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I get triangular stars!!


algady
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Hi,

I get triangular stars shapes even when I'm imaging for few seconds only!!

I managed to do a good polar alignment and as you can see in PHD graph the lines are smooth and nice, so where is the problem?

scope: ED80 with no field flattern

Camera: nikon D90

This is 100% cropped of the center of the image (60 sec exp)

post-26075-0-90358000-1367230418_thumb.j

post-26075-0-45364800-1367230439_thumb.p

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If the scope still has the large threaded ring on the front holding the objective in place (going on memory as it seen years since I had an ED80) then slacken it off a tad.

Edited by Komet
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If the scope still has the large threaded ring on the front holding the objective in place (going on memory as it seen years since I had an ED80) then slacken it off a tad.

Thanks a lot, Do you mean I loosen that ring a bit? Is that safe? the scope is still in guarantee.

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Yes .... although seeing as though it is still under guarantee and if that image was taken without anything like a roof, tree branch or aerial in the way (as they can also cause strange things to happen) it might be an idea to send the image to the dealer and ask his advise.

Me though? I would loosen it a bit first to see if it improves.

The ST80 was very prone to this and on mine (from a long way back now though) I almost had to have the glass rattling. The ED80 will be subject to similar things and it doesn't take much to pinch the optics.

Other suggestions may also be available.

Good luck and let us know the outcome.

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That's sure to be pinched optics, as stated. I'd discuss with the supplier whether you try to loosen the cell ring or send it back, but it's no good like that. In general the colder it is the worse the problem becomes.

Olly

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  • 3 weeks later...

Hi all,

I've received my scope couple of days ago from the supplier as they took it back and fix it, I took some images last night but I think that the problem is still there, as you can see in this image the stars are not in nice round shape.

I'm using HEQ5 pro and I have very good guiding results as shown in phd graph.

Can anyone please advice me what can I do now?

Thanks in advance..

post-26075-0-33547100-1368704340_thumb.p

This is 60s sub

post-26075-0-55000000-1368704832_thumb.j

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You'll need a fairer comparison than that I feel - at the low resolution of the more recent image, the stars look OK. Can you post an image with brighter stars at the same resolution s the original image so that we can do a fairer comparison?

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You'll need a fairer comparison that that I feel - at the low resolution of the more recent image, the stars look OK. Can you post an image with brighter stars at the same resolution s the original image so that we can do a fairer comparison?

Hi and thanks for reply, this is 100% cropped of that same image (central area)

DSC_0068.tif

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That's better! The stars are still not a great shape but they are no longer showing the classic effects of 'pinching'.

I am puzzled by the diffraction spikes on the star images - is it possible that the twigs of a tree or something similar could have been in the field of view as this distortion is very reminiscent of that (errmm, I've done it and I'll bet I'm not alone!).

Are you using a focal reducer?

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That's better! The stars are still not a great shape but they are no longer showing the classic effects of 'pinching'.

I am puzzled by the diffraction spikes on the star images - is it possible that the twigs of a tree or something similar could have been in the field of view as this distortion is very reminiscent of that (errmm, I've done it and I'll bet I'm not alone!).

Are you using a focal reducer?

Hi, that diffraction spikes is very strange indeed!!

No, I can confirm that nothing was in the field of view just a clear sky, and again no, I'm not using a focal reducer.

Thanks for your time.

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I would email that crop to the supplier and ask for their thoughts as it is obviously not correct. It looks like there is an obstruction somewhere - like the edge of a roof, twig, ariel etc but if it is clear as you say then the problem must lie within the scope. Could you connect your QHY5 to the ED80, point it at a bright star (or Jupiter say) and see what comes out?

Edited by Komet
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I would email that crop to the supplier and ask for their thoughts as it is obviously not correct. It looks like there is an obstruction somewhere - like the edge of a roof, twig, ariel etc but if it is clear as you say then the problem must lie within the scope. Could you connect your QHY5 to the ED80, point it at a bright star (or Jupiter say) and see what comes out?

Yes, It is strange!! I emailed them and they are very helpful and give an excellent support.

I will take more images tonight if it is clear.

Thanks a lot

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