Numbers on a scope

msmalley1227

February 02, 2012 21:03

This may sound like a dumb question and probably is but here goes. When reading the description on rifle scopes they will have different numbers like 4 x 30. What do these numbers mean? Thank you.

Mike S.

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  Tflogger

  February 02, 2012 21:48

  The first number is the power of the scope, 4X means it's 4 times more than the naked eye. The second number is the diameter of the objective lens in millimeters.

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  TWalker

  February 03, 2012 02:01

  Tflogger is correct. There is an exception, however. On my German made, Pecar brand scope, 4x81 appears on the eyepiece. 4 is 4 power magnification, and 81 is a relative brightness rating, not the objective size that the second number normally represents.

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  tsr1965

  February 03, 2012 02:19

  The advice you have seen so far is correct. However, there is more. You may see the 4x40, or 4x32 in the case of a fixed power, but in the variable you will see 3-9x40, or some similar arangement like 4.5-14x40. The first number like 4.5 is the low poawe setting, and the second number like 14 is the high power, and the 40 is still the oblective lens(the lens closest to the object you are aiming at) diameter, in mm(millimeter's).
  
  Now all of that said, since you are looking at using this in the twilight, or perhaps even dark hours, you will want to know a little about exit pupil. The pupil of the human eye, can dialate to 5-6 millimeter's in diameter, during low light conditions. We most commonly say 5mm of maximum pupil dialation. The exit pupil of an optic, is how much image light exits the ocular lens(lens closest to the shooter's eye). It can be calculated by dividing the objective lense diameter by the power setting. In the case of the 4x30, the exit pupil would be 30 divided by 4, which is 7.5. The variable power scopes, the exit pupil is also variable, dependant on what setting you are on. The lower the power, the bigger the exit pupil. So that is something to keep in mind also.
  
  One last thing...In optics, there is no other way around it, and some will say that inexpensive brand x is excellent, and blah, blah, blah...The real deal is, that you really do in 99.9% of the cases in optics, get what you pay for. For that reason, I usually start with Burris FullField II as the bottom end for me, and go up from there.
  
  Best

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