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Image train and backfocus

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#1 Subspace

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Posted 04 October 2022 - 10:56 AM

Hell CN,

 

I just ordered ASI585MC and had a question on how to attach it to C6 for correct back focus. This is my 1st telescope I received 2 weeks ago: C6 with SW SAGTI.  I heard on forums we can multiply 5x or 7x to 2.9um pixel (ASI585mc) to get the ideal F ratio for the camera (7 x 2.9 = 20.3). Since its an F10 scope - planning on using my Barlow 2x to make it F20 which is close to the camera's 20.3 F ratio? 

 

For image train, should I attach 2x barlow directly to back of C6, then 1.25 nose piece to barlow, then camera to nose piece?

 

Edited: Addendum after 1st reply:

 

FAQ shows: Eyepiece adapter ---> (focuser) ---> filter ---> (ADC) ---> Barlow ---> camera.

 

What is a "focuser"? FAQ does not elaborate. Do I need one or can I manually focus using the focus knob?

-I see these online: EAF or Helical focuser. I am not using auto guiding yet. I will be will using the built in tracking that comes with synscan wifi mount. Can you provide me with a link on what kind of focuser I need? 

 

Also the FAQ mentions "Eyepiece adapter". Is this the same as 1.25 Nosepiece that comes with the camera?

 

Also if I increase the barlow to 3x, then Jupiter will be more than 200 pixels? Does the image degrade due to oversampling since I am much higher than the recommended f ratio for the camera's 2.9 um?

 

Thank you

 

 

 

EN-ASI585MC_143.jpg


Edited by Subspace, 04 October 2022 - 02:33 PM.


#2 RedLionNJ

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Posted 04 October 2022 - 11:27 AM

Don't use a diagonal.  If you haven't already read the FAQ, I suggest perusing it at some length (or depth).

 

Starting with the scope itself, the focuser should come next, then the barlow, then the ADC, then the cam.  The IR-cut filter can come anywhere.

 

You won't know what focal ratio you're going to get until you assemble all the pieces and take an image.  Your f/10 C6 is not going to be f/10.

 

A 2x barlow is a bit on the high side for this setup. You won't often get maximum use out of it.

 

Finally, the 585 has a LOT of pixels. Jupiter shouldn't cover more than about 200 at most.


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#3 Subspace

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Posted 04 October 2022 - 12:37 PM

FAQ shows: Eyepiece adapter ---> (focuser) ---> filter ---> (ADC) ---> Barlow ---> camera.

 

What is a "focuser"? FAQ does not elaborate. Do I need one or can I manually focus using the focus knob?

-I see these online: EAF or Helical focuser. I am not using auto guiding yet. I will be will using the built in tracking that comes with synscan wifi mount. Can you provide me with a link on what kind of focuser I need?

 

Also the FAQ mentions "Eyepiece adapter". Is this the same as 1.25 Nosepiece that comes with the camera?

 

Also if I increase the barlow to 3x, then Jupiter will be more than 200 pixels? Does the image degrade due to oversampling since I am much higher than the recommended f ratio for the camera's 2.9 um?

 

Thank you


Edited by Subspace, 04 October 2022 - 02:34 PM.


#4 Borodog

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Posted 04 October 2022 - 04:14 PM

Where the eyepiece or camera inserts is the focuser it is talking about. In your C6 the focuser is actually the knob the moves the primary mirror internally, but they are using refractor or Newtonian terminology, where the entire draw tube moves to focus.

#5 Tulloch

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Posted 04 October 2022 - 04:39 PM

FAQ shows: Eyepiece adapter ---> (focuser) ---> filter ---> (ADC) ---> Barlow ---> camera.

 

What is a "focuser"? FAQ does not elaborate. Do I need one or can I manually focus using the focus knob?

-I see these online: EAF or Helical focuser. I am not using auto guiding yet. I will be will using the built in tracking that comes with synscan wifi mount. Can you provide me with a link on what kind of focuser I need?

 

Also the FAQ mentions "Eyepiece adapter". Is this the same as 1.25 Nosepiece that comes with the camera?

 

Also if I increase the barlow to 3x, then Jupiter will be more than 200 pixels? Does the image degrade due to oversampling since I am much higher than the recommended f ratio for the camera's 2.9 um?

 

Thank you

Note the focuser is in brackets, it's an optional accessory to have an external (Crayford style) focuser. It's not essential, but it might make focusing easier, in the meantime just use the focus knob on your C6. Before I got my Celestron electronic focuser (which turns the focus knob from the hand controller) I found a piece of pipe insulation foam and a long hairclip worked well.

https://www.cloudyni...022/?p=12142483

 

The eyepiece adapter is the visual back, I prefer that terminology...

 

If you get a 2x barlow, unscrew the front element and screw it into the camera nosepiece, you will get around 1.5x magnification which is great for the 585. Don't forget the IR-cut filter.

 

Andrew




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