ASI2600MM - EFW & Skywatcher F4 Coma Corrector Backfocus

[Batteredburrito]

Hi all,

New to the hobby and forum, need a little help with setting up and configuring the kit in the title.

Using an 8" Quattro F/4 and the Skywatcher Coma Corrector. Suffering miserably currently with edge of view star warping.

 

Have tried the following two configurations (all distances in mm):

Config 1			Config 2
Camera	12.5		Camera	12.5
EFW	20		Tilt Plate	5
Filter	1		Adapter	2
Adapter	22.5		EFW	20
Coma	0		Filter	1
			Adapter	16.5
Total	56		Total	57
Required	56		Required	56

 

Required backfocus for the CC is 55mm as is the camera but struggling with getting the images with the above configs to look decent. Still have severe warping at the edges of the image.

Anyone with more experience and expertise on this would love to get your thoughts or even someone with the same kit. Havent been able to find any help with this currently.

 

Many thanks

[Stefan73]

The contribution for the ASI2600MM Pro to the back focus is 17.5mm....

https://astronomy-imaging-camera.com/product/asi2600mm-pro-mono

[Batteredburrito]

2 minutes ago, Stefan73 said:

The contribution for the ASI2600MM Pro to the back focus is 17.5mm....

https://astronomy-imaging-camera.com/product/asi2600mm-pro-mono

Indeed, it has a title plate included that is 5mm, with it removed and the efw bolted directly on, its 12.5mm, 17.5mm with the black plate. Have tried both configs

[Stefan73]

49 minutes ago, Batteredburrito said:

Indeed, it has a title plate included that is 5mm, with it removed and the efw bolted directly on, its 12.5mm, 17.5mm with the black plate. Have tried both configs

Ah fair enough.  Which skywatcher coma corrector do you mean?

https://www.firstlightoptics.com/coma-correctors/skywatcher-coma-corrector.html

or

https://www.firstlightoptics.com/coma-correctors/skywatcher-f4-aplanatic-coma-corrector.html

The first seems to not be good enough for F4 scopes from the reviews.  Otherwise maybe post an example sub to show the effect.

[Batteredburrito]

13 minutes ago, Stefan73 said:

https://www.firstlightoptics.com/coma-correctors/skywatcher-f4-aplanatic-coma-corrector.html

This one is the one I have

Please see below subs on the configurations:

 

Image - Configuration 1

Configuration:

2600MM Without Backplate -> EFW -> 22.5MM Extender -> Coma Corrector

 

Image - Configuration 2

Configuration:

2600MM With Backplate -> 2MM Spacer -> EFW -> 16.5MM Extender -> Coma Corrector

 

Apologies if these images are naff, still learning as I go only have these two subjects currently

Edited January 29, 2023 by Batteredburrito
Image clarification

[Starflyer]

I've only taken a quick look on my tablet but it looks like you have some pretty bad sensor tilt, this will affect your ability to judge and set your backspacing properly.

If it were me I'd analyse the subs in ASTAP to get a handle on the tilt and find where it's coming from / how to correct it before going on to tweak the spacing.