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    Default strange stars



    Hi Everybody

    Who met star shape I met?
    My telescope is a Megrez 120/900, with ATIK-383+L mono outside temperature was ~ -13, ÷ -17°C. ( 57.2°F average) photo. Camera was cooled -20°C below ambient. Nothing was in front of the tube. The spikes (leaves? redface1 are on all the photos, made in timeframe between 19.00 evening and 0040 morning, with all kind of narrowband filters, and did not change their angular layout compared the picture axes, as the time passed. I used a dew heater strap on an intermediate power belonging to this diameter.
    Flat pictures did not show me any special shades.ngc2244 reszlet techn.jpg


    Attached part of a 1 x 15 min bin 1x1 Ha photo

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    Default Re: strange stars

    Hello. Sure looks like a Bhatinov mask pattern. If not, I will leave it up to some of the more experienced DSO photographers to solve. I'm still at the beginners level but know how easy it is to leave the mask on and start shooting.
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    Default Re: strange stars

    Thanks for answering,
    No, mask was taken off. I realised the strange shape right in the beginning, and started the fight it varying the guiding parameters whole night, but the shape remained the same. Sorry for wrong temp conversion above, the correct temp was ~ -13, ÷ -17°C. ( 6°F average).
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    Default Re: strange stars

    Possibly a thermal disequilibrium problem? My Rumak Mak Cass shows a threefold rather than your fivefold symmetric distortion when out of balance thermally.
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    Default Re: strange stars

    Nice scope!

    Pinched optics?
    Bryan
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    Default Re: strange stars

    Quote Originally Posted by bladekeeper View Post
    Nice scope!

    Pinched optics?
    Could be. If there are bits of foil spacing in the lens cell (a common enough practice) the pinching could be due to a thermal stress. I assumed that perfectly round stars had been seen in the scope and that the combo of heating strips and low temperatures was causing a temporary pinch due to the thermal issues.

    With cooling on the detector one might need to consider a pinched window on the camera as well due to the thermals.....

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    Default Re: strange stars

    When you see something like this from temperature changes it is usually over-tightened optics with misaligned spacers and from that they are getting slightly deformed as metal contracts and expands. You can try taking the cell apart and re-seating everything and then gently and evenly tightening the lens cell down again with a good spanner tool..If your not comfortable doing this maybe send it back to Williams Optics to have it done?
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    Default Re: strange stars

    Definitely looks like pinched optics, and as nFA said the camera is probably contributing also as it shows more than the normal 3 spikes.
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    Default Re: strange stars

    Quote Originally Posted by Gabby76 View Post
    Definitely looks like pinched optics, and as nFA said the camera is probably contributing also as it shows more than the normal 3 spikes.
    Yes, if the assumption that the objective has been behaving up to now, then the quickest cheapest path to a solution is to rule out other elements of the optic train. On a cold night cooling the camera by -20C looks interesting as the first thing to check.
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    Default Re: strange stars

    Maybe... the thermal stress is a black hole for me.

 

 
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