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Variable Scopes, Low vs High

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/06/2004 at 14:42
DAVE44 View Drop Down
Optics Journeyman
Optics Journeyman

Joined: November/11/2004
Location: United States
Status: Offline
Points: 652
     I know that Low powered variables tend to be a tad lighter and shorter, but are there any advantages other than field of view or size and weight to having a smaller scope? I mean they seem to cost more than higher powered variables while at the same time they have smaller objectives and it would seem like they would do worse in low light. Why dont they make more low power scopes with larger objectives than say a 32mm or 36mm. Just curious, is it just that way so they can mount lower?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/06/2004 at 14:48
Boomholzer View Drop Down
Optics Apprentice
Optics Apprentice

Joined: June/20/2004
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I believe that the scope's exit pupil is already optimal to the human eye. 

Increasing the objective size of a low power scope will not allow any more light than possible given the lens coatings and the human eye.


I think that around 7mm is the maximum the human eye dilates in low light conditions.

Edited by Boomholzer
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/06/2004 at 17:06
Chris Farris View Drop Down

Joined: October/01/2003
Location: Texas
Status: Offline
Points: 7790

Boomholzer is correct and to further elaborate for those that don't know what an exit pupil is or how to determine it....


Exit Pupil
The size of the column of light that leaves the eyepiece of a scope (usually measured in millimeters).  The larger the exit pupil, the brighter the image.  To determine the size of the exit pupil, divide the objective lens diameter by the power of the scope.  IE; a 4x32 scope would have a 8mm exit pupil.  32/4=8.


The maximum the human eye can perceive is 7mm in total darkness.  As you get older you pupil will only dilate to 6mm then 5mm.


A scope with an exit pupil over 7mm is great for quick shots because the exit pupil is larger than your pupil and you can get a full picture faster.


1.5-6x42 is perfect in low light on 6x.  42mm objective/7=6

1-4x20 is perfect on 2.86x or 3x basically  20mm objective/7=2.86


A 1.5-5x42 would transmit the perfect 7mm exit pupil on 6x and it only goes to 5x.  42mm/7=6


So that is the reason why low power scopes have small objectives (they don't need big ones).

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