Explain to me (newbie) about scopes & optics.


July 16, 2004, 06:47 PM
Hey, it's me the gun newbie again. (Odd because I'm a Senior Member here!)

I have a question about scopes. To ask this question I will give a true life example:

When I get my AK-47 (SAR or WASR), I plan to eventually get a PSO 4x24 V-1 scope. Now, what does 4x24 mean? I've seen these kinda numbers like with the SOPMOD M4 having a 4x scope.

So to recap, what does 4x24 and/or 4x (for the M4) mean? I think it's the power of the scope, but how is that measured? Don't hesitate on using any fancy words on me.

Thanks for all the help.

(I also plan on getting a Kobra sight, but that's a red dot sight, which is pretty self explanatory.)

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July 16, 2004, 07:12 PM
The first number is the magnification. The second number is the diameter of the lens in millimeters (the lens at the muzzle end of the rifle, not the one near your eye).

So the scope you're looking at has a 4x magnification with a 24 mm diameter lens. Something at 100 yards would appear to be at 25 yards.

If you see a 3-9x42 scope, that means it can magnify from 3 times to 9 times with a 42 millimeter diameter lens.

One thing to be careful of when selecting a scope (there are lots of things but this one is important to me) is the eye relief. It's how far away your eye can be from the scope and still see the image. Longer eye relief the better (for me at least).

July 16, 2004, 07:22 PM
Yes the 4x is the magnification. The image or target will appear 4 times greater in width (and height). This also makes it appear 4 times closer.

The 24 is the objective lens diameter. The size of this lens determines the light gathering ability and thus the image brightness. Although there is no additional brightness gain beyond a certain size. Because of the exit pupil.

Woodbridge? Do you shoot at the range in Stafford at all?

July 16, 2004, 07:53 PM
Doesn't the lens diameter -- the 24 -- correspond to the width of the view through the scope, so with a 4x20 you would see a smaller 'picture' than a 4x30, but more than a 4x15?

Someone even told me (so it could *easily* be wrong) that the 24 was how wide in feet that the 'picture' was at 100yards. True? False?


July 16, 2004, 08:11 PM
Ahh... thanks guys. That explains a lot.

So, a 3 - 9x (like the example Cacique500 brought up) would be a scope that could zoom in/out?

July 16, 2004, 08:49 PM
Roc_Kor -

Yes, two numbers before the "x" indicates the range of magnification, in that case, variable from 3x to 9x.

blackdragon -

You are referring to "field of view" which is more related to magnification than objective diameter. The 24 indicates a 24mm objective. I suppose it's possible that the field of view could just happen to be 24 feet @ 100 yds; but that would be coincidental.
Consider a variable power scope. As you change the magnification, the field of view will also change, becoming smaller as power is increased. But the objective is staying the same.

July 17, 2004, 06:05 AM

The objective size has nothing to do with the field of view, only with the size of the "exit pupil" and maximum attainable resolution of the optical system. The exit pupil basically tells you how much usable light you can get into your eye from the scope and exit pupil = (objective size)/(magnification). So a 4x20 scope has a 5mm exit pupil. Your eye can dilate to approx 7mm, so there is no brightness gain for getting an exit pupil any larger than 7mm. This is why the (generally more optically savvy) European folks prefer fixed power scopes like the 6x42 and 8x56. Variable power scopes (such as your 3-9x42) offer versatility, but there are drawbacks. The optical system is not as robust, the system is heavier, and the image sucks at the lower magnification settings as it ALWAYS suffers from curvature of field distortions, something no scope maker (to my knowledge) has addressed. It makes the image look like it's being viewed through a goldfish bowl. I guess they figure us shooters are a bunch of optical slackers (and they're probably right).

July 17, 2004, 05:35 PM
Looks like everyones given you great info on scope nomenclature. One thing to watch out for. though, is that some scope manufacturers, including older Leupold (since corrected), mislabled their scopes with IDs like '3X9-40' or '4X12X40', etc. In any case, the last number is the objective diameter.

July 17, 2004, 08:30 PM
Thanks all!


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