8" Edge HD - First Light

[boz_m]

Hi all,

I recently got a second hand 8" EdgeHD SCT as well as the 0.7x reducer. I have heard the EdgeHD has a great flat field without the reducer.

I got my first opportunity last night to give it a whirl with the 0.7x reducer on there and a full frame Canon 6D camera. I was taking shots in the middle of Sydney so the shots aren't great, but i was more testing the flatness of the field and the quality of the picture. Find attached an example shot. It does seem much flatter than my old C8 that i had but i expected it to be fully flat.

It looks like it still has a few issues with flatness. Can more learned people have a look at this photo and let me know if there are issues with coma or other issues with the FOV? Is there anything i can do to make my raw shots look better with rounder stars (collimation looked ok btw)? Should i be using the EdgeHD without the reducer to get a full flat field (but that limits what i can look at and makes tracking more difficult at the longer focal length)?

Image here (size was too bid for this site):
https://imgur.com/a/R1qqfkh

Any tips appreciated!!!!!
Cheers

[Atmos]

I believe the 0.7x reducer on the Edge 8” is optimised for crop sensors and not full frame.

[boz_m]

Cheers

can you see the sort of flaring of the stars when you zoom in? This seems to be pretty consistent across the FOV and similar in most of my photos taken the other night. Is this a tracking issue or something more?

https://imgur.com/a/lTN6mfd

[billdan]

Hi Alex,

I had a quick look at your first image and at first glance it is obvious that in future, you will have to make a stack of flat frames to eliminate the vignetting you have.

I could not see any coma but I believe you may have a camera tilt issue, the eccentricity of the stars look good in the centre and bottom left and right, but the top corners looks a lot worse which suggests camera tilt.

You can buy tilt adapters to clear this up, but maybe wait and see what others say first, in case I'm wrong.

Cheers
Bill

[boz_m]

cheers Billdan,
Yeah when i process the images i stack them together using DeepSkyStacker and include flats, bias and darks. Interesting about camera tilt. I haven't looked into that yet but will check it out.
Cheers, Alex.

[billdan]

Your second image looks like a hint of coma in the top left.

Whilst its best practice to eliminate these problems at the source, you can also repair stars in post processing.
I use Astroart v5 for my stacking and it has a module for making the stars round, Startools which I use for post processing also has a star repair module.

[glend]

I agree there is vignetting. Do you have an APS-C camera to try? I am not convinced your in focus in that shot. Do you have the spacing correct? The reducer spacing is different to the f10 spacing.

There are many threads on Cloudy Nights concerning Edge HD reducer spacing and effects. Here is one:

https://www.cloudynights.com/topic/552733-c8-edge-hd-wreducer-back-focus-question/

[boz_m]

will look at the spacing. cheers.