Measuring/Comparing magnification. (1 Viewer)

[mekidear]

Is there any way of measuring the magnification of a binocular - without special equipment. Or just comparing different binoculars.

I know you can just look through them and see which appears to bring things nearer but I am not sure if 'field of view', 'brightness' etc have can give a false impression of actual magnification. I know with a narrow field of view, looking down a tunnel makes things look further away.

It is not important - I am just interested.

 

[jafritten]

Is there any way of measuring the magnification of a binocular - without special equipment. Or just comparing different binoculars.

Objective lens diameter divided by exit pupil diameter equals magnification. The problem is, how to measure the diameters precisely. I don't have the tools to do so. I'd like to know if there is an easy way to measure the magnification of a binocular.

 

[Dennis Mau]

From Cloudy Night's. https://www.cloudynights.com/index.php?findpost=63263

For magnification, see Henry Link's reference to Kimmo Absetz’s method of establishing a reading for a small power monocular:
Take a reading of a tape measure at some distance (75' to 100' away) using a monocular, then take a reading of the tape through the binocular with the monocular behind the binocular eye lens. [Used a small scope to accurately get a measure on a scale about 100 feet away (reading approx 14-15 feet). Then used the small scope behind each binocular to take another reading and divided the two values.] Division of the readings gives the power. All magnifications reported here use that method. It gives a fairly accurate reading, but because of it's relatively close (100 feet in my case) distance, all readings may produce magnification that is slightly (approx 1%) high. (In any binocular, Magnification usually varies by ~2% and by as much as 3%, from the closest focus to infinity). However, anyone trying this method would see that it can be quite accurate, and it is easy to measure power to tenths. Therefore, results are reported to 1/10th. All actual calculations produced values to hundredths, but there is no way that I can be measuring with that level of accuracy, so I have not reported it. It is impractical to measure using this method much beyond 150 feet, and in fact impossible to test using this method at infinity.
OR
Place one eye to binocular viewing a one-inch blocked out (using 3M stickies) area on a scale and one eye looking at the same scale marked off in large blocks of inches, i.e.' 7", 8", 10". Superimpose the images of the magnified 1 inch block over the scaled blocks (powers) of 7 or 8 or 10, whichever fits. It becomes easy to see them line up. If the magnified 1 inch block lines up with the 8" scaled block, it's 8x. I find it particularly easy when the magnified image falls in the middle of some colored sticky, showing for instance 8.5x. I can see powers down to an accuracy of about a quarter inch or 0.25x. The problem with this method is it needs to be done only at close distance, perhaps 20 feet to 50 feet at most. All binoculars increase in magnification at closer focus, so the result does not represent magnification at infinity, it represents magnification at some closer focus distance. But, since that close/infinity variation is perhaps only 2% to 3%, errors larger than that can be found easily. It takes some practice to let your eyes view two completely different images and superimpose them. I find it pretty easy to do.
OR
Measure the exit pupil as is at apparent full aperture. Record.
Assuming a 80mm binocular)
Then place a lens cap that has been cut to a 70mm aperture.
Measure the exit pupil WITH the 70mm mask. record
Then place a lens cap that has been cut to a 60mm aperture.
Measure the exit pupil WITH the 60mm mask. record
If I were using this method to test 50mm binoculars, I would test at 50mm, 45mm and 40mm.

You must measure exit pupil precisely to at least 5/100ths mm, so you need a precise dial or digital caliper. You would not be able to measure this precise with a $10 vernier caliper.
Furthermore, you must measure the mask precisely to at least one half mm.

Do the math for each aperture. The masks will show the point beyond which you have covered up all internal vignette and eliminate vignette from the equation. You need at least two measurements to agree

 

[Maljunulo]

Project the exit pupil onto a piece of tracing velum and apply the measuring device of your choice.

 

[GrampaTom]

Not an answer to the OPs specific question as this does describe equipment thats not widely available to perform...

8x32 binocular with the most 'wow!' effect

The 10x42 SE is my regular birding binocular and I know it's the thing here to wax lyrical about what one owns, but IMO some of the praise that comes for it is slightly over-romanticised due to its status as the last great porro. It's unquestionably a fine binocular and I like it very much, but...

www.birdforum.net

See #s55-62

Perhaps thats a/the point. I agree it is interesting

 

[mekidear]

Objective lens diameter divided by exit pupil diameter equals magnification. The problem is, how to measure the diameters precisely. I don't have the tools to do so. I'd like to know if there is an easy way to measure the magnification of a binocular.

