weird non concentric halo around main star

[philip58]

hi,
i was imaging this evening with my canon450d at prime focus through c9.25, and late in the evening i started to get a large uneven weird halo around main star. Any ideas what would cause this. It appeared on all exposure, no matter what length.
i am abit concerned that i may have done some damage to the camera as it dropped out of the telescope on to the concrete floor ( 2 foot). I thought the problem was starting to occur before then but showing more of a dull halo. I then took some normal images indoors and they seemed fine but when i fitted it back on telescope this weird halo was on the images again.
Philip

[xcoupeb]

Could it possibly be from dew on the corrector you said it was only late in the night? I had this happen to me with my camera lens set up to do a timelapse during the night, checked all the pics the next day and 95% were no good cause dew had formed on the lens

[philip58]

Hi again
Hi again,
This is my image with the halo effect. The halo is a different shape every time you do other areas of the sky. It looks pretty though!!!
The sky had a very thin layer of cloud all evening...could this be the problem. i thought the corrector plate looked ok and i had dew shield anti dew equipment fitted
I am looking forward to see what happens on the next clear night.
Thanks for responses so far
Philip

[philip58]

Hi again.
I will post some images later showing this evenings images with halo. I have tried exposures without my astronomik lpr filter taken out of the camera as well and this made no difference.

All the corrector plate did look a bit misty when a light is shone over it...there are no suspicious marks on there however. Would any slight mistiness produce the effect on my earlier images.
I dont like cleaning corrector plate as i have heard its better to leave them unless really bad. The telescope is about a year old and not used excessively and is well looked after. I would be interested to know if enthuisasts of astrophotography clean the corrector regular to produce better images.If so what would be the best way of doing this.

The corrector plate looks spotless after any mistiness clears when brought inside.
Philip

I think i may be finding the fault. The secondary mirror inside has like a misty off centre concentric smear covering about half the mirror. This shape is very similar to the halo in the images. I have took the eyepiece end off to let some air in but after 45 mins its still the same size.Any suggestions how to get rid of this.
philip59 (http://www.astronomyshed.co.uk/forum/memberlist.php?mode=viewprofile&u=2055)NebulaPosts: 9Joined: Thu Oct 27, 2011 8:31 am

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[Daveskywill]

My thought: is that it could be of course not only not concentric, but so

it's 2 circles with different radii and they're shifted. If you look to the left

and get it bold enough, you might see where the edges of the 2 rings

intersect. And it would be detectable and not a total smooth

transformation. And the inward parts too.

I'm wondering if it could be due to both and optical halo in the sky and

one of your optics. David

[Daveskywill]

I'm sorry to hear you dropped your CCD.

I'm wondering if there's a place you can take it to have it

professionally checked and calibrated.

It could be an optical window on it shifted.

Other than that, I don't know.

David

[philip58]

Hi,
Further progress I think is being made. I thought when I was discussing this problem on here, i had taken an exposure without the focal reducer and it was still bad.
Well this evening, clear skies at last!!!!, i have been working through my optic system and when i remove the focal reducer i get a perfectly clean exposure. When i replace the focal reducer the large misshapen ring is there again on the images. The focal reducer is definitely screwed in square and tight( good fit)
I am sure this cant be right to have images as bad as that with a focal reducer (Celestron f6.3)
Anyone any ideas

can a focal reducer become faulty, its not been dropped, or knocked about

thanks
Philip

[philip58]

I have been told that the probable cause of this is that the distance between camera chip and focal distance is wrong

I have a c9.25, focal reducer6.3 and canon450d.
Does anyone have this configuration and who knows the correct spacing distance between chip and focal reducer.

My distance is about 150mm and i gather thats too much
Thanks
Philip

[philip58]

Hi again.
I have not been on for awhile because of other commitments, but i feel the problem is as been mentioned,the distance between the focal reducer and camera chip, and it has been stated this should be about 100mm.
I now need two adapters, the first to connect from the Revelation Astro 2inch focuser and the celestronf6.3focal reducer and the second a 2 inch adapter from the focal reducer to the canon 450d camera.
The first adapter has to have a 2inch push in to the revelation focuser and a 2 inch female thread to the focal reducer. The second adapter has to have a 2 inch male connector to the focal reducer and a 2inch connector to the camera.
I was going to purchase the orion 05269 prime focus camera adaper for 2inch focusers from SCS Astro, and it would have unscrewed in to the 2 adapters i require, but it is no longer available now ( tsunami casualty). This is the link if you want to see an image of it.
http://www.scsastro.co.uk/catalogue/orion-prime-focus-camera-adapters.htm?term=camera+adapters.
Any help would be much appreciated where i can obtain these items. I am from UK.thanks
Philip