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Celestron 8SE secondary mirror crack?

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#1 DanBorja

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Posted 11 June 2021 - 09:20 AM

Hi all,

 

I got a friend who just recently purchased an 8" SCT (took 8 months to get one because of low availability) and this morning he came over to test it for the first time and image Jupiter and Saturn. So, after aligning, as I was focusing on Jupiter I noticed a strange pattern on it's moons. Instead of the usual out of focus donut pattern, I saw what it looked like an "ON/OFF" symbol, basically a circle with a vertical line on the upper part. Did a test stack on Saturn and the image showed double limbs all over the planet.

 

I'm thinking the secondary mirror has a crack since nothing else looks damaged and there wasn't anything strange on the imaging train. We switched to my 6"SCT and we didn't have any issues at all, perfect donut pattern, no double limbs, achieved good focus.

 

Does anybody have an idea of what is going on with the optics?

 

PAA21CX.png

f0durAe.png

 



#2 WarmWeatherGuy

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Posted 11 June 2021 - 09:41 AM

Had the scope fully cooled down?



#3 DanBorja

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Posted 11 June 2021 - 10:13 AM

Yes, it was out for at least an hour and a half, the seeing was really good and I got really good images through my 6"sct. This is nothing I've deen before with my scope, so I don't think this was caused by internal heat.

#4 jmiller1001

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Posted 11 June 2021 - 10:29 AM

I'd have to imagine that if you remove the rear cell cover and examine the secondary through the rear visual port, you should be able to see any visible damage to the secondary mirror.



#5 Eye stein

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Posted 11 June 2021 - 10:57 AM

I would try collimating it first since the colors are all over the place....red focuses before green etc...good luck

JL


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#6 rmollise

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Posted 11 June 2021 - 01:28 PM

A crack in the secondary would be VERY unlikely to be the culprit. 

 

Main suspects:

 

Scope has not acclimated to outdoor temps.

 

Seeing.



#7 wizzlebippi

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Posted 11 June 2021 - 01:42 PM

I've seen things like that if a neighbor has a light on and it's on axis enough to show up as a weird reflection. A dew shield does wonders for blocking stray light.

Also, if you really want to, you can pull the secondary on a fastar equipped 8SE and take a look. The secondary is indexed so you won't even mess up the collimation.
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#8 alphatripleplus

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Posted 12 June 2021 - 06:41 AM

What altitude were Jupiter and Saturn at when you noticed the issue?



#9 jgraham

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Posted 12 June 2021 - 06:46 AM

The vertical line sounds like a textbook description of a thermal plume rising off of the baffle. This suggests that acclimation is the culprit.

#10 Old Speckled Hen

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Posted 12 June 2021 - 08:45 AM

Gotta go with the flow here..

 

Also, if you really want to, you can pull the secondary on a fastar equipped 8SE and take a look. The secondary is indexed so you won't even mess up the collimation.

True, hadn't thought of that.  At the same time have a looksee at how the mirror is tilted in the holder.. ..whistling.gif

 

Please get back to us and let us know how you get on.


Edited by Andrew Brown, 12 June 2021 - 08:50 AM.


#11 DanBorja

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Posted 12 June 2021 - 12:22 PM

Thank you all for all of your answers. I'm going to do a trouble shooting session with more time and will get back to you.

 

I'll make sure to acclimate the tube for at least two hours prior and check if the issue persists, if it does, I'll check for collimation and will take a look at the secondary mirror too see if there's any signs of damage.

 

Clear skies!




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