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Focus with ASI1600MM on Orion 8" Astrograph

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#1 Aryeh95

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Posted 17 July 2017 - 09:12 AM

I just got an asi1600mm on the classifieds amd yesterday I went out and tried to use it with my Orion 8" Newtonian Astrograph and I couldn't see any stars so I pointed the scope at a light and I saw huge spider veins so I extended the focus all the way out and it got smaller and smaller but it was wasn't enough even the focuser tube all the way out. So I'm assuming I need some sort of extension tube but I just wanted to confirm before I go ahead and order one. (I'm using the Baader MPCC Mark iii coma corrector and so far I've only focused with full frame dslr/mirrorless)

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#2 Rudeviewer

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Posted 17 July 2017 - 09:35 AM

In order to achieve focus on my 8" Orion, I either had to use an extension, which was not really a good option with the stock focuser, or move the primary mirror closer to the secondary.  I chose to cut my tube down and move the primary mirror in like an inch and that gave me the ability to focus with my ccd.  With a little bit of time and good measuring this took maybe a few hours tops, and after i was done is not even noticable. 



#3 bobzeq25

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Posted 17 July 2017 - 09:45 AM

I just got an asi1600mm on the classifieds amd yesterday I went out and tried to use it with my Orion 8" Newtonian Astrograph and I couldn't see any stars so I pointed the scope at a light and I saw huge spider veins so I extended the focus all the way out and it got smaller and smaller but it was wasn't enough even the focuser tube all the way out. So I'm assuming I need some sort of extension tube but I just wanted to confirm before I go ahead and order one. (I'm using the Baader MPCC Mark iii coma corrector and so far I've only focused with full frame dslr/mirrorless)

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When you pointed the scope at a light, was it at all close (like less than 1/4 mile)?  If so, you got an unrealistic picture of how much extension you need.  The Moon is a better test.

 

Moving the mirror up, as suggested above, would require an even longer extension.  It's a trick to make Newts designed for visual useful for imaging.

 

Bottom line.  Extensions are frequently needed in imaging, and figuring out how long you need, just part of the business.  If you can come to focus with a DSLR (requires 55mm of "backfocus"), the 1600 (6.5mm of backfocus, plus any adaptors used) will require an extension about 50mm long minus the optical length of the adaptors.


Edited by bobzeq25, 17 July 2017 - 09:50 AM.


#4 Aryeh95

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Posted 17 July 2017 - 10:12 AM

I just got an asi1600mm on the classifieds amd yesterday I went out and tried to use it with my Orion 8" Newtonian Astrograph and I couldn't see any stars so I pointed the scope at a light and I saw huge spider veins so I extended the focus all the way out and it got smaller and smaller but it was wasn't enough even the focuser tube all the way out. So I'm assuming I need some sort of extension tube but I just wanted to confirm before I go ahead and order one. (I'm using the Baader MPCC Mark iii coma corrector and so far I've only focused with full frame dslr/mirrorless)

Sent from my Nexus 6P using Tapatalk

When you pointed the scope at a light, was it at all close (like less than 1/4 mile)? If so, you got an unrealistic picture of how much extension you need. The Moon is a better test.

Moving the mirror up, as suggested above, would require an even longer extension. It's a trick to make Newts designed for visual useful for imaging.

Bottom line. Extensions are frequently needed in imaging, and figuring out how long you need, just part of the business. If you can come to focus with a DSLR (requires 55mm of "backfocus"), the 1600 (6.5mm of backfocus, plus any adaptors used) will require an extension about 50mm long minus the optical length of the adaptors.
I'll try that.

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