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Thread: Objective Lens Size

  1. #1
    Sharp Shooter

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    Default Objective Lens Size

    What is the pro's and cons for having big and small objective lenses? I especially want to know the advantages a smaller objective lens will give you. I am thinking of this especially that we are now starting HFT.
    What will the difference be for scopes used in FT and HFT?

  2. #2
    Inactive Member

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    AFIK, The bigger objective lets in more light, so it's easier to shoot with in low light conditions.

  3. #3
    Inactive Member

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    FT the scope is used for range finding, and HFT you need to use the scope for all the targets 8-45 yds? on one setting.

    smaller objective = deeper field of view.....

    in the UK, 10X "sniper" scopes are very popular for HFT. and imho some sort of multi aim point (md/map/sr/nato...etc)reticle is ideal

  4. #4
    Sharp Shooter

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    The new scope from Hawk will be great for HFT. When they will be available here is another story.

  5. #5
    Marksman
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    pros of small objective lenses...none except maybe a weight [and money] saving

  6. #6
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    was looking through my scope with 60mm lense compared to my brothers 44mm and you can definitly seen the difference in light transmission when it starts to get dark in the evening.

  7. #7
    Sharp Shooter
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    Arnold , why the face mask?

  8. #8
    Sharp Shooter

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    I was suppose to use it for dust, but my glasses fogged up so I ended up not using it.

    Urabus I have also read about this deeper field of view on smaller objective lenses. Does this mean the picture stays in focus for a longer range?

    So for HFT you use small objective and FT as big as you can go?

  9. #9
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    >> I was suppose to use it for dust, but my glasses fogged up so I ended up not using it.
    Interesting thing I noticed though. Without my glasses, The image through scope is a lot more focused. If I use my glasses everything is very blurred. Strange...

  10. #10
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    Too many lenses. Same here. :O
    AFA low light shooting is concerned. We normally shoot in good light when shooting FT or HFT, except if you shoot Jason's night range. 8) The depth of the picture makes no diffs for me as I shoot on 10x only. I only use the big mag. for range finding.

  11. #11
    Sharp Shooter
    The Professor

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    One thing to consider in relation to lens size against brightness is the exit pupil of the scope i.e the diameter of the beam of light that comes through the eyepiece. to establish this divide your objective lens size (mm) by the magnification e.g. for a 6x42: 42/6 = 7mm

    Now relate this to the size of the pupil in the eye, so IIRC maximum normal dilation of the pupil is around 7mm in low light conditions. So a 6x scope with a 56mm lens is not going to give you a brighter image as your eye is unable to use the extra light. What the larger lens allows is the magnification to be increased to 8x and still gives maximum usable light.

    In relation to HFT the smaller lens size will give a slightly greater depth of focus, given in the UK HFT rule no scope twiddling is allowed there is a benefit to this. In FT however the smallest possible depth of focus is desirable so the larger lens sizes are useful.

    Dale

  12. #12
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    in theory yes, but i suspect the difference in usable range between a 40 and 50 obj (all else equal) is not that much?

    much depends on the quality of the optics........etc

  13. #13
    Sharp Shooter
    The Professor

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    Hardy,
    A while back I had a 3-9x50 Leupold (non P/A Vari X-II) and setting that up for airgun distances it gave noticeably less depth of focus than a Bushnell Trophy 3-9x40 set up at the same distance.

    Dale

  14. #14
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    arrh, so it really makes a difference.............what are we talking about here Dale? 5m? 10m?

    tks

  15. #15
    Sharp Shooter
    The Professor

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    Setting parallax of both scopes at 35 yards on 9 mag, the 3-9x50 was noticeably less clear past 45 yards than the 3-9x40 (and an equivalent at closer distances).

    Dale

    <span class='smallblacktext'>[ Edited Fri Oct 21 2005, 09:50AM ]</span>

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