Eggy stars - my sensor too close?

[AstroNebulee]

Hi

I have eggy stars in mainly the top two corners but can see them eggy in the bottom corners now I can zoom in better. If you look at the core of the stars around the edge of the image you can see the drift off to the edge. Am I right in thinking that the sensor is too close to the FF. The images are single 3mins subs stretched I am using the correct 55mm of back focus but may need to use the shims provided with my zwo asi294mc pro. 

I took an inage with the camera rotated 90 degrees right and the same. My set up is sw 72ed AzGti eq mode zwo asi 294mc pro. 

 

 

[michael8554]

I'd say the bottom left corner is correct, the other corners are tilted.

So leave bottom left alone and correct the tilt in the other corners .

That may be difficult, so do your best with the tilt, then add/subtract mm's to correct any coma.

Michael

[david_taurus83]

Are you not using a filter? Looks like a fair bit of fringing on your stars. Certainly won't help with the elongation as it's adding to the issue.

[AstroNebulee]

52 minutes ago, michael8554 said:

I'd say the bottom left corner is correct, the other corners are tilted.

So leave bottom left alone and correct the tilt in the other corners .

That may be difficult, so do your best with the tilt, then add/subtract mm's to correct any coma.

Michael

I'd find it hard to correct the tilt in 3 corners as I have no tilt adjuster fitted. Inhave a rotator for my scope and wonder if fitting this may help instead of the visual back on there now. As my FF has a chamfered edge to it so when the thumbscrews connect coukd cause the tilt? (see attached image). 

33 minutes ago, david_taurus83 said:

Are you not using a filter? Looks like a fair bit of fringing on your stars. Certainly won't help with the elongation as it's adding to the issue.

I am using a svbony 2 in H ir uv cut filter attached to my FF but I have a zwo 1.25inch ir uv cut filter I coukd attach to the camera via the filter adapter. 

[Chefgage]

I have the exact same issue. I put it down to tilt. I too use the exact same image train as you. I do have an adapter from Flo that does away with the thumb screws that hold in the field flattener. You unscrew the black round connector with the thumb screws in the 72ed and replace it with an adapter that the field flattener can screw into. Not sure if this fixes the tilt issue as I have not tried mine yet. The only issue is then you cannot rotate the camera for framing. But as you have a rotator this might be an option.

[AstroNebulee]

2 hours ago, Chefgage said:

I have the exact same issue. I put it down to tilt. I too use the exact same image train as you. I do have an adapter from Flo that does away with the thumb screws that hold in the field flattener. You unscrew the black round connector with the thumb screws in the 72ed and replace it with an adapter that the field flattener can screw into. Not sure if this fixes the tilt issue as I have not tried mine yet. The only issue is then you cannot rotate the camera for framing. But as you have a rotator this might be an option.

I am going to try the rotator as a next step and see if this helps my issue. I have adjusted more tension previously to my focuser as it was slipping a bit when tightening the focus lock up. So solved that issue but had the eggy stars before this. I am in contact with FLO too and they have said a tilt adjuster and my rotator could solve the issue but want to try the rotator first to see if this solve it before shelling out for a tilt adjuster but I may need to. I'm wondering if adding a shim that was supplied with my camera would help though. 

Edited January 29, 2022 by AstroNebulee

[alacant]

5 hours ago, AstroNebulee said:

eggy stars

Loosen the grub screws on the focuser retainer (the silver coloured ring) and reseat it, tightening in small increments. That usually does it.

Cheers

[AstroNebulee]

20 minutes ago, alacant said:

Loosen the grub screws on the focuser retainer (the silver coloured ring) and reseat it, tightening in small increments. That usually does it.

Cheers

Thank you sorry for being a bit dense here could you point out on my image as to which grub screws you mean 

[alacant]

3 hours ago, AstroNebulee said:

which grub screws

3 off.

Move the tube rings too of course so as to give some wiggle factor.

