Optical magnification, measuring?

D

Don

New member
What is the easiest and most practical method to verify a listed scope or camera lense magnification specification, as it relates to the optical view that the human eye sees?

So many camera lense magnification specs. seem to end up magnified alot less than the same magnification for a given gun scope.

Is there a "real world" tool or method that can be used to verify manufactures magnification specifications?

For instance, I have a 20x Leupold scope that easily views a 6mm bullet hole on target at 200 yards, no mirage, while my 20x optical lense Panasonic video camera will not view the same diameter at even 100 yards, same mirage conditions. Placing the 2 instruments side by side it is obvious the video camera magnification is greater than 50 percent less than the gun scope, although the manufactures both use the same optical magnification designation of 20x...............Don
 
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Optical and Digital zoom.

Have you looked at your panasonic video on a WIDE screen HDTV?

I am assuming your camera is the one that shoots in AVCHD format?

Paul
 
Don:

I don't know the answer to your question, but I recently discovered this site which explains why certain archery lenses can yield apparently different magnifications based upon the distance of the viewer's eye from the lens.

http://www.sureloc.com/faq/diopters.pdf
 
All lenses do

Mike Marcelli said:
I don't know the answer to your question, but I recently discovered this site which explains why certain archery lenses can yield apparently different magnifications based upon the distance of the viewer's eye from the lens.
Click to expand...
My eye doctor explained that to me years ago when I was having trouble selecting the correct correction to use in my shooting frames. It seems that the standard frames they use to test eyes hold lenses 8-9 mm from the eye & my Champions carried the glass 29 mm from my eye. In my particular case, it gave me a +¼-½ dioptre correction towards my myopia.

Interestingly, they use a formula to adjust that result when they are setting you up for contact lenses which change the power because they're right on your eye.
 
I am sure I have noticed that if you wind the ocular lense of a scope all the way in the magnification seems to decrease a little ??????
 
A favorite of mine explained this to me not long ago. You divide the exit pupil into the objective lens diameter and the result equals the power.

Using "kitchen" lighting, you can focus the light from the eye piece onto white paper. Measure that, and divide it into the published objective diameter being sure to use like units..cm, mm, inches, etc...

Seems to work when compared to what the power is supposed to be on a given rifle scope.

But...the question comes to mind....20X what?
 
Wilbur is right

Wilbur is correct in stating that the power of a scope or binoculars is the exit pupil divided into the stated size of the objective lens.

The 20x on the camera states a ratio of the highest to the lowest focal length, and has nothing to do with the actual 'Power" of the lense.

After that, it is the quality of the optics, the contrast especially, that determines what will be seen.

Geary Koglin
Grand Blanc, MI
 
Hummmm

I was of the opinion that you divide the Focal Length of the scope assembly by the focal length of the eyepiece to get the power. The question is, what's the focal length of each. If you measure the focal length of the eyepiece, do you measure from the center of one of the lenses or from the rearmost ocular lens? I've tried to do this and failed to accomplish it with the desired results.

I'd also like to know of a good way to measure boost power.

Shelley
 
A factor that may complicate the matter of determining the magnification that we actually see (for some of us) is that corrective lenses have to be taken into account. If you are nearsighted, hold your glasses a couple of feet away from your eyes, and compare the size of an object viewed through one of the lenses, with the same object viewed without. It would seem that this difference is reduced as the corrective lens get closer, but that there is still some difference at the normal distance that they are worn. Do any of you wear contacts under your shooting glasses? If so, how well do they work as compared to glasses?
 
Shelley,

We are both right...If you know the the focal lengths, then you are right. When you know the size of the lens and the power,or the exit pupil size, then I am right too.

Geary Koglin
Grand Blanc, MI
 
Francis

FBecigneul said:
I understand the concept of image size on a piece of paper divided into stated ojective lens size. For the sake of measuring scope magnification in a Hunter or Varmint Hunter match, how far from the ocular lens should the paper be placed?
Click to expand...

You can see the right distance easily as it focuses. I made some circles with photoshop in millimeters to "overlay" the focused light. It's pretty hard to hold a scope focused on a paper with one hand and use calipers with the other. My circles were not fractional which resulted in a need to estimate slightly but for the purpose at hand it was OK.

The purpose was similar to that you mentioned, and I determined that I can take a quick walk down the line from a fair distance back looking at the "light hole" and tell if the power is excessive. Once you know what you're looking for it becomes easier.
 
Francis

Wilbur said:
You can see the right distance easily as it focuses. I made some circles with photoshop in millimeters to "overlay" the focused light. It's pretty hard to hold a scope focused on a paper with one hand and use calipers with the other. My circles were not fractional which resulted in a need to estimate slightly but for the purpose at hand it was OK.
Click to expand...

Francis,

I am not sure that Wilbur answered your question directly, what I have been able to piece together from these postings is that the "focus lense" is to be the same distance from the paper as the "eye relief" distance while using the scope during shooting, which provides a "full field of view" image in the focus lense. This will also coincide with the smallest diameter and most concentrated light circle on the paper refered to as "exit pupil" diameter.

For instance, I used a fixed 36x Sightron scope for my "Wilber experiment", found the "eye relief distance" to be about 2.75 inches from eye to focus lense, placed the scope 2.75 inches from the focus lense to the paper, made slight up/down adjustments until I got the smallest diameter and most concentrated light circle on the paper refered to as "exit pupil" diameter, which measured .050 inches in diameter, divided the objective lense diameter of 1.80 inches by .050 to get the 36x power specification exactly.

Wilbur is correct, its difficult to measure a light circle diameter with a dial caliper in one hand and holding the scope in other while trying to keep the scope in the optimal axial and height position............Don
 
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