View Full Version : 50mm VS 60mm

05-12-2008, 10:09 AM
What would be the advantage of buying a 10-40x60mm vs a 10-40x50mm? Does the 60mm give more filed of view?

I am looking at two identical optics but one is 60mm and one is 50mm. price it about $45 diffrence.

05-12-2008, 11:10 AM
A larger objective gives better light gathering capability and a larger exit pupil, but also adds weight and makes for a tighter fit when mounting, depending on the rifle.

Whether the extra light gathering capability helps depends on the exit pupil. If the exit pupil is larger than the pupil of your eye, the extra light is unused, as it doesn't enter your pupil, but hits the iris.

This usually has the biggest impact when light is low, as your eye's pupil will be largest at this time, and will be able to make full use of the larger exit pupil. When the exip pupil is smaller than your eye's pupil is when a larger aperture would have helped.

So, at maximum zoom, one of these scopes will have an exit pupil of 60/40, or 1.5mm, while the other will have an exit pupil of 50/4, or 1.25 mm. Both of these are smaller than your pupil will generally be, so bigger is better.

At minimum zoom, the exit pupils will be 6 and 5 mm, which is approaching the size of the human pupil in low light (this is different for everyone, of course).


I'd say the extra size and weight would be a bigger factor for most people than the optical aspects, unless you're planning on a lot of low-light shooting.

05-15-2008, 8:20 PM
Maxicon is right about brightness and exit pupil. Also, what do you want a 40X scope for? The eye's optimum resolution occurs at a pupil diameter of about 2.5 mm. For a 40X scope not to limit resolution, the objective would have to be at least 100 mm. In other words, at 40X the 50 mm objective degrades visual acuity by about a factor of two.

Usually, only benchrest shooters feel they really need this magnification (to have the target fill the scope FOV). Unless you are in this category, you would be better off with a lower magnification range, say 4X-16X. For the same money, you could then go with a higher quality scope at a 40 or 44 mm objective and be way ahead in weight, brightness and resolution.