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Divergent/Convergent Binocular Test Wanted

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#1 Guest_**DONOTDELETE**_*

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Posted 30 March 2004 - 05:13 PM

The eye can compensate for divergent images in binos. That is normal for our vision. But I think these binos have convergent images.
Is the following the convergent/divergent test?
I put the vertical edge of a chimney in the center of the left eye binocular. Then when I open the right eye, in the right binocular, the chimney edge should be to the right of the center. In these binos, it is to the left.
Is this the divergent/convergent test for binos?

#2 EdZ

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Posted 30 March 2004 - 05:28 PM

Divergence is spread apart. Convergence is crossed over.

Your binocular shows images crossed over or convergence.

I wrote the following on these two problems in an article last year. The following is from the article.

Generally there are three collimation errors to be concerned about. For all misalignments the allowable error is smaller as magnification increases. Actually this results in the same apparent visual error, the angular error multiplied by the magnification. My actual experience is that my eyes will not allow separation as large as defined by these limits, especially at magnifications of 15x and higher.

Vertical Alignment, a serious error, is when one image is higher than the other image. The eyes have no muscles to accommodate for vertical error. The allowable divergence is only 4 arcmin at 7x to 10x, only 3 arcmin at 12x to 15x and 2 arcminutes at 15x to 20x. Personally, I cannot tollerate even 2 to 3 arcminutes of vertical error even at magnifications of 10x and only 1 arcmin at 16x.

Horizontal Convergence, the least problematic error, is when the image in the right eyepiece is to the left of the image in the left eyepiece. You might think of this as cross-eyed. The most separation can be tolerated in horizontal convergence, 10 arcmin at 7x to 10x, 8 arcmin at 12x to 15x and 6 arcmin at 15x to 20x. Most eyes can readily accommodate this error, but these limits I find a little too wide. I could not tollerate even half that much.

Horizontal Divergence, another serious error, is when the image in the right eyepiece is to the right of the image in the left eyepiece. The images are spread apart, an error that the eyes cannot accommodate without strain. The allowable error for horizontal divergence is 6 arcmin at 7x to 10x and only 4 arcmin at 12x to 15x and 3 arcmin at 15x to 20x.

Keep in mind, the magnification of your binocular has a significant influence on how you see this error. Your eyes see the apparent error, or the angular error times the magnification. For instance a 3 arcminute error in a 10x binocular will appear to have a magnified apparent size of 30 arcminutes. That same error in a 15x binocular will have an apparent size of 45 arcminutes and in a 20x binocular will appear as 60 arcminutes.

For reference 1 inch at 100 yards is just slightly less than 1 arcminute.



These tollerances can be found published in the book listed below. Personally I cannot accomodate my eyes to these tollerances. I would recommend cutting all of these in half. HD is the error I see almost all the time. Because of the way the prisms rotate, there is always some vertical alignment error with it. I can accomodate 2-3 arcmin error at 10x-12x. I begin to find it difficult to accomodate a 2 arcmin error at 15x-16x. I could not tolerate 2 arcmin error at 20x.

In large binoculars at 25x or higher, I find any collimation error of more than 1 arcminute unacceptable. At 44x, I have my BT100 merged to 30 arcsec. The BT100 at 62x cannot handle 1 arcmin of miscollimation.

Rotational Error, a fourth collimation error, is when one image is rotated in relation to the other image. I have never seen it in any binocular.

For information on how binoculars work and especially collimation, see;
J. W. Seyfried, “Choosing, Using & Repairing Binoculars”, University Optics, 1995

In Seyfried's book he clearly spells out the errors in descriptive terms in the body of the book. In the back of the book is a simple table showing the allowable errors. His tables show the limits for the various errors "exactly oppostite or reversed" to the way I have listed them here.

Upon finding this what I though to be a discrepency, I then re-read his book and determined that I clearly understood what he was describing as the more serious error. I wrote a letter to Mr. Seyfried and asked him if Convergence has the greater allowable error and Divergence has the lesser allowable error as described in the text and not as shown in the tables. He replied that is correct.

[It was pointed out to me at a later date that whether you call it convergence or divergence depends on which way you consider the light passing thru. So there may be no error at all in Seyfied's book. It may just be the way it's presented. Follow the text explanation, it's very clear.]

edz

#3 Guest_**DONOTDELETE**_*

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Posted 30 March 2004 - 05:56 PM

Any simple solutions? I don't think this brand has collimation screws. I will have to do some research. They just arrived. It is encourageing that convergence has a greater allowable error, but when you pay good money who needs the headache.


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