Scopes?

Discussion in 'Long Range Scopes and Other Optics' started by kc, Dec 29, 2009.

  1. kc

    kc Well-Known Member

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    I find many scopes that are 3x9x40, now there is a 2x7x32 and I am asking do you have or know of any low lite problems.
    All of my bolt actions use a 3x9x40s and they are on 4x most of the time. they work fine unless
    they don't stay in zero. Never had a problen with Burris, I can leave my rifle locked for a season and it will be on, every time.
     
  2. Chas1

    Chas1 Well-Known Member

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    kc, do you have or know of any low lite problems-that's a braod question with so many scope manufacturers out there so do you have any particular brands in mind. I've used Bushnell, Leupold and NF w/o any low light issues. Note the Bushnell was 3-9 so even at 9 I was ok with it.
     
  3. LouBoyd

    LouBoyd Well-Known Member

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    For any magnification up to the point where the objective diameter divided by the magnification is is a larger diameter than you're eye's iris there is no increase in image brightness by having a larger diameter objective. That's just a fact of optical design.

    The thing which separates high quality optics from run of the mill optics isn't image brightness or resolution or magnification. It's more image contrast. Image contrast is ruined by stray sunlight scattering inside the optical device. Of course reduced contrast can also be caused by light scattered by the atmosphere. Color correction is annoying in cheap optics but it's rarely bad enough even on cheap Asian scope to have any affect on the ability to aim a riflescope.

    The human eye has a large range of ability to handle image brightness. There is a period of time shorty after sunset lasting about 10 minutes where a larger objective can have an advantage by providing more light. When the available light drops to the point where color vision stops showing distinct color a human eye's resolution drops by a factor of over 10 because the low light rods in the eye are much sparser in the fovea than the color sensitive cones. At that point huge objectives lenses (50 to 80 mm) with magnifications of 10 to 20 magnification can be of some use giving the ability to see almost much resolution in moonlight as you could see naked eye at sunset. More practical is is to use a night vision scope or a spotlight.

    Personally I don't see any point in high magnification scopes. They have a place for benchrest shooting but not so much for hunting. Lower magnification gives a larger field of view and (usually) quicker taget acquisition as long as there's enough magnification to recognize the target. 2-7 and 3-9 power scopes are popular because they work fine for most hunting applications. Bigger does not mean better and are just more weight to carry. One reason not to have a large objective on a low power scope is that it has a larger exit pupil. That allows the eye to be far off axis without noticing it and that causes more parallax error if the scope isn't perfectly focused.

    Do you need a high resolution riflescope? In my opinion a riflescope should be selected for aiming the rifle not for sightseeing and finding game. A "normal" eye can resolve 1 moa. How much magnification and resolution is of benefit to aiming? Searching for game is much faster using wide angle binoculars with less than 1"eye relief than looking though a riflescope with a 4" eye relief. You see over ten times more terrain at once with the binoculars. Monocular spotting scopes are as fast as binoculars but may not be as comfortable.

    Just some rambling thoughts...
     
    Last edited: Dec 29, 2009
  4. Chas1

    Chas1 Well-Known Member

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    Lou Boyd, didn't think you were rambling. Interesting reading and some good points. Thanks.
     
    Last edited: Dec 29, 2009
  5. kc

    kc Well-Known Member

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    Real good points. thanks guys. I have always used a 3x9x40 and I think I could go a bit smaller, most of my shots Hunting are from 30ft to 30 yards..I have only had two shot at 70 yards and it was a clean head shot on both.
     
  6. kc

    kc Well-Known Member

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    The reason I ask this question is I have a 3x9 on my .35 Marlin sc and I need to use a smaller scope I don't need a 3x9 its to big and it is always on 4x.
     
  7. LouBoyd

    LouBoyd Well-Known Member

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    You'll see no difference in brightness with a 3-9x40, 2-7x28, or a 1-4x20 scope with them all set at 4x magnification except possibly in low light with the 1-4x20 if you're young and your iris can open over 5mm in low light. For most adults it cannot. Assuming that the three sopes all have the same design except for the objective lens they'll all have the same field of view and the same eye relief distance. The exit pupil diameters will be 10mm, 7mm and 5mm respectively so the smaller scopes will have less tolerance to radial or axial eye position. If the scope is properly mounted on the rifle to match your hold that's not a bad thing. Smaller exit pupils reduce the amount of potential parallax error.

    It's an interesting fact of optical design that no telescope can make the apparent surface brightness of of an extended object brighter than looking at it naked eye. If the light source is too small (in angular size) for they eye to resolve it then a telescope can make the object appear brighter such as when looking at stars. Once an object is resolved (like looking at a distant street lamp), a larger and more powerful telescope will make the lamp look larger, but will not make it appear to have a greater surface brightness. The image though a telescope will allways be a little dimmer han naked eye because of internal reflections off the optical surfaces, though with modern optical coatings those losses are small.
     
  8. kc

    kc Well-Known Member

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    My eyes arn't like they were when I was a kid(55) in the winter I need sunglasses and I cant drive at night even with glasses its a blur. But they are sharp enough to spot a deer sneeking in a swamp.