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Jammy

Strange Diffraction Spikes

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Does anyone know what the strange diffraction spikes are in this image?  I know the star Alnitak is pretty bright but wasn't expecting this.

I've never seen this happen before.  Is it an SCT thing, or a MY SCT thing?

I've seen straight diffraction spikes, but never curved.

Is there anything I can do to stop this?  Could it be a collimation issue?  I did check before I started imaging, but thought everything looked ok.

My scope is a Celestron C9.25 XLT, and I'm using a f/6.3 corrector/reducer with modded Canon EOS 600D.

Thanks in advance :)

IC434 second try.jpg

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Not a collimation issue judging by the other star shapes. Most likely a reflection from something internal or external.   :icon_biggrin:

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32 minutes ago, Jammy said:

Is there anything I can do to stop this?

Frame the picture differently. This is a lens flare, surely taking place inside the reducer. Bright stars are bound to cause this effect at certain angles, but especially near the edge of the lenses. It's the first time I see such a long flare, though. Do not discard the pic, everything unusual is interesting, and it might prove artistic when you look at it with an open mind. The flare frames the Horsehead pretty well.

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Thanks guys.  I did wonder if it was from the focal reducer.  I've never seen a flare this long either, thats what made me ask.

I did try to move the star out of shot, but then struggled to find a guide star in the OAG.  I might have done better moving it into the middle.

Next time I'm out I'll try imaging a bright star, central in the frame, to see if there is any flaring.

As you say, keep an open mind.  I'll try processing it again and see if I can extract some detail :)

Edited by Jammy
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That's a great example of the effect.

Altinak is probably the star that causes more weird effects than any other!

Mark

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On 12/21/2017 at 10:27, newbie alert said:

Did you clean the reducer beforehand? I get this on my sct sometimes..

No I didn't.  Should I clean it, and what with?  I try to touch these things as little as possible.  It looks clean when you hold it to the light and look through.

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Like I say I get this now and then with my sct and reducer...cant pin it down to after it's been cleaned as it's not every time..

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On 12/21/2017 at 14:06, sharkmelley said:

It could be internal reflections inside the baffle tube:

https://www.cloudynights.com/topic/565539-strange-arcs-of-light/?p=7688737

Mark

That's ineresting.  Have you ever had any problems like this with your SCT Mark?

I'm wondering where the reflections can be coming from.  Possibly the secondary housing?  I'm not entirely sure how to check, or if I want to.  I don't really want to start dismantling the scope.

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Id bet it's a internal reflection from the reducer..seen them on a couple of others images and the common denominator is the 6.3 reducer..i try to find an image of mine,unless I've deleted them already..

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I'm thinking its down to the reducer.  Unfortunately I don't think Celestron put as much effort into this reducer as they should have done.

Would a different brand f/6.3 reducer work with my C9.25?  I'm thinking they're probably all the same with a different brand name on the box.  

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Try flocking paper in the baffle tube. Roll it up, slide it in. It will probably stay put  by itself (without glue) when it unrolls itself. A thin material is best.

If it solves the problem you may consider fixing it more permanently.

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11 hours ago, Jammy said:

That's ineresting.  Have you ever had any problems like this with your SCT Mark?

I'm wondering where the reflections can be coming from.  Possibly the secondary housing?  I'm not entirely sure how to check, or if I want to.  I don't really want to start dismantling the scope.

No I haven't seen this with my SCT but it's a long time since it has seen active service except for planetary work.  To be honest I can't really visualise exactly how this effect is caused, however I think it is significant that this "reflection" passes through the star.  I have often seen these artifacts when the star is outside the field of view, when  the star's cone of light will be reflecting off various optical components.  But for a star within the field of view, the cone of light should not be hitting anything en route to the sensor. 

I will set up an experiment sometime after Christmas to see if I can make it happen.

Mark

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