Checking and adjusting PU scope focus
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Thread: Checking and adjusting PU scope focus

  1. #1
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    Default Checking and adjusting PU scope focus

    I added 2 new Mosin PUs to the three I already had recently. I usually take these 2 at a time to the range and I started to notice some differences. The sight picture (@100 yds.) in one of the newer PUs was sharper and clearer than my original 3 and the other was not nearly as good. I had previously observed that I could see better through 2 of my older scopes with corrective lenses but the third one I used just plain safety glasses because my prescription glasses made the image less sharp.

    No knowing any better, I always assumed that the less than perfect focus was the state of the art at the time.

    I did an experiment at the range yesterday. I slowly unscrewed the eye piece on on one of the less clear scopes and the target came into very sharp focus after about 4 turns. Unscrewing the eyepiece changes the relationship between the eyepiece and the central lens block. Those who have disassembled these scopes know that the central lens block is adjustable and held in place by one or two (depends on the year/maker) very small set screws.You could make adjustments at the range but it is better to do this in a clean area where you have half a chance of finding the lock screws if you drop them.

    I set up my rifles in a cleaning fixture (in the basement) and posted the target shown below at a distance of 11 meters (35 feet). If you wear corrective lenses when you are shooting, make sure you wear them to do this test. The smallest dot is is 0.75 mm and the next larger one is 1.5 mm. If your scope is focused properly you should be able to clearly make out the 1.5 mm circle and just see the 0.75 mm dot (red circled).

    If they aren't clear, slowly unscrew the eyepiece until the come into sharp focus. To make the fix permanent you must adjust the central lens block. Do this one turn at a time and fully screw in the eyepiece to check after each adjustment. This can be a little tedious but it will be worth it. Once you have the assembly in sharp focus, reinstall the locking screws and reseal the eyepiece lens assembly with optical grease. (See the sticky on how to disassemble and clean a PU scope).

    Click image for larger version. 

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  2. #2
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    Solid information, thank you for sharing!

  3. #3
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    It sounds like the older glue used on lenses may have shrunk a bit changing focus - postwar refurbs all got new coated lenses and new modern glue as well as a reblue and polish, often at the Kiev Arsenal Optics Plant.

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  5. #4
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    Interesting post. I simply take about 5 cheap reading glasses to the range to compensate. I get them for $1 each.

    Originally, these were set for good eyes or properly corrected ones. I have also tried moving/unscrewing the objective lens to make the picture more clear. It does help but it may makes the Reticule less clear so a trade off.

  6. #5
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    Quote Originally Posted by mike radford View Post
    Interesting post. I simply take about 5 cheap reading glasses to the range to compensate. I get them for $1 each.

    Originally, these were set for good eyes or properly corrected ones. I have also tried moving/unscrewing the objective lens to make the picture more clear. It does help but it may makes the Reticule less clear so a trade off.
    That is what I found until you use your prescription glasses. The is a point in adjusting the central lens block where both the target and the reticle are clear and sharp. Properly adjusted, these scopes are as clear and sharp as good quality modern examples; not Schmitt and Bender but as good as $500-700 scopes.

    I agree that the factory original setting was probably for people with excellent uncorrected vision. Not much call for fifty something, near-sighted recruits as snipers.

  7. #6
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    Great post.

    I will try with reading glasses see how it plays out. just like you I use shooting glass or cheap plastic ones. I am near sighted so the lens seems clear for me. Nothing wrong with trying new methods. IMO This may help with iron sights as well.....

    unfortunately, with my one other zf4 reading glasses may not help lol

  8. #7
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    Quote Originally Posted by mike radford View Post

    .... I have also tried moving/unscrewing the objective lens to make the picture more clear. It does help but it may makes the Reticule less clear so a trade off.
    Moving the objective (front) lens will affect parallax setting and can destroy accuracy due to parallax being way off.

    Daniel39

  9. #8
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    any reason why the rear could not be loctite'd at the new location and not mess with the internals ??

  10. #9
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    Quote Originally Posted by ar10ar15man View Post
    any reason why the rear could not be loctite'd at the new location and not mess with the internals ??
    I suppose you could but "messing with the internals" would be easier and less intrusive as far as the original design is concerned.

    Probably the biggest problem you will encounter is loosening the rear lens assembly - these can be very tight and difficult to remove without damaging the scope tube or finish. If you get this loose, the lock screws are easy to remove and a pair of mini needle nose pliers will fit in the lens block assembly to allow adjustment. If you have lots of scopes to adjust, I will post a $2 tool you can make adjust the lens block (not worth the effort is you just have one or two).

    Early SVT type scopes (my 2 examples at least) with the larger diameter tube that houses the ocular lenses use an internal "jam screw" in addition to one external lock screw. It isn't necessary to remove this screw completely; just loosen it 3-4 turns so the lens block can be screwed without much force. Do not over-tighten this screw when you re-install it.

    Tips for loosening the rear lens assembly:

    1. You won't find anything better than the scope mount to counter the turning forces needed to remove the lens. Leave the scope in the mount and clamp the mount securely into a padded vise.

