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16" Meade LX850 f8 weird glares

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#1 Joe Bruessow

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Posted 20 July 2021 - 01:02 PM

I purchased a 16" LX850 ota from a fellow CN'er in April.  The ota is mounted on a "classic" Paramount ME in a small roll-off in my back yard.  I took an EAA test shot of M51 and was very impressed by the resolution but when I took images with bright stars in the field or just outside of the field I get strange/ bright flares and glares around the stars.

 

I have just begun trying to track down the source of the glares:

 

So, this morning I went out back and made a cursory observation down the focuser drawtube with the OTA uncovered (in the daylight).  I was very surprised at the fact that I could easily see a prominant ring of light around the secondary baffle.  It was as if the secondary mirror baffle was too short (The f8 LX850's have very short baffle tubes that the primary rides on as it is)

 

Since I still have my 14" LX850 I decided to compare the baffles - just as I remembered the 14" baffle is much longer... and I can see no ring of light around the secondary mirror baffle when looking down the draw tube.  To be sure that something wasn't missing, I did a quick web search of the the Meade otas and images of the 16" vs smaller otas do indeed show a shorter baffle tube.  

 

I have attached an image of the view down the draw tube of the 16 as well as images of the 16" & 14" secondary baffle tubes.  I am certainly not an expert in this field, but this seems very odd.  Any expertise/ enlightenment is much appreciated.

 

16 inch Secondary baffle.jpg

16 inch LX850 Secondary Baffle.jpg

14 inch secondary baffle.jpg


Edited by Joe Bruessow, 20 July 2021 - 03:54 PM.


#2 Mike G.

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Posted 20 July 2021 - 01:10 PM

make a small mask that fits over the secondary housing from the outside so that it blocks light that might be entering and creating the ring.  then test.  if the glare is gone, you found the culprit.  if not, look somewhere else.


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#3 Joe Bruessow

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Posted 20 July 2021 - 01:27 PM

Thanks Mike smile.gif That is a simple test.  I will definitely try it.  I am curious if others have experienced the same issue (although I see very few people with these posting).



#4 skybsd

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Posted 20 July 2021 - 01:54 PM

I read your initial post and immediately thought of this that I came across in the past.., 

 

skybsd 


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#5 Joe Bruessow

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Posted 20 July 2021 - 01:58 PM

skybsd,

 

Thank you for the reply.  That is what I was thinking I would have to do initially... add some flat black or flocking somewhere (and maybe I do), but I want to address what I think is inadequate baffling first.  I'll keep you posted.



#6 carolinaskies

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Posted 20 July 2021 - 02:54 PM

Question... are you using a light/dew shield extending forward of the corrector plate. 

Before blaming interior baffling woes always start with exterior stray light on anything with a front glass.   

If the shield removes the annoyance you've discovered the issue.  


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#7 Joe Bruessow

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Posted 20 July 2021 - 03:05 PM

Question... are you using a light/dew shield extending forward of the corrector plate. 

Before blaming interior baffling woes always start with exterior stray light on anything with a front glass.   

If the shield removes the annoyance you've discovered the issue.  

Thanks for idea Carolina Skies.  I have a dew shield... and the issue has occured with and without the dew shield.  I will try and compare views with and without it though to see how much it is reducing to the effect.



#8 Mike G.

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Posted 20 July 2021 - 03:18 PM

Question... are you using a light/dew shield extending forward of the corrector plate. 

Before blaming interior baffling woes always start with exterior stray light on anything with a front glass.   

If the shield removes the annoyance you've discovered the issue.  

+1.  it has been one of the mysteries of the Universe to me why SCTs and MAKs do not come with dew shields.  they're quite necessary, even if you don't have a dew problem.


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#9 carolinaskies

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Posted 20 July 2021 - 04:36 PM

I know I had glares when I didn't use a shield on my F/6.3 8" LX200 and it doesn't have a long 

 

Thanks for idea Carolina Skies.  I have a dew shield... and the issue has occured with and without the dew shield.  I will try and compare views with and without it though to see how much it is reducing to the effect.

How long does the dew shield extend in front of the corrector? 
A dew shield length needs to be about 1.5x the diameter of the OTA. 
If it's too much shorter it will not be very effective.   

The other possibility is to check your EAA gear and rear cell and how it matches up differently on the 16" vs your 14".  The 16" has a  much larger flange adapter than the smaller SCTs and it's possible you are seeing a reflection that is rebounding off some component.    

My 16" F/10 rear opening is significantly larger than my 10" SCT, something I noticed immediately.  

BTW, daylight checks can play tricks on you as the amount of light is so great compared to night starlight that you may see things you think are problems when they really aren't.  



#10 kennyrichmond

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Posted 20 July 2021 - 06:50 PM

Joe,

 

See Post #84 in this thread: https://www.cloudyni...hl=meade 16 acf

 

If the photograph in my post illustrates what you are seeing, a replaced secondary corrected it. There was a tiny chip in it.

 

Ken



#11 Joe Bruessow

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Posted 02 August 2021 - 10:44 AM

Okay, it has taken a while for weather and my free time to cooperate, but I had some time last night to devote to further inspection.  Again, it is not a stray light/ dew shield issue.  It is an internal reflection of some sort.

 

Mike G. - I did 3d print a mask that extends out around the secondary adding roughly another 20cm to its diameter.  It didn't seem to make much (if any difference).  

 

kennyrichmond - I didn't read your above post carefully anough (I didn't register that post #84 in the thread you referenced was a chip issue).  I did remove the corrector and inspected the secondary.  All appears normal... Maybe one spec of dust on the secondary.

 

It just looks like an internal reflection that I can't seem to track down... but could also less likely be a thermal issue caused by cranking up my dew heater to full power (dew is a problem in my area in the summer).  I have thought about doing the "reflectix" themal blanket, but I am looking for something more obvious.

 

Attached is an EAA capture showing the flaring around the brighter stars.  

 

Attached Thumbnails

  • Elephant trunk CN.jpg

Edited by Joe Bruessow, 02 August 2021 - 11:30 AM.


#12 OrionSword

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Posted 02 August 2021 - 05:00 PM

Have you swapped out cameras to see if the effect remains?



#13 Joe Bruessow

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Posted 02 August 2021 - 05:07 PM

Have you swapped out cameras to see if the effect remains?

Yes, I have swapped cameras and the observe same effect.  

 

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