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Thread: How to get a scope to focus at 10 metres.

  1. #16
    Join Date
    Nov 2001
    Location
    Blackburn, Lancs. (under a bridge)
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    20,320
    Quote Originally Posted by thisisdonald View Post
    In the past I have used a pair of straight engineers calipers to unwind lens carriers. I used the kind that have a threaded rod between the legs.
    Ive used a vernier gauge before now. It depends on how tight the collar is.

  2. #17
    Join Date
    Sep 2012
    Location
    Paisley, Renfrewshire, Scotland.
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    4,203
    Quote Originally Posted by I. J. View Post
    Ive used a vernier gauge before now. It depends on how tight the collar is.
    Definitely. I got beat with a Hawke Panorama. I think they used gorilla glue!
    Donald

  3. #18
    Join Date
    Mar 2010
    Location
    Rossendale and Formby
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    4,491
    Quote Originally Posted by RobinC View Post
    Hi Bob

    I shot ten metre running boar (Running rat) quite seriously many years back, Now PC incorrect, and now just moving target, we had the same problem getting scopes generally set for 100 mts correct at 10 mts.

    Don't mess about trying to adjust the lens its a real hassle, what we did was go to a local lens maker/optician, you need a +0.1 dioptre lens added to the front, the tolerance on plain lenses is 0.1 of a dioptre, which is what you need, if you have a friendly one he will sort and test his plain lenses until he finds one on 0.1.
    Get it ground to the correct diameter, then pop out the front ring put an "o" ring either side of the lens and pop the ring back. Voile, corrected to ten metres, and easy to take out to return scope to standard.

    Have Fun
    Robin
    That’s another good idea - and one that you have used with 10 metres competition shooting - so it obviously works well.

    I also like the idea of being able to keep the one lens that could possibly be used in other scopes of the same size - but at around £15 for a lens ( assuming a similar price as a shooting spectacle lens) that may not be as important as being able to return the scope to original spec just by removing the “O” rings.

    I have a couple of non AO scopes that are probably not worth much these days, so I can experiment with them and see what works best.

    A scope with a really solid front lens holder may not adjust so a “drop-in” additional correction lens would cover that sinario too!
    Rossendale Model Target Club every Tuesday and Thursday evening 7 - 10pm.

  4. #19
    Join Date
    Sep 2010
    Location
    Belper
    Posts
    394
    Hi Bob,
    one option I've used applies to older small tube scopes eg. 4 x 20 Nikko Sterlings or old 3/4" tubed Weavers. With these the objective lens is fitted into a separate section and threaded onto the main tube. A bit of trial and error with fitting an "o" ring or suitable washer on the threaded portion will give a closer focus and is easily reversible.
    The only drawback is these smaller scopes are not the best for indoor use, but some are useable.

    Cheers
    torrens

  5. #20
    Join Date
    Jul 2015
    Location
    Hastings
    Posts
    863
    Bob,

    A cheap & cheerful method :

    Set the focus of the scope to its minimum value, then cover the objective lens with a piece of aluminium foil, and poke a small hole in the foil.

    Start with a very small diameter hole, then work upwards - it is a compromise between a brighter image and maximum depth of focus - just like any aperture.

    The hole in the foil does not need to be in the centre of the field.

    This technique of using a sub-aperture mask has been used quite a lot with astronomical telescopes.

    Have fun & a good weekend

    Best regards

    Russ

  6. #21
    Join Date
    Mar 2010
    Location
    Rossendale and Formby
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    4,491
    Quote Originally Posted by PhatMan View Post
    Bob,

    A cheap & cheerful method :

    Set the focus of the scope to its minimum value, then cover the objective lens with a piece of aluminium foil, and poke a small hole in the foil.

    Start with a very small diameter hole, then work upwards - it is a compromise between a brighter image and maximum depth of focus - just like any aperture.

    The hole in the foil does not need to be in the centre of the field.

    This technique of using a sub-aperture mask has been used quite a lot with astronomical telescopes.

    Have fun & a good weekend

    Best regards

    Russ
    How about that?

    Heath Robinson and applied science - I like it!

    Enjoy your weekend,

    Bob.
    Rossendale Model Target Club every Tuesday and Thursday evening 7 - 10pm.

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