ED72+ATIK HORIZON+FF/FR Spacing

[Marky1973]

Finally managed to find a bit of time to have a play after getting the Horizon back from Atik and not being too tired or full of cold to be bothered to set things up. As it was, I was still fighting against the un-forecast clouds that started rolling in.

My main aim tonight was just to shoot a couple of subs to check the corner stars to see whether or not the spacing was right. 

The set up is....

Atik Horizon > Filter Wheel > FF/FR > FF/FR Adaptor > Draw Tube

The adaptor for the reducer is the one that comes with the ED72 reducer (aka the ED80 reducer) and adds a few mm to the overal length of the imaging train.

I started with the above set-up using the spacing that I previously had c. 57mm from sensor to the rear edge of the FF/FR - a quick set-up and 3 minute sub gave me the following:

 

 

This is a close in crop of the top left of the sub which clearly shows the stars are pointing into the centre of the image. My understanding meant that this means the distance from sensor to FF/FR is too close.

So, a couple of spacers later and the distance from the Sensor to rear edge of the reducer is now 59mm. Another 3 minute image, scupper by clouds (and of a different patch as I was rushing and had to take the scope down to adjust it) and the stars look a lot better.

So I think this might have cracked it. I need to get out and try again with more time to see if further subs repeat this, but I am keeping my fingers crossed that this is right as there is very little play left in the draw tube for further adjustments.

I also discovered that the focuser now won't hold everything solid as the reducer adds too much weight, so need to sort that out and using the adapter for the FF/FR and the lack of rotation in the focuser, means I have to have things at an odd angle to line up the top of the sensor with the top of the scope. I am sure there is a solution to that with upgraded focusers etc, but I'll have to stick with what I have now.

Anyhoo, hope this is helpful for anyone with a similar set-up, or considering something similar. I guess it will be different for those with a ZWO 1600 as the back focus on the 1600 is shorter that the HORIZON (iirc).