Author: koshkin
Subject: If everything is equal is bigger scope brighter?
Posted: September/24/2013 at 12:12
Subject: If everything is equal is bigger scope brighter?
Posted: September/24/2013 at 12:12
 ugapaul wrote:I am a layperson but through a little bit of reading, my take is: 1st one must define what pupil size the scope user has, say 5.5 mm. If the exit pupil of a given scope is larger than this value, the pupil can not utilize the excess. If you take two of the same brands of scopes, with the same glass and coatings, one a 40 mm and the other a 50 mm (not worrying about differing optical design), the results depend on magnification as to "brightness." At 2x, the 40 mm exit pupil is 20 mm and the 50 mm is 25 mm. Both appear equally bright since the viewers pupil size is 5 mm. At 5x, the 40 mm is 8mm and the 50 mm is 10 mm - both appear equally bright. At 8x the 40 mm is 5mm and the 50 mm is 6.25 mm. In this case, the 50 mm appears "brighter" because the 40 mm obj. at 8 x doesn't fully utilize the viewers pupil. As magnification grows above 8 x the 50 mm continues to utilize more of the viewers exit pupil. |
Generally, this is a well laid out argument.
I do have a few comments:
- Most scopes do not use all of the objective lens at low magnification. For example, the exit pupil at 2x of a 3-9x40 scope is a lot smaller than 20mm and how big it actually is varies from scope to scope. 10 -14 mm is pretty normal.
- Your eye pupil is constantly moving, so even if the exit pupil is a little larger than the eye pupil, your brain often gets additional information because the eye is effectively "scanning" around the exit pupil. This constant movement of the eye pupil is also needed to minimize eye strain. Fixing your eye in one spot is fairly unnatural and difficult.
- Human brain processes moving images better than stationary ones, so the slight movement of the eye pupil is an aid to visual acuity.
- The diameter of your eye pupil depends on how much light is coming in. If there is a lot of light, the brain naturally throttles down on eye pupil diameter a little. That helps cut down on aberrations due to the eye lens being imperfect and helps with depth of field quite a bit.
ILya