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OAG and Filter Wheel Configuration.

Accessories Astrophotography Beginner Cassegrain Equipment Filters Imaging Meade Optics SCT
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#1 Karl S

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Posted 23 May 2024 - 08:55 AM

Brand new to astronomy, and I couldn't find this answer elsewhere. I'm trying to figure out the best way to attach my OAG and filter wheel.

 

I have an LX90 8" SCT. There is a 2" 6.3 focal reducer on the back of my scope. From there I will be attaching a 5 position filter wheel (1.25"), an off axis guider (with guide camera), and a primary camera (1.25" adapter). 

 

Trying to stick to a budget (until I determine if this hobby is for me,. I picked up a used OAG and filter wheel.

 

Here is my issue.

 

The filter wheel is 1.25" and the OAG is 2". What is the best way to connect these? It makes sense to have the filter wheel after the OAG (so it gives the brightest image for guiding) but as I understand it the distance from the center of the off axis guider to the sensor of both cameras needs to be the same. Does that mean I just need to attach an extension tube to the 1.25 guider tube to account for the added length of the filter on the primary camera?

 

Oh ya, I also have to use a 90° mirror because the LX90 has such poor clearance between the scope and base. Right now I have a 2" to 1.25" mirror (came with scope).

 

Does my question make sense?


Edited by Karl S, 23 May 2024 - 08:56 AM.


#2 jmillsbss

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Posted 23 May 2024 - 09:27 AM

Brand new to astronomy, and I couldn't find this answer elsewhere. I'm trying to figure out the best way to attach my OAG and filter wheel.

 

I have an LX90 8" SCT. There is a 2" 6.3 focal reducer on the back of my scope. From there I will be attaching a 5 position filter wheel (1.25"), an off axis guider (with guide camera), and a primary camera (1.25" adapter). 

 

Trying to stick to a budget (until I determine if this hobby is for me,. I picked up a used OAG and filter wheel.

 

Here is my issue.

 

The filter wheel is 1.25" and the OAG is 2". What is the best way to connect these? It makes sense to have the filter wheel after the OAG (so it gives the brightest image for guiding) but as I understand it the distance from the center of the off axis guider to the sensor of both cameras needs to be the same. Does that mean I just need to attach an extension tube to the 1.25 guider tube to account for the added length of the filter on the primary camera?

 

Oh ya, I also have to use a 90° mirror because the LX90 has such poor clearance between the scope and base. Right now I have a 2" to 1.25" mirror (came with scope).

 

Does my question make sense?

Sorta.

 

You've really got a long SERIES of questions.  And questions always beget questions in this deal!   You may have to sort through a few replies to get them all answered.  That clearance issue is always gonna be a hassle for you.  AP from an AltAz mount is a limited setup.  I'm wondering if you shouldn't ditch the FW for now and just use a filter slide or even see if your OAG will accept filters? The filter wheel is REALLY gonna limit your access to the zenith, where the sky is darkest.  You didn't say what cam you're using?

 

Let me go back.  You're using the 0.63x reducer/flattener, and you should.  Unless you're doing planetary and lunar, f/10 is too slow.  BUT - My C8, when using the .63x FR/FF, requires 105mm of back focus to achieve best full field correction.  With the AltAz mount, you'll never get there.  It doesn't have to be the full 105, and various people will say various things about the backfocus being 55-105mm.  I'm using about 70mm right now and just barely cropping the outer 10% to discard wonky stars.

 

A lot of stuff to consider, but first, what camera are you using?



#3 Karl S

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Posted 23 May 2024 - 09:44 AM

My primary camera is an ASI585MC.

#4 Karl S

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Posted 23 May 2024 - 09:45 AM

I also forgot to mention my scope is mounted on an EQ wedge.


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