Telescope Reviews: MEASURING / TESTING Optical Aspects of Binoculars

This first link is to one post that gathered a bunch of links as help to others who want to review the types of tests they can do to measure the performance of their binoculars. So go to this post and you will find about a dozen links to other posts, mostly here in the "Best Of" threads, on how to measure various aspects of binoculars.
Links for Aspects to measure as posted in the thread "Writing a Binocular Review"

Calculating TFOV

EdZ's list of sky distances for measuring True Field of View in binoculars
How To Measure TFOV Of Binoculars

Image Sharpness Across the Field of View
Another more 'full length' discussion of Filed Sharpness discussing a method how to measure accurately so binoculars can be compared.

Measuring True Sharp Field of View

Measuring the Magnification of your binoculars
Measuring the size of an exit pupil

Measuring magnification by observing a standard scale

Measuring Aperture by three methods
observing a scale in the exit pupil directly using a loupe
checking magnification then checking exit pupil
measuring projected image of a leaser thru the objective

and more on measuring aperture
checking aperture by using masks and checking exit pupil

Things to Watch Out for when measuring magnification

Excerpts from posts on explanations of how to measure magnification:

For magnification, see Henry Link's (or Kimmo Absetz’s, or (sorry) whomever it is credited to) method of, establishing a reading for a small power monocular, reading a tape measure at some distance using the monocular, then reading the tape thru the binocular with the monocular. [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 (100feet in my case) distance, all readings may produce magnification that is slightly (approx 1%) high. (In any binocular, Magnification varies usually by ~2% and by as much as 3%, from 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 hundreths, 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 the 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, ie.' 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. 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 apereture. Record.

Assuming an 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.
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.

How To Measure the Focal Length of Binoculars
Formulas you need to know and assumptions you can make if you want to estimate the focal length of your binoculars.
You must take into consideration the refractive index of the prisms.

Here's a simple test to compare Coatings from one model to another
Look for reflections in the coatings

See the "Best Of" post on coatings for much more.

Testing Edge Sharpness by observing double stars with known separations
Oberwerk BT100 - Stock 24.5mm ep sharpness
and Barry Simon tells us how he tests for edge distortions and Field of View in
Pop quiz: 22x100 Obe's or 20x77 Miyauchis

Deciding when it is necessary to adjust the collimation
Collimation

Measuring Eye Relief
and determining the difference between measured eye relief and usable eye relief

Exit Pupil, Brightness and AFOV
Does AFOV affect the brightness of the image in the exit Pupil?
How to test the Illumination of the Exit Pupil

Brightness in the Exit Pupil

and please excuse that I borrow this from another forum but here is an excellent discussion on
Thoughts on exit pupil, brightness, and resolution
it actually discusses the measuring of brightness in the exit pupil

Edited by EdZ (05/17/08 01:07 PM)

Post Extras