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Celestron Focal Reducer Artifact: Solutions?

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#1 jerryyyyy

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Posted 03 February 2013 - 10:46 AM

I have my new camera working well but wanted to now use my focal reducer to get a wider FOV and to facilitate guiding. So with the help of a friend I put it on last night and focused it nicely, then took a series of targets to test how it was working. Well, among the other limitations of this approach I get this nasty eliptical artifact. I saw this in the past when I did DSLR images and also used the reducer.
Is there any hope for this. I put the plate solve in so you could see the sources of the two (there is actually a second duller one in the lower right). :tonofbricks:

The image is 600s of H-alpha, so you could cut that down, but with the obvious downsides of less signal.

Hopeless? Better brand/type of reducer?

For the record (and Google Search the backfocus from the end of the Celestron Focal Reducer to the front plate of the STT 8300M is 4 inches- 10cm).

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#2 Tapio

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Posted 03 February 2013 - 11:05 AM

I guess that's a reflection of nearby Alnitak.
It could be be focal reducer, Ha filter or something else in the optical train.

#3 SANDRO78

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Posted 03 February 2013 - 11:19 AM

Hy Jerry
As said it Tapio it shall result from the reducteur caused by the star Alnitak ,sure is 99 %!

Bye @lex

#4 jerryyyyy

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Posted 04 February 2013 - 09:45 AM

I agree it is the star... but is the only solution to stay away from the bright stuff with the reducer? I guess. Do not have this problem with the C8 alone.

#5 Rick J

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Posted 04 February 2013 - 04:11 PM

Whenever you introduce an additional optical element you increase the likelihood of such reflections. This looks like it might be coming from the star hitting the edge of the reducer. Often moving the field a minute of arc one way or the other will completely eliminate edge reflections.

Rick

#6 jerryyyyy

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Posted 05 February 2013 - 01:07 AM

Thanks, will try to move it a bit. Both bright objects are just off the edge of the reducer. Not having this problem with other objects in the Center of the image...

#7 Alex McConahay

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Posted 05 February 2013 - 12:14 PM

I once did a test of four different F 6.3 focal reducers on my C9.25. Some old, some new. Some Meade, some Celestron. All exhibited the same. This is after doing all I could do to find and mask any possible internal reflections in the tube itself. This is why I do not use my focal reducer in bright star fields.

Alex

#8 jerryyyyy

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Posted 05 February 2013 - 04:55 PM

Between a rock and a hard place on this one. At least the solution is not a more expensive reducer....






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