Those numbers mean something.

Discussion in 'Optics & Mounts' started by Shihan, Jan 25, 2011.

  1. Shihan

    Shihan Active Member Lifetime Supporter

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    I can look at a tire an see, P225/60R16 63H M+S and I know it is a Passenger Tire with a width of 225mm, an aspect ratio of sidewall to width of 60, it is a Radial with a wheel diameter of 16 inches, load rating of 63 with an H speed rating(130mph) and M+S denotes All Season driving.

    But if I see, 3-12x50, I have no idea. Break it down for the Layman.
     
  2. Gatekeeper

    Gatekeeper New Member

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    3-12 X 50 would be
    3 to 12 variable power magnification X 50mm Objective lens diameter

    4.5-14 X 40 would be
    4.5 to 14 variable power magnification X 40mm Objective

    etc...
     

  3. c3shooter

    c3shooter Administrator Staff Member

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    And a fixed power scope (like the little bitty .22 scopes) would be 4x15. 4 power, 15mm objective lens.
     
  4. Shihan

    Shihan Active Member Lifetime Supporter

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    How about a little primer on how to choose the proper power for different applications. Let's not be brand specific. Just say I want to shoot 500 yard with a rifle what power would be good.

    What about objective lens size? What would I want 30, 40 or more? Would it be similar to a telescope the bigger diameter the more light is gathered?
     
  5. jpattersonnh

    jpattersonnh Active Member

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    Depends on the qaulity of the glass!!! I have old 4x scopes that will do it, and new 4x scopes that it is way past their ability.
     
  6. DrJason

    DrJason New Member

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    What is the importance of the objective lens diameter? Is larger better? As magnification changes does the importance of lens diameter change?
     
  7. willfully armed

    willfully armed New Member

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    larger the objective, the more light that comes in.
     
  8. jpattersonnh

    jpattersonnh Active Member

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    Not if you use a high powered scope! As you increase magnification it diminishes light.
     
  9. Gatekeeper

    Gatekeeper New Member

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    See "Exit Pupil"
    Optics - The Advantages of a Large Exit Pupil

    The Advantages Of A Large Exit Pupil
    By Hugh Birnbaum
    A significant characteristic of an optical viewing instrument is the diameter of the exit pupil. The exit pupil is the circular patch of image-forming light the instrument presents to your eye. If you point a riflescope toward a brightly lighted wall or a patch of clear sky (but not at the sun!) and position your eye about 10 inches from the eyepiece, along the optical axis, you will see a bright disc of light in the center of the field. That disc is the exit pupil. The larger it is, the brighter the viewing will seem, because more of your eye will be bathed in light.

    You can calculate the size of a scope's exit pupil by dividing the effective objective diameter in millimeters by the magnification. For a 4X 32mm hunting scope, divide the 32mm objective size by 4 and you find that the exit pupil is a generous 8mm in diameter. With a 6.5-20X 50mm target/varmint variable scope, the exit pupil ranges from a large 7.7mm at 6.5X to a smallish 2.5mm at 20X. In a low-light situation, all other factors being equal, a lower magnification setting will provide seemingly brighter viewing than a higher one.

    It is tempting to conclude that the largest obtainable exit pupil is the most desirable. But that's not always the case. The catch is that the pupil of a normal human eye opens to a maximum diameter of 5mm to 7mm, depending on the individual, even in extremely dark surroundings. Exit-pupil diameters that exceed about 7mm deliver more light than your eye can accept.
     
  10. c3shooter

    c3shooter Administrator Staff Member

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    Early "night glasses" were binocs with a large exit pupil- matched up to your eyes at night. You got to use more of the light, and could see better in dim conditions.

    In GENERAL, the more glass inside the scope, the more light gets soaked up by the scope- but coatings on the lenses, composition of the lens itself and the stickum that attaches one bit of glass to another makes a difference- and large objective (front) lens DOES gather more light- but what happens to light inside scope is another matter.

