weather, sticky greases (although Takumars pretty much never get sticky), can mess up that precise calibration.
09-07-2019, 08:14 AM   #12
Junior Member




Join Date: Jul 2017
Posts: 35
Original Poster
QuoteOriginally posted by stevebrot Quote
At Web resolution...yes, it appears to be in focus for all elements in the frame. That being said, it would not surprise me if the lens were calibrated such that the plane of focus at the infinity stop might be as close as 55 meters distant and perhaps even closer.* You may be able to adjust to a further distance appropriate for astro, but I can provide no guidance for that task. Be aware that 28mm lenses of that vintage often have a fair amount of field curvature such that the the corners and edges may not attain the same quality focus as the center.


Steve

* This is not unreasonable given the DOF at commonly used apertures, the capabilities of the viewfinder focusing systems without supplemental magnification, even with a split image, and the mechanical limitations of the focus mechanism. I just checked an early 1970s Kipon-made Vivitar 28/2.5 and it is calibrated to about 30 meters at the infinity stop.
Well was able to focus on the MW last night and like you said not a great lens for AP. Don't need to look far from the center of image to see the field curvature. Stopped down to F8, F4 was vary bad. Two min exposure ISO 800 bortle 8 sky.
Attached Images
 

Last edited by cg-4k50; 09-07-2019 at 08:23 AM.
09-07-2019, 03:57 PM   #13
Otis Memorial Pentaxian
Loyal Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 33,944
QuoteOriginally posted by Ontarian50 Quote
However, I do agree that many older lenses aren't properly calibrated.
Define properly calibrated.* Limitations regarding infinity stop are common to every prime lens on my shelf save two, my DA 50/1.8 and Sigma EX DG 50/2.8 Macro. None of the others (my recent FA 77/1.8 Limited and FA 35/2.0 included) can attain focus past about 2000X the focal length distance.** Based on an article I read several years ago (have not been able to find it since) detailing the industry conventions regarding infinity calibration, I believe this is intentional and that my lenses have not "drifted close" with age.


Steve

* I should have put a smiley there because there are differences between practical (based on CoC), desirable (the stars), and absolute (optical bench at arbitrary precision) with desirable being the most difficult to satisfy.

** Pentax K-3, magnified live view, 21 C at maximum aperture confirmed with actual exposure.
09-07-2019, 07:33 PM - 1 Like   #14
Pentaxian
ZombieArmy's Avatar

Join Date: Jun 2014
Location: Florida
Posts: 1,878
QuoteOriginally posted by stevebrot Quote
I believe this is intentional and that my lenses have not "drifted close" with age.
I'd say this is generally true but it's not hard to tell when a lens is out of spec. For example my A50 1.4 simply won't focus past about 20 feet and needs repair.

Personally I've just come to like lenses that focus past infinity, makes my life easier.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
infinity, k-mount, pentax lens, sears 28mm f2.8, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Any good wide angle lenses from 60s/70s? torontoem4o Pentax SLR Lens Discussion 24 06-30-2014 07:08 PM
Machinery Meat and Spuds of the '60s and '70s . . . . . . Sailor Post Your Photos! 17 06-21-2014 02:58 PM
For Sale - Sold: Pentax A 28mm f2.8 ; Inexpensive Sears KSX & Prospec 28-70 & Sears 50mm f2 & Filters stillnk Sold Items 4 11-15-2012 03:43 PM
Why not make a Pentax DSLR in the shape of old Spotmatics and 60s/70s film cameras? PentaxForums-User Pentax DSLR Discussion 40 03-18-2011 12:30 AM
A Catalog From The Late 60s konraDarnok Pentax Film SLR Discussion 29 01-26-2009 09:14 PM



All times are GMT -7. The time now is 05:42 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top