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Which side of the off axis guider faces the telescope

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#1 WConde

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Posted 16 May 2021 - 06:55 AM

Okay!  I am embarrassed... I disassembled my ZWO OAG and now I don’t know which side of the prism should face the telescope.  I’ve been searching the internet and I am getting conflicting  information.   Some say that the side with the glass in 45 degree angle should face the telescope and others say it should be the back of it (which is flat and has a small “circle” on it). Which one is right


Edited by WConde, 16 May 2021 - 07:18 AM.


#2 Dynan

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Posted 16 May 2021 - 07:22 AM

The 'small circle' should face the objective. Think of light reflecting at a right angle (caused by the 45° angle of the prism).

The light will enter the flat side and reflect 90° to the guide camera.

 

If all else fails, try both ways, and see if you get light up through the guide cam tube. Physics doesn't lie.


Edited by Dynan, 16 May 2021 - 01:36 PM.

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#3 rgsalinger

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Posted 16 May 2021 - 08:10 AM

If you look down from the top of an OAG, you will see something on one side - the prism is effectively just a flat mirror. That will make it easy to know which direction is the telescope side. Not that Dynan is wrong at all, just that I find it easier to just look through it and figure out which side is accepting lite. 


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#4 nemo129

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Posted 16 May 2021 - 11:34 AM

A picture is worth...well however many words you like....

 

 

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  • OAG Diagram.jpg

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#5 WConde

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Posted 16 May 2021 - 01:08 PM

A picture is worth...well however many words you like....

Thank you very much!!! I will save this one.



#6 WConde

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Posted 16 May 2021 - 01:09 PM

If you look down from the top of an OAG, you will see something on one side - the prism is effectively just a flat mirror. That will make it easy to know which direction is the telescope side. Not that Dynan is wrong at all, just that I find it easier to just look through it and figure out which side is accepting lite. 

I did as you said and confirmed what Dynan said.  Many thanks!


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