    Then there is color, distortion near edges, field of view, yada yada yada. Like most things, you get what you pay for. There is a reason that a $500 scope is a $500 scope. But frankly, you don't always NEED a $500 scope. Durable and reliable, yes. But for a 30-30 lever?

    One simple test of a scope is squaring the box. Zero scope. Then 10 clicks up, 10 right, 10 down, 10 left, then shoot. Still zeroed?

    Too MUCH magnification can be bad- dimmer, small field of view- for hunting, at 200 yds, with a 24X scope, I would not be able to find the deer! for 500 yd shots on a groundhog, good scope.
     
  11. cpttango30

    cpttango30 New Member

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    First determin what you want to shoot with said rifle. A deer rifle out west is different than a deer rifle back east. I will talk about Varmint hunting as I know blasting small furry critters into little bits of red mist.

    Ground hog are rather big for varmints. Most range from 100 to 400 yards. You can take on them with a scope as small as 3-9x40mm. Some prefer a little more power so they jump to the 4-16x or 4.5-15x. My two varmint rifles have big scopes one is a 6-24x and the other is a 6.5-20x. You want to avoid anything over about 20 or 24x for varmint hunting really. But If you are trying to bullseye a p dog at 1k then buddy bigger is much better. You are going to want to really look at a nightforce 12-42x.


    For me shooting 500 yards 20x is as low as I would go. some will say more some will say 3-9x will work for everything. Sure it will kill a deer at 500 but to me that is taking pot shots. The Military says 1x per 100 meters. So as to not over scope yourself. Remember the more power you have the less field of vision (FOV) you have. 500 yards 6-24x40mm would be good in my eyes. I love the 6-24x40 or 50mm can you tell.....


    Objective size is not the be all end all that many make it out to be. Tube side and the size of the lenses in side are what make a big difference as well as the glass quality. If you take a 6-24x50mm Nikon Monarch and set it next to a 6-24x50mm Basaka and look through them you are going to see a big difference. Objective size range from about 20mm to 72mm with 40 and 50 being the standards. The bigger the objective the more light is allowed to enter the scope. If you have a 50mm obj on a 1" tube your going to lose some light transmission do to the small tube. If you have a 40mm on a 30mm tube with 30mm lenses in the tube you will have a brighter scope that the 1" but you will have the same amount of adjustments. Glass quality and coating quality do just as much or more than objective size.

    Yes See above.
     
  12. c3shooter

    c3shooter Administrator Staff Member

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    One minor point for VERY long range shooting- range of adjustment. Depending on the range and the caliber you are using, it is possible to run out of clicks of adjustment (now, lemme see, for the 45-70 at 900 yards, I'll need to hold over about 37.5 feet.....)
     
  13. Jpyle

    Jpyle New Member

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    Yes and no...a bigger diameter objective will indeed allow more light in for a brighter target view but just like a telescope, low quality lenses will causes distortion around the edges and blurring. Generally I believe a lower powered scope is more forgiving at lower price points than a large objective, higher magnification scope; high precision lenses cost big bucks to grind. Of course mechanically holding zero is another issue independent of the lense quality but does effect price.

    Certainly I am not the expert here just extrapolating what I do know from astronomical refractor scopes which is basically what a rifle scope is.
     
  14. M14sRock

    M14sRock New Member

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    Getting the light in (Objective lens size) is one thing, but getting the light transmitted to your eye is an entirely different thing.

    A fixed power scope of a certain quality will transmit more light than a comparable variable power scope on the same setting, all other things being equal.

    High quality glass makes the difference, and good lens coatings are critical.

    That said, the application should determine the power range used. I prefer lower power ranges for overall use, while many prefer higher settings.

    On a ground squirrel cull last spring I never set my scope (Meopta 4-16x44) higher than 6x, even on shots out to 380 yards, and never had a problem. YMMV.