50 or 56 nightforce

Discussion in 'Long Range Scopes and Other Optics' started by eyeballjr, Jan 21, 2011.

  1. eyeballjr

    eyeballjr Well-Known Member

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    I am looking at getting one pretty soon(5.5x22), for you guys that are in the know about this stuff, is the gain of using the 56mm worth the added height, or should i just go with the 50mm objective lens.
     
  2. SBruce

    SBruce Well-Known Member

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    Kinda depends on if you've got a long heavy barrel magnum or a lighter slimmer gun? If you've got an adjustable comb or high comb stock?

    If you prefer light and low pro go with the 50.

    The 56 will give you an additional .25mm of exit pupil or about 3.5% of usable light.
     
  3. Topshot

    Topshot Well-Known Member

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    I have a 56mm on mine and I need every bit of it in poor light on 22 power.
     
  4. ScottCoulter36

    ScottCoulter36 Member

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    Whether you go with the 50 or 56 is going to mainly depend on what kind of shooting/hunting you're going to be doing. If you hunt in heavily wooded areas or in places that are often gloomy, and don't mind the extra 1/4" or so in height, then go with the 56.

    I actually called nightforce last night and had alot of questions for the guys before I personally decide on a scope. The rep said he has this scope in 50mm on his 300 rum and has never had an issue with light. I asked him about the light transmission difference between the two and he said it's practically not noticeable.

    So my opinion from that is that if you are using this as a hunting rifle, go with the 50 for less height and the tiny bit of less weight. If you are bench shooting, you might as well get the 56 since it's the same price anyways.

    Good luck with your choice, and let us know what you decide and how it worked out as I'm planning on buying a scope in the next month or two,
    Scott
     
  5. zupatun

    zupatun Well-Known Member

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    Hi folks I'm confused. A 56mm obj has about 2462 sqmm area to gather light. A 50mm obj has about 1962mm sq. That's about 25% more area than the 50. How does it end up at only 3 plus percent or so?

    Matt
     
  6. Gary Kaney

    Gary Kaney Well-Known Member

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    My question is why do they even put the 32 mm out? I bought one and wish i had my money back. I'm not a fan of the 50mm, 42 or 44 is ideal .
     
  7. jmden

    jmden Well-Known Member

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    This is the same thing that one of the NF vendors here on lrh.com told me when I was looking. Not enough difference to be noticeable for hunting purposes. If you are a real mil or le sniper, the 56 might be your ticket. Just an fyi though, Shawn Carlock (BTW, Shawn is an NF Master Dealer...hint...hint) told me to get the 56mm and Kirby Allen (he built my 338AX) said 50mm is plenty for any legal light hunting situation. I went with 50mm as I was putting together a packing gun and every ounce and bit of extra size counted for me.
     
  8. eyeballjr

    eyeballjr Well-Known Member

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    Sounds like the 50mm objective is the way to go as this rifle is a hunting gun. Doesn't sound like you gather enough light to make a difference one way or the other.
     
  9. Michael Eichele

    Michael Eichele Well-Known Member

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    After owning several 56mms and a couple of 50mms, I will take the 50mms every time or even less when available.

    For a hunting rifle, 50mm is plenty and the lower profile and less weight seems like a better bargain. But that is just me. I may feel differently with a bench rifle since weight and size is of NO concern.

    M
     
  10. CRNA

    CRNA Well-Known Member

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    I looked through the 50 and with 22 power the light was, in my opinion, too dark. The sight picture had a blue hue to it. I went with the 56 and it is clearer at 22 power. My vote goes for the 56 due to the amount of light let in.
     
  11. SBruce

    SBruce Well-Known Member

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    Matt,

    Exit Pupil is the term used for the amount of light that makes it to our eye, it's measured in millimeters and is based on the diameter of a circle. It is determined mathmatically by taking the objective diameter divided by maximum scope magnification.

    Hence, 56/22 = 2.55mm, 50/22 = 2.27mm. Difference of .28mm.
    They say that supposedly, 7mm is the maximum amount of light that our eyes can benifit from/use; because our own pupils only dilate to about 7mm in the dark. That's where the really old 7X50 and 8X56 Binoculars came from. They are the brightest exit pupil our eyes will notice.

    Now this is maybe where it gets confusing, depending on how we want to look at it. .28mm is 12% of 2.27mm exit pupil (or 12% increase). But it's only 4% of the 7mm our eyes can use.

    Sorry for any confusion.
     
  12. Topshot

    Topshot Well-Known Member

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    SBruce,
    Don't get confused between exit pupil size and total light transmission. The focus point of the scope may be only 2.55mm or 2.27mm on 22 power, depending on the objecctive lens size. But this is only a measurement of the diameter of that point of light. It does not tell you how much LUX is contained within that point of light.
    A 56mm objective lens will have a larger focus point, but just as important, that focus point will contain much more light (LUX) that has been harvested by the larger lens.
    This is a factor that not even a lot of scope salesmen understand.
     
  13. SBruce

    SBruce Well-Known Member

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    Interesting, I've heard of total light transmission, but have never seen a way of measuring/calculating it or any advertisement specs on it. Lux is a new word too.........That's why I love this sport, always something new to check out!:)

    So far, what I've found is that light transmission is also dependant on the amount of lenses inside the tube and the type of coating used on the lenses. Also, according to Leupold; some coatings are better than others for the particular wave length of light that is present during dawn and dusk. Additionally, there are certain wavelengths that are visible by the human eye, and others that aren't..........So, lense coatings should be designed to transmit as much of the human visible wavelengths as possible..........not just a sum of any and all wavelengths.

    Alot of scope makers say that they transmit XX% of light, but what percentage of that light is visible to the human eye??

    Something else that may be of interest is Twilight Factor (which can be calculated).
    Twilight factor is the measurement of the efficiency of a rifle scope in low light conditions. The higher the twilight factor, the more useable the scope is in twilight conditions. The formula for determining twilight factor is: The square root of magnification times the diameter of the objective lens. Coatings and glass quality are not represented in this figure.

    Roughly the same results from this calculation as for exit pupil. The 56mm has 12% more twilight factor.
     
    Last edited: Jan 22, 2011
  14. Topshot

    Topshot Well-Known Member

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    Some technical stuff.....................................From our mates at Wiki.

    The lux (symbol: lx) is the SI unit of illuminance and luminous emittance measuring luminous power per area.

    In SI derived units these are measured in lux (lx) or lumens per square metre (cd·sr·m−2).

    In short, what goes in must come out. (minus losses). A bigger objective lens captures more light, has a bigger focal point and just plain looks brighter in poor light. This may give you five minutes more shooting light just on dark and a brighter image in dull light at other times.