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Resoloution VS Light transmission

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/08/2004 at 15:15
DAVE44 View Drop Down
Optics Journeyman
Optics Journeyman

Joined: November/11/2004
Location: United States
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Points: 652
     I have read that scope companies have no across the board standard to measure light transmission. If that is true how is one to know which scope to get? For example if you look at the stats on a Burris Fullfield II and compare them to a Nikon Monarch they appear to equal in every way except their prices. Chris stated that RESOLOUTION is what makes one scope actually appear brighter in low light than another scope. I suppose that resoloution is what sets the Burris apart from the Nikon, so is the cost the only way a person is going to be able to determine how much better one is in low light than the other. All scopes appear bright during daylight hours so if one only hunts during the well lit hours of the day does one need a higher quality lense system of should he just save a hundred or so dollars and get the lower priced yet just as mechanically durable scope? Will better quality lenses help much during the middle of the day? I was planning of ordering an Elite 4200 due to the high praise it has received on this forum and for the RAINGAURD COATINGS. Do the 4200 Elites have better or equal RESOLOUTION than say a Nikon Monarch, Zeiss, Weaver GS or Leupold VIII. Or would you say they are about equal.
     I suppose I am just curious how much more shooting time a higher quality lens system is really going to add to your day.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/08/2004 at 16:37
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Optics Apprentice
Optics Apprentice

Joined: August/18/2004
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My guess would be:


vs. Monarch...a little better all the way around

vs. Zeiss Conquest...about the same, maybe not quite as good

vs. Weaver.....much better

vs. Leup VXIII....superior for alot less money


My swaro a-line 3-10x42 gives me about 10-15 minutes more shooting time than buddies VXIII.  It's really amazing when doing the comparison.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/16/2004 at 18:55
Chris Farris View Drop Down

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/16/2004 at 19:00
Chris Farris View Drop Down

Joined: October/01/2003
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Light Gathering and Clarity

Exit pupil and twilight performance are indicators of how well you will see an image at night combined with the glass and coatings.

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, with 6-7mm considered to be prime for the average user. To determine the size of the exit pupil, divide the objective lens diameter by the power of the scope. IE; a 10x42 scope would have a 4.2mm exit pupil. 42/10=4.2. If you are determining the exit pupil of a variable scope you must go about the formula a little differently. IE; 4.5-14x50 will emit a different size exit pupil on every power (11.11mm - 3.5mm). Simply determine what size exit pupil you want and divide that number into the objective lens and the answer is what power you need to set it on to achieve that exit pupil. To compare a 4.5-14x50 to a 10x42 you would need to put the 4.5-14x50 on 11.9x (50/4.2=11.9).

Your eye gathers more or less light as conditions change. The pupil is controlled by the iris which allows it to change in size from 2mm - 8mm depending on the light. As we grow older the maximum diameter that our pupil will dilate decreases. Most eyes dilate to about 7mm or 8mm at age 20, but only to about 5mm at age 50. Since the light gathering ability of a variable riflescope is changeable and the light gathering ability of a fixed power scope is fixed, it is important to compare them while they are emitting the same size exit pupil. A 56mm NightForce set on 10x will produce a 5.6mm exit pupil, a 4.5-14x50 Leupold will produce a 5mm exit pupil on 10x and the Super Sniper 10x42 emits a 4.2mm exit pupil. 6-7mm is optimum for low light performance. A difference of .5mm is substantial. Comparing a 42mm, 50mm and 56mm scope all set on 10x will benefit the scope with the largest objective lens. Another major factor in low light performance is determined by the scope's twilight performance.

Twilight Performance - During daylight hours the magnification will be the principal factor in image resolution. At night, when your pupil is dilated, objective size is the controlling factor. In twilight conditions both of these factors affect resolution. The twilight performance compares scope performance under these conditions. A higher twilight performance indicates that the scope will resolve images better under dim light conditions.

Calculate the twilight performance of a scope this way:

1) Multiply the magnification by the aperture
2) Find the square root of this product

According to this indicator, a Leupold 4.5-14x50 set on 10x which would be a 10x50 (twilight performance of 22.4) would resolve better than a 10x42 Super Sniper (twilight performance of 20.5). Remember, however, that the twilight performance will primarily indicate performance at dawn or dusk without consideration of the light transmittance or glass quality of the scope.

Super Sniper 10x42
10x42 = 420
20.493901531919196 x 20.493901531919196 = 420
Twilight Performance of 20.5
Exit Pupil of 4.2mm

Leupold 4.5-14x50 set on 10x
10x50 = 500
22.360679774997898 x 22.360679774997898 = 500
Twilight Performance of 22.4
Exit Pupil of 5mm

Here is where it gets tricky. You can resolve better in low light with a 3.5-10x40 set on 10x than you can with a 3.5-10x50 set on 6x even though the 3.5-10x50 set on 6x has a twice the exit pupil of the 3.5-10x40 set on 10x (8.3mm vs. 4.0mm). This is also why deer hunters prefer a 10x42 to a 7x50. Exit pupil is not the only determining factor in low light performance.

Leupold 3.5-10x40 set on 10x
10x40 = 400
20 x 20 = 400
Twilight Performance of 20
Exit Pupil of 4mm

Leupold 3.5-10x50 set on 6
6x50 = 300
17.320508075688774 x 17.320508075688774 = 300
Twilight Performance of 17.3
Exit Pupil of 8.3mm
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