    2.Try loosening the assembly by hand with a rubber glove for grip. Next try a strap wrench. You can make a very effective wrench by cutting a 1.25" hole in 3/4 plywood and then ripping through the hole. Wrap the lens in heavy rubber or layers of tape. Use a series of bar clamps along the rip line to gradually increase the grip force while turning. Don't forget to consider "leaving well enough alone" if you find yourself applying a lot of force. So far I have been successful but eventually enough force will cause the threads to separate ruining both the lens assembly and the tube. Be extra careful if the lens block is a white metal alloy - some of these alloys weaken significantly with age.

    3. Don't use heat to attempt to loosen the lens block. The composite lens is secured with balsam which will yellow, crack or fail completely if over heated. Don't use penetrating oils or solvents. These might damage the lenses or, at the very least, will require you to fully dis-assemble the scope for cleaning.

    Below is a successful improvised wrench:

    Click image for larger version. 

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  11. #10
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    Quote Originally Posted by marc_j View Post
    Properly adjusted, these scopes are as clear and sharp as good quality modern examples; not Schmitt and Bender but as good as $500-700 scopes.
    Not to hijack the thread but I must say that the optical quality of Soviet scopes is quite astonishing. I do not have a PU-scope but I must say that my 1937 Progress made PE scope has unbelievably clear and sharp image. The glass used on lenses is really high quality and the optical quality of the image can compete with modern scopes surprisingly well.

  12. #11
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    Quote Originally Posted by Bugelson View Post
    Not to hijack the thread but I must say that the optical quality of Soviet scopes is quite astonishing. I do not have a PU-scope but I must say that my 1937 Progress made PE scope has unbelievably clear and sharp image. The glass used on lenses is really high quality and the optical quality of the image can compete with modern scopes surprisingly well.
    I could not agree more. I have original PE and PEM scopes and the optics is very impressive. A couple are beat to heck and they still have impressive optics. I have seen dug scopes that are clear. Some PUs will show a bullet hole at 100 yds. Try that with many period scopes. They did a good job on these scopes IMO.

  13. #12
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    Quote Originally Posted by mike radford View Post
    I could not agree more. I have original PE and PEM scopes and the optics is very impressive. A couple are beat to heck and they still have impressive optics. I have seen dug scopes that are clear. Some PUs will show a bullet hole at 100 yds. Try that with many period scopes. They did a good job on these scopes IMO.
    This is why I started trying to improve the focus on my PUs and why I started this thread. With one scope I could see bullet holes in white paper at 100 yds., but the others I could not. Correcting the focus allows me to see bullet holes at 100 yds with all my PU scopes.

  14. #13
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    Is it basically the same procedure to focus a PEM scope? I have a PEM that is just ever so slightly out of focus and it would be great if I could sharpen it up.

    Thanks...

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    Quote Originally Posted by Bugelson View Post
    Not to hijack the thread but I must say that the optical quality of Soviet scopes is quite astonishing. I do not have a PU-scope but I must say that my 1937 Progress made PE scope has unbelievably clear and sharp image. The glass used on lenses is really high quality and the optical quality of the image can compete with modern scopes surprisingly well.
    This carries over to later Soviet optics too, I have an early '70s PSO-1 scope on my SVD and I gave the rifle to someone at the range to try and the first thing they said was the scope was as clear as their 2.5K Schmidt and Bender!.They were even more gobsmacked when I told them how much I paid for it!.
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  16. #15
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    I just adjusted a PU the other day...recent aquisition...I did so by removing the eyepiece and adjusting the inner center lens..a little trial and error and it is excellent. Was rather easy actually.

  17. #16
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    So I was tinkering with my slightly out of focus PE scope today and I was able to remove the tiny screw that holds the rear lens housing in place and I unscrewed the housing 2-3 turns and the focus sharpened right up. I know PU scopes can be focused pretty easily looking at the Sticky post regarding PU disassembly by removing the small external screw and adjusting the central lens block. Does anyone know if the same can be done with a PE scope? Do they also have an adjustable central lens block?

    Thanks

  18. #17
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    I suspect they are similar....I have a Pe and PEM...I believe you are talking about a PEM as the PE has an adjustable reticle that was deleted on the PEM scope.
    I've seen a few sites where they mislabel.
    I believe the PE stood for 'Unified Model' and had the adjustable eye reticle.
    The PEM stood for 'Unified Model Modern' and had no adjustable eye reticle.

    Remove the rear eyepiece then and see...or talk/pm Ratnik or Raspootyn about that adjustment.....I've done PU's by adjusting the center lens but never a PEM.

  19. #18
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    My bad... I am talking about a PEM scope.

  20. #19
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    No sweat...just wanted to make sure we were on the same sheet of music. If you have loosened the rear sight piece than I'd take a gander and see what's what.
    I'd do serious search to see if you can find any tutorial and pm Ratnik and Raspootyn too.....
    Are you talking an original or a Ukrainian later model made as an original.....show us a pic....nice to see them anyways....my PEM looks almost new...Click image for larger version. 

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ID:	3659561..and the optics are excellent. 1937

    Marcj….I'd not Loctite the rear eyepiece in any stand off position....if I was going that route I'd make/find an appropriate sized spacer ring/shim like a copper ring washer used for sealing engine sump bolts etc...
    Adjusting the inner lens sounds harder than it is...took a few minutes only with moving it.... reassembly.... and the eyeball test and just do that until satisfied...really made a huge dif. Either way take your time and be precise...keep the innards clean of particulate matter.

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