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Thread: Diamond shaped stars

  1. #1
    gcnadam2906's Avatar
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    Default Diamond shaped stars



    Ive been noticing that some of the brighter stars will have an elongated diamond shape to them. Planets look find and dim stars look ok also. I check my collimation every time i take it out, except for the position of the secondary mirror.

    Now that being said i do have a slight astigmatism and sometimes the stars will look perfect. So is this just my eye sight, or does this sound like something is wrong with my setup. I do notice that when the laser shoots back into the laser collimator instead of it being a dot it is more of an elongated oval/ line.

    I was also wondering if anyone knows of a post that shows actual pictures of stars in a telescope that has different colimation problems, and explainations with each photo with what is wrong?

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    Default Re: Diamond shaped stars

    I don't think it is collimation it is perfectly normal. You are actually seeing the diffraction spikes. Bright stars will do that.

    Your vision must be better than you give yourself credit for
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    Default Re: Diamond shaped stars

    Ok thanks! I wasnt sure because when I see the diamonds they usually are kind of stretched out a little so I was worried.

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    Default Re: Diamond shaped stars

    An article that you might find useful, with pictures, is this one: http://www.backyardastronomy.com/Bac...0A-Testing.pdf
    Have you tried turning your head when you see the "stretched out" stars? If the stretched bit turns with you then it is most likely your eyes causing the problem. Do you observe with your glasses on?

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    Default Re: Diamond shaped stars

    Have you checked the three holders preventing the primary mirror to fall, in the unlikely event you turn the OTA upside down ?

    There should be some space (the width of a credit card) between them and the surface of the mirror, otherwise the mirror could be slightly deformed...(excuse my English, but I hope this is clear..)
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    Default Re: Diamond shaped stars

    Quote Originally Posted by PHIL53 View Post
    Have you checked the three holders preventing the primary mirror to fall, in the unlikely event you turn the OTA upside down ?

    There should be some space (the width of a credit card) between them and the surface of the mirror, otherwise the mirror could be slightly deformed...(excuse my English, but I hope this is clear..)
    We call that "pinched optics" here in the states. Could definitely be the cause.
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    Default Re: Diamond shaped stars

    Everything said so far including your astigmatism may be a possibility. My eyes have a similar problem. Without my glasses everything is one big blur ( I wear tri-focals). At night with my glasses off, if I look at the street lamp next door, with only my left eye it is round. However, with only my right eye, it's sorta triangularish!

    Good luck!
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    Default Re: Diamond shaped stars

    To check the possibility of astigmatism just take a picture at high ISO or use live view.

    The bounced-back laser beam will be elongated because the bulls eye is positioned at 45 degrees. I noticed that when the batteries run out the image of my Z12 collimator becomes elongated. Maybe that is part of the reason.

    If you have a laser collimator, why do you say you never check the secondary? All it takes is to look into the scope and see if it hits the center of the donut.

    For an expert article on the effects of collimation errors on viewing and star tests, see Thierry Legault - The collimation
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    Default Re: Diamond shaped stars

    unfortunately no scope that I know of will correct for astigmatism so you have to keep them speck on, you will have to spend a bit more on better eyepieces but we don't know what scope you have nor what eyepiece you are using so difficult to help
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