Light gathering capability with different power scopes....

[Ahsan Ahmed]

Since my experience/knowledge of rifle scopes is quite limited....

3x-9x(40) vs 4x-12x(40)

For use on Deer rifle in ON - where shots are generally always 100-125 yds +/- .....in my case, the opportunities to shoot along open fields or powerline corridors are much less.

A more powerful scope obviously means more magnification thus offering better details and clarity during failing light conditions. However, what I’m not sure is how much more light gathering capability that would equate to when compared between a 4x and a 3x scope.

I also feel a more powerful scope could perhaps be a hindrance in terms of distance under 100 yrds.

Therefore, my question.....which glass (from above two) will be the most suitable given my hunting conditions? Thanks,

 

[sir_springer]

Considering the nature of the country you hunt, while you can't go wrong with a decent quality 3x9, the 4x12 is a tad handier at range if it ever comes up. I like a bit more power around here because of point restrictions on both mulies (4 point) and elk (6 point). I check for these at least a couple more times before I pull the trigger.

Light transmission in a variable only decreases as you crank up the power. The difference between 3x or 4x is negligible. And I find there's little difference worth mention between 9x or 12x settings. Beyond 12x it gets exponentially dicier.

The two principle factors in light gathering, but more accurately stated, light "transmission" are:

a) Objective lens size. I prefer 40mm. Yes, 50mm is even better...if one doesn't mind a scope that kinda looks like a club attached to one's rifle. The actual difference between the two is so marginal, IMHO, as to not be really worth the usual extra dough the 50mm costs.

b) Quality of glass and especially coatings. Be certain that whatever scope you buy has "multi-coated" lenses, but "fully multi-coated" lenses are better yet. Light transmission can vary from as low as 85% in cheaper scopes with some lens coatings, to as high as 95% in quality scopes. This is probably the most important factor for you to consider.

95% transmission is about as good as it possibly gets on a "variable" scope, due to the extra lenses incorporated and basic physics. Fixed power can do a bit better.

You don't have to spend great big gobs of money to get good quality fully multi-coated lenses, and should be able to score something very decent in the $250 to $500 range.

Lastly, I personally recommend avoiding range finding reticles, particularly for the kind of hunting you're talking about. Can complicate things when the big moment arrives. Yes, they have their place in long range shooting for those who actually take the time to learn how to use them. Keep it simple with a duplex.

Considering all the work, time and cost that go into hunting, there's little valid argument for cutting too many corners on a scope.

 

[TheTooner]

Get the 3-9x40mm. If you can't see an animal well enough with 9x to shoot it, you probably shouldn't shoot. If you were a good enough shot to be shooting at the longer ranges you wouldn't need to be asking for advice on which scope to get. And for the typical hunting ranges you describe for your use, 3x rather than 4x as your lowest setting will be useful more often than having 12x rather than 9x for your highest.

A simple formula about light transmission in an optic: objective diameter divided by magnification equals exit pupil. E.g. a 4x 28mm scope has an exit pupil of 7mm. A 4x40mm has an exit pupil of 10mm. A 3-9x40mm variable has exit pupil ranging from 13.33mm on its lowest setting to 4.44mm on its highest.

The exit pupil is the size of the beam of light going into your eye. The bigger the exit pupil, the brighter the image, all else being equal, i.e. same quality of glass, same lens coatings. Up to a point.

That point being the limits of the human eye. In a typical young adult the pupil only opens to a maximum of 7mm, so in poor light, from the examples above the 4x28 scope has the biggest exit pupil your eye can use, and the 4x40mm has a lot of waste. As you age, your pupil opening is reduced. In your forties you'll probably only be able to benefit from a 5mm exit pupil, which you could get from a 4x20mm scope. Of course you can still use any size scope, it's just that if you are carrying around something with a great big objective bell to get a bigger exit pupil, it may be an inconvenience and a waste of money for no benefit.

Bigger objectives are needed for variable scopes. When you turn it up for more magnification, the larger objective lens still gives you a decent exit pupil, e.g. a 3-9x40mm scope on 3x has a larger exit pupil than you can fully use, but at 9x it's only 4.4mm.

But once you've figured that out, remember sir springer's points about quality, or you may end up with a very bright but poor quality image.