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Blue halo 6.3 SCT

collimation dslr Meade observing
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#1 woody wood

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Posted 22 February 2020 - 09:27 PM

These images were taken using my Meade SSC 6.3 Schmidt Cassegrain telescope. For some reason there is a very strong blue halo effect happening. I’ve never seen this before through an F/10 SCT but is this a common occurrence in a 6.3 scope? This happened while pointing at very bright Venus in the western sky. When I slewed over to Sirius the halo was less pronounced I then went over to the Orion Nebula and it was nonexistent to my eye. All of what I saw was 3 through a26 mm Plössl eyepiece. I then took a couple of snapshots using my DSLR. 

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#2 woody wood

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Posted 22 February 2020 - 09:32 PM

More shots

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#3 jgraham

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Posted 22 February 2020 - 11:27 PM

Hmmmm, I haven't noticed in any of my f/6.3s, but I was looking at Venus this evening with my 8" f/10 LX80 and I did see the blue halo. Kinda purdy. I just figgered that it is a reflection or diffraction from the secondary baffle.


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#4 carolinaskies

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Posted 23 February 2020 - 06:49 AM

Atmospheric diffraction. Venus is notorious for this due to low height. Add in a lot of moisture in our own atmosphere and blue violet prismatic effect becomes quite apparent. Note you are seeing it on the brightest objects in the sky at low altitudes, not on ones straight overhead.

Especially in the northern hemisphere this winter which has been laden with a lot of moisture.
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#5 Jon Isaacs

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Posted 23 February 2020 - 07:45 AM

Atmospheric diffraction. Venus is notorious for this due to low height. Add in a lot of moisture in our own atmosphere and blue violet prismatic effect becomes quite apparent. Note you are seeing it on the brightest objects in the sky at low altitudes, not on ones straight overhead.

Especially in the northern hemisphere this winter which has been laden with a lot of moisture.

Atmospheric diffraction is asymmetric with blue/violet on one edge and red/orange on the other.  This is an example of atmospheric diffraction of the crescent Venus about 10% illuminated.  In its current phase, Venus is smaller but the same effect will be there.

 

3912358-Venus Through the Eyepiece.jpg
 
Jon

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#6 woody wood

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Posted 24 February 2020 - 08:29 AM

I had read somewhere on this forum that flocking the tube will greatly reduce if not eliminate this halo problem. I was just amazed at how pronounced that blue ring was. Wondering if this is an inherent issue with the Meade 6.3 wide-field SCTs. All things considered be it atmospheric or position in the sky as well as flocking together may result in a combination of magic bullets. 


Edited by woody wood, 24 February 2020 - 08:38 AM.


#7 bbqediguana

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Posted 24 February 2020 - 09:19 AM

I had read somewhere on this forum that flocking the tube will greatly reduce if not eliminate this halo problem. I was just amazed at how pronounced that blue ring was. Wondering if this is an inherent issue with the Meade 6.3 wide-field SCTs. All things considered be it atmospheric or position in the sky as well as flocking together may result in a combination of magic bullets. 

Very interesting! I was out last night and saw the same thing on Venus. I first swapped out the eyepiece - same thing. Then I removed my star diagonal - same thing. Next I said out loud "I guess I should try flocking this thing!". LOL!

 

For the record, I have a Meade f/10 8" SCT - so I presume the halo is from moisture or maybe even ice crystals high in the atmosphere and it was just showing on low placed, bright objects like Venus and Sirius.

 

Cheers!

 

Rick



#8 luxo II

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Posted 24 February 2020 - 07:27 PM

There’s no point flocking or blackening anything until you have identified the source of scattered light - one thing it almost certainly ISNT is the inside walls of the OTA.

IMHO the cause is more likely scattering or internal reflection somewhere in your optics - anywhere between the corrector and the eyelens of the eyepiece.

It could also be light scattered at a grazing angle off a metal surface - possibly the exterior of the central baffle, or the secondary mirror baffle if that is shiny.

Ice crystals produce scattering at specific angles (tens of degrees) not a narrow angle like this.
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