low light

[bodiebill]

Will a 50mm objective scope be better than a 40/42mm in low light?
How does exit pupil relate to improved efficiency in low light?
I see some scope manuf list transmitted efficiency for scopes. Is this a more relevant factor than objective diameter?
What are the best low light scopes and why?

 

[matrem]

1 Given equal glass & magnification.. Yes
2 Exit pupil should be at least the diameter of your pupil.
3 Yes. Glass quality.
4 Top quality glass with exit pupils as big as yours.

 

[rcmodel]

A young human eye can use a maximum of about a 7mm exit pupal.
More then 7mm can't be put to good use because the ires in your eye won't open any wider then about 7mm.
Low light ability relates to the size of the exit pupal.

That is determined by the objective lens dia. divided by the power of the scope.

A 3x-9x x 40mm would have 13.3 exit pupal at 3 power, and only a 4.4 at 9 power.
A 3x-9x - 50mm would have a 16.6mm EP at 3x and a 5.6mm exit at 9x.

So, a 40mm scope at 6x is as bright as your eye can use.
And a 50mm at 7x does the same.

But other important factors include the quality of the lens glass, the quality of the lens coatings, and internal construction of the scope.

You could expect much better light transmission on a $750 dollar scope then on a $75 dollar scope.

However, with that all said, there is a much closer gap in lens quality between cheap & high priced scopes now then there was 25 years ago.

rc