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Thread: Triangular stars

  1. #21
    pederv's Avatar
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    Default Re: Triangular stars



    Does your mirror cell have foam bumpers to help keep the primary from sliding back and forth and hitting the metal mirror cell?
    I replaced my primary a couple of years ago and the primary had a diameter a few mm larger than the old one. I tried squeazing the new primary into the mirror cell with the foam bumpers as they were. Even though the foam bumpers didn't feel like they offered any resistance they were almost fully compressed, the result was pinched optics. I pulled the foam bumpers out of the mirror cell and replaced them with a single layer of duct tape, so when the primary moved back and forth it wasn't hitting the mirror cell.
    Maybe your primary has a diameter just a little bigger than the "normal" primary mirror for your scope and you're having the same problem I had.
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    Name - Verne / Call sign - KF7UHL
    Scopes - Orion Atlas 10 EQ-G GoTo / Orion 130ST on an AstroView Mount with RA Drive
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  2. The Following 2 Users Say Thank You to pederv For This Useful Post:

    AustinPSD (11-23-2013),dj_judas21 (11-23-2013)

  3. #22
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    Default Re: Triangular stars

    Quote Originally Posted by AustinPSD View Post
    Have you tried with, and without the coma corrector?
    I only use the coma corrector with the camera, not with eyepieces. I get triangular stars with and without it
    6" f/5 GSO Newtonian, Celestron Advanced VX mount, 2" coma corrector, Canon 600D with full spectrum mod
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  4. #23
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    Default Re: Triangular stars

    Quote Originally Posted by pederv View Post
    Maybe your primary has a diameter just a little bigger than the "normal" primary mirror for your scope and you're having the same problem I had.
    I think you might be on the money. The mirror is pretty much touching the insides of the mirror clips at the edges. I'll see if I can modify the cell to avoid this pressure.
    6" f/5 GSO Newtonian, Celestron Advanced VX mount, 2" coma corrector, Canon 600D with full spectrum mod
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  5. #24
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    Default Re: Triangular stars

    So I removed the mirror cell again, and this time I checked for side pinching, as per pederv's advice. The mirror does seem to be pressing quite hard against the sides of the "pegs" and is wedged against all three (see pic). On one peg, it is wedged so tightly that it isn't even resting on the cork pads underneath! You can just about see the cork pad in the photo, and a 2mm air gap between it and the mirror. Unfortunately the pegs are metal with no rubber or fabric on them so it looks like I might have to file them back. Before I get my metal files out, is this a sensible course of action?

    I suppose this is grounds for a warranty replacement, but the telescope was mail-ordered from Germany and I don't really fancy returning it, or its mirror cell.

    mirrorclips2.JPG
    6" f/5 GSO Newtonian, Celestron Advanced VX mount, 2" coma corrector, Canon 600D with full spectrum mod
    http://www.jonathangazeley.com/category/astronomy

  6. #25
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    Default Re: Triangular stars

    I got a response from Teleskop-Service, which is pretty much what I was expecting. I'll try this later tonight and post back with my progress. I hope this information is useful to someone else who might be having the same problem.

    you are probably right - it is the sideways pressure of the mirror clips. This can be more pronounced if the temperatures get lower. The best way to deal with this problem is to take the mirror out of the cell and file/sand off a bit from the clips. You can even take off so much that you can fit a piece of felt or velours inbetween. (but this is an option not a must).
    6" f/5 GSO Newtonian, Celestron Advanced VX mount, 2" coma corrector, Canon 600D with full spectrum mod
    http://www.jonathangazeley.com/category/astronomy

  7. #26
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    Default Re: Triangular stars

    I finally found time to look at and fix the problem. It was pressure from the clips on the side of the mirror. I wrote a detailed report with photos on my website - can't be bothered to copy it here too, but if anyone is interested you can find it at Pinched optics – the cure | Jonathan Gazeley

    Thanks to everyone who advised me on diagnosing and fixing this problem - this is a great community
    pederv and OleCuss like this.
    6" f/5 GSO Newtonian, Celestron Advanced VX mount, 2" coma corrector, Canon 600D with full spectrum mod
    http://www.jonathangazeley.com/category/astronomy

  8. #27
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    Default Re: Triangular stars

    It looks like you've found your problem.
    I'm looking forward to seeing your star test results.

    Clear Skies
    Name - Verne / Call sign - KF7UHL
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  9. #28
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    Default Re: Triangular stars

    I haven't got time to get out of the city tonight but I just set up the telescope in my garden and pointed it at a bright star. Can confirm that the triangular stars have been cured! It was actually a bit strange throwing it out of focus and not getting a triangle...

    Hopefully tomorrow I can get out of town and see how it performs on DSOs.
    pederv and davidjbillo like this.
    6" f/5 GSO Newtonian, Celestron Advanced VX mount, 2" coma corrector, Canon 600D with full spectrum mod
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    Default Re: Triangular stars

    Looking forward to seeing an image.

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  11. #30
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    Default Re: Triangular stars

    So here are my images from last night. I had a friend with me so I didn't want to spend hours taking frames - we looked at a few of the brightest objects and took a few frames of each. The stacks are quite noisy as a result, but you can clearly see that the telescope's optics are working nicely.

    Thanks to everyone who helped me sort this issue out. I now have a load more questions about how to do image processing properly, but I'll start a new thread for that

    horsehead-16b.resized.jpgm31-16b.resized.jpgm42-32_pregamma_1_mantiuk06_contrast_mapping_0.1_saturation_factor_1.2_detail_factor_1b.resized.jpgm45-16b.resized.jpg
    pederv, Leveye and davidjbillo like this.
    6" f/5 GSO Newtonian, Celestron Advanced VX mount, 2" coma corrector, Canon 600D with full spectrum mod
    http://www.jonathangazeley.com/category/astronomy

 

 
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