ZWO eaf settings for EdgeHD 8

Hi,
1. There’s no absolute "zero" position on the focus knob itself—it’s just a reference point. You can set the EAF (Electronic Automatic Focuser) to zero at any time. From that reference point, you can command the EAF to move up to its maximum range (e.g., 60,000 steps).

Since the focus point depends on your setup (and it changes between using a camera or an eyepiece), you'll need to find focus manually. To do that, point your telescope at a distant object during the day, or a bright star at night. Then manually focus using either the knob or the EAF until the object is sharp.

Once you've found focus, you can assign that position any value you like in the EAF software. For example, I set mine to 10,000, which gives me flexibility to adjust focus both inward and outward (especially useful if I switch between a 0.7× reducer, no reducer, or a 2× Barlow).

If you're focusing on a star and your camera software supports real-time preview, it’s much easier: just slowly move the EAF while watching the star. You’ll see the donut shape of the out-of-focus star grow or shrink—your goal is to minimize that ring, and that tells you which direction to turn.

2. Does the Maximum or Minimum Position Matter?
Not really. In my experience, I’ve never hit the actual mechanical max or min of the focus knob—even when using a reducer or Barlow lens. The ZWO EAF, for example, can move well over 12,000 steps, which is plenty of range for most setups.

So don’t worry too much about the limits. As long as your telescope can reach focus with your current configuration, you’ll rarely (if ever) need to max out the EAF travel.

3. Once you’ve roughly found focus, it’s important to lock the EAF securely onto the focus knob—any slippage between them will throw off your EAF readings. After securing it, you can calibrate backlash using the following method:

Mark the knob and the EAF coupler with a piece of tape or marker so you can visually track movement.
From your control app, move the EAF 100 steps in one direction, then move it 100 steps back.
If the two marks realign, your backlash is essentially zero.
If they don’t, continue turning the EAF (same direction) until the marks align again.
The number of extra steps required is your backlash value.
Repeat the process a few times for consistency. Once you have a reliable value, enter it into your EAF software.
This ensures your autofocus routines and manual adjustments are accurate and repeatable.

Hope this is helpful!
Good luck and enjoy!

Peng

Agreed with @MaxSpektro  I also took it out and now I go all manual and do all fine tuning when needed.

Paul Larkin:
Hi, Amit.

I had the ZWO EAF on my EdgeHD 8 (C8) and it worked well enough, but I switched to the Esatto 2 LP – MaxSpektro is spot on with his comments.  It’s a beautiful piece of kit but it is pricy so maybe not a consideration for now.  Works flawlessly with NINA.

But back to the EAF.   I keep a log, and as best I can tell from my notes, the settings I ended up using on for the EAF on the C8 were as follows (NB: I use NINA, not ASIAIR but I expect the same parameters will apply):

·       Autofocus Step Size=250

·       Initial Sets = 4

·       Backlash compensation method = Overshoot

·       Backlash IN/OUT = 0/500

A note on Backlash.  For the C8, you need OUT set to something (not IN).  I tried smaller and larger values, but 500 worked on mine: anticlockwise needs to be the final move to deal with backlash on the C8 and this is the correct setting for that.

If it helps, I also use the Hyperbolic curve  fitting algorithm, which for me works better then the other options available in NINA – this may be a NINA thing, so you may need something else.

I hope that helps, Amit.

All the best.

Paul

ASIair automatically calculates backlash compensation IN/OUT and method, Only adjustments you need to make (or in this case, can make) are the Step Size and interval of AF.

I use step size = 50, gives me laser sharp AF every time.

I'd advise every 30m to 1h per AF, since you can't lock the mirror when using an EAF.