If the eye relief sux then it does not matter how good the glass is or size of objective lens is to me.
I don't want to struggle for target acquisition.
Just to keep confusion to a minimum....
(A) Eye relief is the distance that they eye should be from the ocular lens in order to see the full scope image. It usually is a range, and commonly somewhere between 3.0" and 4" from the ocular lens.
Eye relief is different for every scope, but since airguns don't have much recoil, this is not of huge importance (but it would be for a rifle with high recoil, because a short eye relief of say 3" could give you "scope eye" —
black & blue from hitting your eye because it was too close for the heavy recoil).
(B) Eye box is this illusive "box" that the shooters eye has to be "in" —
in order to see the full scope image without any shadowing at the edges. ▪The
smaller the eye box the more the shooter has to keep his/her eye in the same position to keep the full scope image (
"finicky eye box"). The
larger the eye box the more forgiving it is when the shooter moves the eye a bit (
"forgiving eye box").
▪A
bench rest shooter can deal much better with a finicky eye box than a
hunter that is trying to get a
off-hand shot on a moving squirrel.
▪"Eye box" is not a spec that is given by the manufacturers.
However,
the eye box does depend on the size of the exit pupil of the scope. And that is a spec that is either given, or can be calculated (divide
objective lens diameter by the magnification used).
This brings us back to the topic of this thread — objective lens diameter....
▪I'll attach a PDF with a short
table that already has the calculations of the exit pupil size done — for 8 objective diameters and 15 magnifications.
View attachment SCOPE Exit Pupil Size Recommended. 02.1611383827.pdf ▪The recommendation is that
the exit pupil size should not be smaller than 2.0mm to avoid a finicky eye box, and larger than 3.0mm is much more forgiving yet.
(C) Target aquisition has to do with how wide your
field of view (FoV) is at the range where you try to find ("aquire") your target.
Try to "find" a squirrel at 15 yards, with a 20x magnification scope...! Very hard to "aquire" because your FoV is so narrow.
The same squirrel at 100 yards, with 20x magnification, shouldn't be so hard!
▪For quicker target aquisition
when stalking and hoping to stumble upon prey
at very close range I would recommend a
FoV of at least "30ft at 100y". Many scopes at 3x have that kind of FoV.
Hope this clarifies some of the finer details of scopes.
Matthias
