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Low light clarification

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/13/2009 at 20:35
charlie09 View Drop Down
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I have read on this forum different opinions on the objective diameter affecting the ability to see in low light so i want to clear up this matter before  I buy a new scope. I want a low power variable or fixed scope to go on an ar-15 but most have a smaller objective than say a 3x9x40, I've always heard that you need atleast a 40 mm objective to see in lowlight, is this true or will a smaller objective be ok as long as it is set on low magnification.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/13/2009 at 21:21
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The two are dependent on each other. So, for example, if you have a 4X scope with a 33mm objective the exit pupil will be 33/4 = 8.25mm. That exceeds the maximum amount that the normal human eye can see. And that's in a young person. You could put a pretty small scope on there (like a 1-4x24) if that's all the magnification you need and still have a minimum exit pupil of 6mm.

The other major factor is glass and coatings. The better they are the more light is transmitted and sharpness/clarity go  a long way in low light situations.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/13/2009 at 22:20
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I have been working on this subject as well.  Most people say that the 40mm (or more) does help in low light, but just a bit when you go past 40mm.  I think that I understood that keeping it on low power does improve light transmission.  It is well understood that more high end scopes will do better in low light. So if you spend alot you can get a better small scope than cheaper large one. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/14/2009 at 07:52
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Check out the Zeiss Conquest 2.5x8x32.  Surprisingly good low light performance.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/14/2009 at 08:58
Dale Clifford View Drop Down
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still depends on the range of the target, shooting at rabbits and such on a moon light desert night on 12x is a lot different than shooting at night in the trees. As jono pointed out a 5x with a 28 bell will give the same results as 5x with a 40, (all things being equal) because of the physiological limitations imposed. The glass used by some manufactureres (high end) has been formulated for max. light transmissions in certain wavelengths, which help in low light and with the addition of coatings and better internals give better performance. Question- is do you want to pay for it?

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/14/2009 at 17:57
charlie09 View Drop Down
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Thanks for all the replies and I am highly considering the zeis 2.5x8x32 with a #4 recticle but if I decide to go with something else then is it true to say that as long as the objective diameter devided by the magnification equals 6 or greater and has good glass and coatings then it is as good as it can get and not just dependant on the objective diameter.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/14/2009 at 18:06
Urimaginaryfrnd View Drop Down
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Bright Scope means 7mm exit eye pupil so to be bright a scope must have larger objectives if it has higher power.
 
1x  7mm objective
2x  14mm
3x  21mm
4x  28mm
5x  35mm
6x  42mm
7x  49mm
8x  56mm  --- once you get past that they become rather clumsy.
You can take a variable and dial down the power in low light to brighten the image.
Example  4-16x40  will be bright at  4x or 5x or 6x  and if you went to 4-16x50 all you are gaining is one more power  7x that will be bright so is the cost and height of the scope worth it?  Sometimes it is like with trijicons 2.5-10x56 which even at 10x has a 5.6mm exit eye pupil  which is fairly bright its not 7 but 5.6 is pretty darn good in low light and the illuminated tritium & fiber optic reticle make that an outstanding low light optic.
Trijicon 2.5-10x56 Accu-Point 30mm Rifle Scope Amber Triangle Trijicon 2.5-10x56 Accu-Point 30mm Rifle Scope
Stock # - TR22
  • Matte
  • Amber Triangle
  • 30mm
$806.95
Add Trijicon 2.5-10x56 Accu-Point 30mm Rifle Scope to Cart 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/14/2009 at 19:40
charlie09 View Drop Down
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Thanks for the info.
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