Is it tilt?

Acquisition Deep Sky Collimation Coma Tilt Troubleshooting
11 replies•142 views
John Tucker avatar
John Tucker avatar

Working on transitioning from more or less EAA to better astrophotos. Last night was remarkable seeing for this part of Florida, was able to get my guiding down to an average of about 0.4 for the entire night and down below 0.3 for extended periods.

The Whirlpool galaxy is an overworked target, and there is nothing unique or creative about this framing, but it was a good opportunity to test out my new Nexus focal reducer. My stars have tails that get worse as one goes from upper right to lower left. Is it tilt? I just finished a careful collimation of the scope and have checked that the corrector plate and secondary mirror have the correct rotational alignment iwth the primary mirror.

I’m not going to complain about the OTA. I picked it up for $100 used from a guy who only wanted to sell locally.

📷 image.png📷 image.pngimage.png

1📷 image.pngimage.png

Helpful Engaging
andrea tasselli avatar
andrea tasselli avatar
Looks like coma. Tilt usually ends up showing astigmatic stars.
John Tucker avatar
John Tucker avatar

andrea tasselli · Mar 15, 2026, 02:33 PM

Looks like coma. Tilt usually ends up showing astigmatic stars.

Can it be fixed or is that just the price of doing AP with a $100 OTA?

andrea tasselli avatar
andrea tasselli avatar
Does it show without reducer? If it does and if the collimation is spot-on then yes, that is an issue. I suppose that you being in FL temperature equalization isn't a concern there but in case it is are you sure the scope has reached thermal equilibrium?
John Tucker avatar
John Tucker avatar

andrea tasselli · Mar 15, 2026, 02:47 PM

Does it show without reducer? If it does and if the collimation is spot-on then yes, that is an issue. I suppose that you being in FL temperature equalization isn't a concern there but in case it is are you sure the scope has reached thermal equilibrium?

We have massive dew problems here and I had the heater on the dew shield turned up pretty high. I’ll look into that, thanks!

Well Written Respectful
TiffsAndAstro avatar
TiffsAndAstro avatar
John Tucker:
Working on transitioning from more or less EAA to better astrophotos. Last night was remarkable seeing for this part of Florida, was able to get my guiding down to an average of about 0.4 for the entire night and down below 0.3 for extended periods.

The Whirlpool galaxy is an overworked target, and there is nothing unique or creative about this framing, but it was a good opportunity to test out my new Nexus focal reducer. My stars have tails that get worse as one goes from upper right to lower left. Is it tilt? I just finished a careful collimation of the scope and have checked that the corrector plate and secondary mirror have the correct rotational alignment iwth the primary mirror.

I’m not going to complain about the OTA. I picked it up for $100 used from a guy who only wanted to sell locally.

📷 image.png📷 image.png

1📷 image.png


What scope, and do you have a guide log?
I only ask as I recently got similar stars, but my guiding showed a BIG ra spike every few seconds.
John Tucker avatar
John Tucker avatar

TiffsAndAstro · Mar 15, 2026, 05:50 PM

John Tucker:
Working on transitioning from more or less EAA to better astrophotos. Last night was remarkable seeing for this part of Florida, was able to get my guiding down to an average of about 0.4 for the entire night and down below 0.3 for extended periods.

The Whirlpool galaxy is an overworked target, and there is nothing unique or creative about this framing, but it was a good opportunity to test out my new Nexus focal reducer. My stars have tails that get worse as one goes from upper right to lower left. Is it tilt? I just finished a careful collimation of the scope and have checked that the corrector plate and secondary mirror have the correct rotational alignment iwth the primary mirror.

I’m not going to complain about the OTA. I picked it up for $100 used from a guy who only wanted to sell locally.

📷 image.png📷 image.png

1📷 image.png



What scope, and do you have a guide log?
I only ask as I recently got similar stars, but my guiding showed a BIG ra spike every few seconds.

I’ve never been able to figure out how to generate/find a guide log on the ASIAIR. But the seeing was outstanding, and everytime I looked at the guiding it was below 0.5 arc seconds and never saw a spike greater than 1 arc second. Probably overall the best guiding I’ve ever gotten.

This is an old carbon fiber C8 that I picked up used. The collimation was all screwed up, in part because the secondary had been rotated out of position, so I tuned it up as best as I could.

Well Written Respectful Engaging
andrea tasselli avatar
andrea tasselli avatar
John Tucker:
We have massive dew problems here and I had the heater on the dew shield turned up pretty high. I’ll look into that, thanks!


That could be quite likely, given that at the resolution of the pic I can't tell if it's one or the other. Insulated dew shield, reflective insulation and dew strip kept at minimum are the best way to combat dew (see this thread: Reaching Out to John Hayes - AstroBin)
Helpful
John Tucker avatar
John Tucker avatar

Looks like the problem(s?) varied over the course of the night, so probably something thermal. 📷 image.pngimage.png

andrea tasselli avatar
andrea tasselli avatar
Yeah, I'm pretty positive about that.
Craig Towell avatar
Craig Towell avatar

Also agree on the thermals as cause of those flares.

BTW on ASIair if you go into the memory the guide log files are in here…

📷 IMG_1583.jpegIMG_1583.jpeg

John Tucker avatar
John Tucker avatar

Craig Towell · Mar 15, 2026, 08:15 PM

Also agree on the thermals as cause of those flares.

BTW on ASIair if you go into the memory the guide log files are in here…

📷 IMG_1583.jpegIMG_1583.jpeg

thanks!