I have Pentax 7x50 PCF WP binocular. All bright stars look like Saturn -- i.e. they have flares on the sides -- even in the center of the field. Is this a sign of pinched optics, or something else, or normal?
Pinched Optics?
Started by hemismith, 11/20/2006 09:06PM
Posted 11/20/2006 09:06PM
Opening Post
Posted 11/21/2006 01:34AM
#1
I have Pentax 7x50 PCF WP binocular. All bright stars look like Saturn -- i.e. they have flares on the sides -- even in the center of the field. Is this a sign of pinched optics, or something else, or normal?
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Craig:
Several years ago I bought a pair of 11x80's and they acted much the same way. I was quite disappointed and thought I had purchased some bad optics....
Well, I did have some bad optics but I did not buy them, I was born with them...
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Both your 7x50s and my 11x80's produce exit pupils in excess of 7mm. What this means is that you are viewing through the entire lens of each of your eyes. The center of your eye's lens is sharpest and like most systems as you use more and more of the objective, the more aberrations pop up.
In cases like this, most often otherwise undetectable astigmatism raises it's ugly head and you are stuck with "spikes" or "flares".
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The test is to hold the binoculars steady and looking with one eye, rotate your head. If the spikes rotate as you rotate your head, then the problem is with your eye.
This is not really a problem because it only shows up in situations like this but it is annoying.
I think this is one reason for the increased popularity of high magnification binoculars, I think 10x50's are much more popular now than 7x50s. You also see more at higher magnifications.
Jon
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Craig:
Several years ago I bought a pair of 11x80's and they acted much the same way. I was quite disappointed and thought I had purchased some bad optics....
Well, I did have some bad optics but I did not buy them, I was born with them...
-----
Both your 7x50s and my 11x80's produce exit pupils in excess of 7mm. What this means is that you are viewing through the entire lens of each of your eyes. The center of your eye's lens is sharpest and like most systems as you use more and more of the objective, the more aberrations pop up.
In cases like this, most often otherwise undetectable astigmatism raises it's ugly head and you are stuck with "spikes" or "flares".
---
The test is to hold the binoculars steady and looking with one eye, rotate your head. If the spikes rotate as you rotate your head, then the problem is with your eye.
This is not really a problem because it only shows up in situations like this but it is annoying.
I think this is one reason for the increased popularity of high magnification binoculars, I think 10x50's are much more popular now than 7x50s. You also see more at higher magnifications.
Jon
Funding Member
