A Question About Magnifying a Magnified Scope

[HGM22]

Out of curiosity, what happens when you magnify a magnified optic? Do the powers multiply?

I'm thinking particularly of a Vortex Strikefire with the screw-in 2x magnifier. What would happen if you then added a 3x flip-to-side magnifier. So, we have a 2x optic with a 3x optic. Would this result in an image of 6x?

 

[JSH1]

I've not done it with rifle scope but that is how it works with a telescope. I had 2X barlow lens that I used in conjunction with different powered eyepieces.

 

[zerobarrier]

That's how it works with a microscope. You have a 10x eyepiece and a 50x objective lens, overall magnification is 500x.

 

[Snyper]

Unless the distances and focusing of all the lenses is precise, you probably won't get the results you expect, and no matter what, it will drastically reduce the amount of light getting through

 

[Bart B.]

A 2X magnifier on the front of your rifle scope does the same thing if one's put on a camera lens; it doubles the focal length of the objective lens group. Your scope will have twice the magnification.

The real formula for a telescope, microscope or whatever is as follows:

Objective lens (group) focal length divided by eyepiece lens focal length equals magnification.

If objective lens has a 40" focal length and the eyepiece lens has a 2" one, the magnification will be 20X. That's how 20X scope sights work. But their objective lens groups is a "telephoto" optical type whose physical length is shorter than theiroptical length. A "long" lens group focal length is its physical one; mirror lenses for example.

http://www.rocketmime.com/astronomy/Telescope/Magnification.html

To find the focal length of your scope's objective lens group, multiply the magnification by 2 and the answer's what it is in inches. 7X scope multplied by 2 equals a 14" objective lens focal length.

Most scope sights' eyepiece have about a 2" focal length; that's how far the rear focal plane on its reticule is behind that reticle. Eye relief is different; that's how far back from the eyepiece you can see the full field in the reticule plane.

I've put a +10 diopter lens (4" focal length) on the +20 diopter (2" focal length) eyepiece of a 16X scope shortening the eyepiece lens group by about 1/3rd to 1.3 inches (then a +30 diopter eyepiece lens group). The diopter is a 40 inch or one meter standard in optics. Divide that standard by the + diopter number to get the focal length. - (minus) diopter lens' focal length are greater than 1 meter long. A -3 diopter lens has a 3 meter or 120 inch focal length). It raised the scope's power to about 25X. That also reduced the eye relief from 3 inches to 2 inches. On the rimfire 22, that wasn't a problem.