6 replies to this topic

[jamiejako]

I attached the ZWO EAF to my Celestron EdgeHD 11 and tried imaging last night, and I’m now getting oblong stars.

 

My imaging train is: ASI2600MC Duo, ZWO 5x2 EFW, M54 manual rotator, 9mm M54 spacer, SCT to M54 adapter, 0.7x reducer — mounted on a ZWO AM5 and controlled using ASIAir. Backfocus should be exactly 146.05 mm.

 

Here's a picture of my rig: 

 

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I imaged before attaching the EAF to confirm backfocus and collimation, and saw fairly round stars (just a few dust spots). I manually focused and locked the mirror. 
Here’s a picture before attaching the EAF: 

 

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I then took off the scope, attached the EAF, and ran a full cycle from 0–60,000 and back to test if it was working properly. I also checked backlash by moving 200 steps forward and back — it landed on the same spot, so I left backlash at 0. I cleaned the reducer glass (there was visible dust), and remounted the scope.

This time, I ran the autofocus routine using the EAF, leaving the mirror unlocked. Right after autofocus finished and I started imaging, I noticed oblong stars across the frame. 
Here’s a picture after attaching the EAF: 

 

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I didn’t touch collimation, backfocus, or anything else in the imaging train. I have fans installed on the air vents, and waited up to an hour for the scope to cool down. Guiding was decent around 0.7–0.8" in both cases.

Is this how mirror flop usually shows up? Any pointers on how to diagnose and fix this would be appreciated.

[pyrasanth]

This may sound obvious but were the mirror locks fully disengaged before running the mirror focus backwards & forwards- some tilt may have been introduced when the mirror moved. Sometimes the locks can become sticky so check that aspect. I would also consider changing the mirror locks to the low profile Optec brass locks- they lock better and release better.

 

What I did when I saw this was to point the scope vertical & allow the mirror to settle under gravity for a couple of hours- this levelled the mirror.

 

The problem with moving the mirror such a long way initially is that it can tip slightly- enough to see this issue.

 

I found it so annoying with big focus changes that I changed focusing to the Optec SMFS which allows me to lock the main mirror and focus with the secondary mirror.

 

Good luck with fixing this issue.

Edited by pyrasanth, 26 April 2025 - 04:21 AM.

[jamiejako]

I can think of a couple things to consider.

 

When you fitted the EAF did you account for the increased back focus?- you need to be at 146 mm plus or minus a couple of mm either way. If you did not alter the back focus spacing and you were correct before the EAF fitting then this will be enough distance increase to cause the issue you are seeing. My testing on the C11 & now the C14 dictates that I need to be within +/-5 mm.

 

The EAF, in common with many new components, can introduce tilt which you may need to compensate for. Check that that any removed and refitted components are screwed all the way down snugly and the threads turn smoothly just as a check for any cross threading.

 

Good luck with finding the cause and fixing.

 

Thank you for your reply. I attached the EAF on the primary focus knob by following this video: https://youtu.be/_uC8DI7Enlg

My imaging train is exactly the same before and attaching the EAF. Would attaching the EAF on the focuser knob require backfocus adjustment?

[pyrasanth]

Thank you for your reply. I attached the EAF on the primary focus knob by following this video: https://youtu.be/_uC8DI7Enlg

My imaging train is exactly the same before and attaching the EAF. Would attaching the EAF on the focuser knob require backfocus adjustment?

No- my initial post was incorrect. I miss read what equipment you had fitted (mind elsewhere!) so I corrected the post. Fitting the EAF would have no bearing on the back focus as it is not an optical train in path component. The issue is more likely that the mirror has tilted slightly and you need to let gravity settle the mirror.

[DeepSky Di]

I did similar steps when I fitted EAFs to my SCTs - turned the knob all the way one way and counted the turns to the other end of travel and then focused on as far away as I could in daylight (not far in my case) and counted the turns to that. Then counted EAF steps per turn. 

 

There is a firmware update for the EAF that increases the step count to 300,000. I was able to install it via ASI Studio on Mac. 

[jamiejako]

No- my initial post was incorrect. I miss read what equipment you had fitted (mind elsewhere!) so I corrected the post. Fitting the EAF would have no bearing on the back focus as it is not an optical train in path component. The issue is more likely that the mirror has tilted slightly and you need to let gravity settle the mirror.

 

I followed your advice, and left the scope upright to let the mirror settle. I tried imaging last night and it was much better, back to getting mostly round stars. I got great guiding at 0.5" and 1 hour of good subs before meridian flip. After the flip, the EAF routine ran and the elongated stars came back. I will look into solutions for locking the mirror like the Optec you suggested or external focusers. Thank you for the guidance!

[jamiejako]

Adding an update to this thread:

I found finishing focus counter-clockwise mitigates tilt to an extent by allowing the mirror to settle correctly. My EAF routine was already finishing counter-clockwise, but I assume it doesn't solve the tilt problem since the movements are small. I was able to do this by moving the EAF 2 coarse steps up and back down after any major slewing - then running the AF routine again.

I have added some images in my troubleshooting album to demonstrate: 

Album: Troubleshooting

2 images

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