Re: 40mm vs. 50mm
rickg... <BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>There is no such thing as "light gathering". There is only light transmission. The objective diameter is governed by the type and magnification of the scope. The goal is to supply the proper exit pupil diameter through out the power range. Just because a scope has a 50 doesn't mean it put more light on your eye, could be the opposite. The criteria I use are coatings and exit pupil.<HR></BLOCKQUOTE>
Weeell... Not true.
Ask anyone that uses high powered scopes. The larger objective gathers more light than the smaller one. Whether your eye can use the increased light depends on the magnification the scope is set to, and the time of day (ie, the size of the pupil), that you are using it.
During the brightest part of a sunny day, the healthy pupil is about 1.5mm. This means that the most light the eye can accept is an exit pupil of 1.5mm... this means that the scopes power limit for full brightness is equal to objective diameter divided by the power, where the answer is equal or greater than 1.5.
With a 56mm obj, the maximum power is ~36x, but with a 40mm obj, the maximum power is ~26x. With long range shooters, or benchrest shooters, it is not unusual to use powers larger than 26x, and so even under the best conditions (for the eye), the larger objective "gathers" more light. If both were used at 26x, they would appear equally as bright, but if they were both used at 36x, the 40mm scope would appear substantially darker.
But... on overcast days, the pupil gets larger... typically around 4mm.
On a day like this, even at 26x, the 56mm scope would look much brighter, until the power was reduced to below 10x, at which point they would both look qually as bright... any magnification above 10x (which is not a lot), the 56mm would always look brighter.
The purpose of lens coatings is NOT to make the image brighter, but the make the shadows and dark areas appear darker.
I piece of cellophane only transmits 91% of the light... but it doesn't look dark when you look through it.
But if a scope has internal reflections from the lenses, (or reflections from internal parts), those bits of stray light cause a haze over the dark areas... and if you are looking for targets that are dark, hiding in the dark shadows, then the haze will mask them.
[ 08-24-2002: Message edited by: CatShooter ]
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