I did think of this one but it is not obvious (to me) how to measure the true objective diameter. It might be restricted by its mounting or somewhere internally. Also I am not keen on operating a vernier near my lenses to measure exit pupil.

From Cloudy Night's. https://www.cloudynights.com/index.php?findpost=63263

For magnification, see Henry Link's reference to Kimmo Absetz’s method of establishing a reading for a small power monocular:
Take a reading of a tape measure at some distance (75' to 100' away) using a monocular, then take a reading of the tape through the binocular with the monocular behind the binocular eye lens. [Used a small scope to accurately get a measure on a scale about 100 feet away (reading approx 14-15 feet). Then used the small scope behind each binocular to take another reading and divided the two values.] Division of the readings gives the power. All magnifications reported here use that method. It gives a fairly accurate reading, but because of it's relatively close (100 feet in my case) distance, all readings may produce magnification that is slightly (approx 1%) high. (In any binocular, Magnification usually varies by ~2% and by as much as 3%, from the closest focus to infinity). However, anyone trying this method would see that it can be quite accurate, and it is easy to measure power to tenths. Therefore, results are reported to 1/10th. All actual calculations produced values to hundredths, but there is no way that I can be measuring with that level of accuracy, so I have not reported it. It is impractical to measure using this method much beyond 150 feet, and in fact impossible to test using this method at infinity.
OR
Place one eye to binocular viewing a one-inch blocked out (using 3M stickies) area on a scale and one eye looking at the same scale marked off in large blocks of inches, i.e.' 7", 8", 10". Superimpose the images of the magnified 1 inch block over the scaled blocks (powers) of 7 or 8 or 10, whichever fits. It becomes easy to see them line up. If the magnified 1 inch block lines up with the 8" scaled block, it's 8x. I find it particularly easy when the magnified image falls in the middle of some colored sticky, showing for instance 8.5x. I can see powers down to an accuracy of about a quarter inch or 0.25x. The problem with this method is it needs to be done only at close distance, perhaps 20 feet to 50 feet at most. All binoculars increase in magnification at closer focus, so the result does not represent magnification at infinity, it represents magnification at some closer focus distance. But, since that close/infinity variation is perhaps only 2% to 3%, errors larger than that can be found easily. It takes some practice to let your eyes view two completely different images and superimpose them. I find it pretty easy to do.
OR
Measure the exit pupil as is at apparent full aperture. Record.
Assuming a 80mm binocular)
Then place a lens cap that has been cut to a 70mm aperture.
Measure the exit pupil WITH the 70mm mask. record
Then place a lens cap that has been cut to a 60mm aperture.
Measure the exit pupil WITH the 60mm mask. record
If I were using this method to test 50mm binoculars, I would test at 50mm, 45mm and 40mm.

You must measure exit pupil precisely to at least 5/100ths mm, so you need a precise dial or digital caliper. You would not be able to measure this precise with a $10 vernier caliper.
Furthermore, you must measure the mask precisely to at least one half mm.

Do the math for each aperture. The masks will show the point beyond which you have covered up all internal vignette and eliminate vignette from the equation. You need at least two measurements to agree

It will take me a while to get my head round this lot .

First option seems the simplest - I don't have a monocular but half a binocular will do I guess You could do this at longer range using fence posts as a scale. I will try it.
Do you have to consider the field of view of the monocular, if it is wider than the binoculars you are testing, will they restrict the view through the monocular affecting the results?

 

[henry link]

I mostly use a simple method nowadays, no exact measurements of objective lens or exit pupil required. Photograph a distant object with a camera set at infinity focus, then without changing the camera's zoom or focus settings photograph the same object through the binocular at the center of its field. Download the photos and measure the object in each photo on a computer screen. That will determine the center field magnification of the area subtended by the photographed object. It's that relatively undistorted magnification of the central area of the fov that I want to know. Magnification outside that area will vary across the rest of the field according to the binocular's distortion profile.

 

[Eric_D]

Photograph a distant object with a camera set at infinity focus, then without changing the camera's zoom or focus settings photograph the same object through the binocular at the center of its field. Download the photos and measure the object in each photo on a computer screen.

Yes.
A phone will work instead of a camera.
Crop the two photos to precisely the object, in any image editing app. Save both files.
Examine file properties for width & height.
Divide the pixel counts.

I'm too lazy to go find a ruler!
I guess there are "ruler" apps to measure on-screen.