Using an EAF for Imaging Spectra?

Science Spectroscopy
1

Hello, everyone. I’m hoping to get some opinions on how to best approach this, please.

I’m a total newcomer to imaging, and I’m trying to set up my rig with the goal of collecting spectra once I figure out how to take images. I just got my first test images (yay!), so I know it all functions, now I have to figure out the details.

I own a ZWO EAF but have not attached it to my telescope yet. My understanding is that an EAF autofocuses based on the apparent size (pixels) of stars. If there are times when a spectrum might need a slightly different focus than its star does, will I be able to focus on a spectrum using an EAF? Or will it just make things more complicated to use one? I’m using an ASIAir Mini. At first I suppose I could manually focus how I need to with the EAF, but will autofocus ever be an option for this?

Before I get things too dialed in with my rig, I’d like to install the basic things I’ll be using so I don’t have to redo the backspacing each time. Backspacing is my bane. So I was wondering if people find an EAF useful for collecting spectra?

Thanks for your time!

-Katie Z.

2

What spectrograph are you using?

Steve

3

I have an SA-100.

-Katie

4

It’s never easy.

Go to Tom Field’s videos here - RSpec videos - RSpec / Real-time Spectroscopy
and watch video #7

In short the star shouldn’t be focused the spectrum should.

I use an electronic focuser, and I tweek it manually while lookiong at the live image in sharpcap to sharpen the spectrum features.

My star is always a little out of focus.

Steve

5

For example here is a screenshot from RSpec, the star is an oblong blob but the spectrum has definition.

Screenshot 2025-04-14 002627
Screenshot 2025-04-14 0026273626×1790 205 KB

1 Like
6

Katie, this spectrum looks good. RSpec has a feature for focusing on the lines, but the idea is just to get the lines to be as deep and sharp as possible.

7

Thank you, everyone, I appreciate it! It looks like focusing on the spectrum with an EAF will have to be done manually in my situation then. It’s still likely to be tons better than I can do manually without one, though, so I’ll put it on and see how it works out.