Adjust until a laser collimator in the focuser is exactly central in the objective lens; use a circular, centre-marked paper mask to see where the beam hits the lens.

Edited January 29, 2022 by alacant

[AstroNebulee]

1 hour ago, alacant said:

3 off.

Move the tube rings too of course so as to give some widdle factor.

Thank you Alan, I'll give this go 👍

[rickwayne]

Ugh, I can't find that handy image that shows which way the stars point when you're too close or too far away from your flattener. I think the stars do a pincushion thing (streaks oriented radially) when you're too close and a barrel thing (streaks oriented around circumference of image) with too much spacing, but could be the other way 'round, too.

Probably not your issue, but it's worth surfacing now and then for other folks who're trying to diagnose problems in image trains including a flattener.

[AstroNebulee]

6 minutes ago, rickwayne said:

Ugh, I can't find that handy image that shows which way the stars point when you're too close or too far away from your flattener. I think the stars do a pincushion thing (streaks oriented radially) when you're too close and a barrel thing (streaks oriented around circumference of image) with too much spacing, but could be the other way 'round, too.

Probably not your issue, but it's worth surfacing now and then for other folks who're trying to diagnose problems in image trains including a flattener.

Yep, this is what I found at the weekend trawling the net, why it made me think sensor a tad close, but think it's a tilt issue, I've since fitted a rotator to fix the imaging train tight and will try this next before I go further. 

[AstroNebulee]

On 29/01/2022 at 11:48, Chefgage said:

I have the exact same issue. I put it down to tilt. I too use the exact same image train as you. I do have an adapter from Flo that does away with the thumb screws that hold in the field flattener. You unscrew the black round connector with the thumb screws in the 72ed and replace it with an adapter that the field flattener can screw into. Not sure if this fixes the tilt issue as I have not tried mine yet. The only issue is then you cannot rotate the camera for framing. But as you have a rotator this might be an option.

Hi, have you had a chance to try your scope tilt issue yet. I had a very brief go tonight with mine. I connected the rotator this time to my scope. So the imaging train is zwo 2 inch ir uv filter, screwed into rotator, the FF screwed on the correct 55mm back focus to 294mc pro. Tried on 60 second exposures still eggy in top right and left corners. Then tried the sims that came with the osc one by one, drill same issue. So my reckoning it's either tilt in the focus tube or tilt of the sensor. I've ordered a zwo tilt adjuster from FLO, so if I still have the same issue after using that it's got to be the focus tube. Guiding was good tonight so not that. 

[AstroNebulee]

On 29/01/2022 at 11:48, Chefgage said:

I have the exact same issue. I put it down to tilt. I too use the exact same image train as you. I do have an adapter from Flo that does away with the thumb screws that hold in the field flattener. You unscrew the black round connector with the thumb screws in the 72ed and replace it with an adapter that the field flattener can screw into. Not sure if this fixes the tilt issue as I have not tried mine yet. The only issue is then you cannot rotate the camera for framing. But as you have a rotator this might be an option.

Just an update on my thread, I've downloaded ccd inspector and ran through my first image before any adjustments and my last image with shims added and a tweak of the grub screws for the top bearing rollers. I'll attach the relevant screenshots. Betelgeuse was my adjusted image and NGC 2244 was the first one unaltered. Any thoughts. On a side note I'm going to try my laser collimator through the scope today to see how centered it is. 

 

 

 

 

 

 

Edited February 5, 2022 by AstroNebulee

[AstroNebulee]

Hi @alacant

Update to my post above. I have used my laser collimator (never thought I'd use that again and was still collimated too) and made a paper mask to carry out your suggestion of reseating the focus tube mechanism. I undone all the grub screws took the mechanism out then reseated until the laser beam was hitting the centre mark then carefully tightened each grub screw until held firmly in place. 

My first image shows before any adjustments and last image shows the final position, still not perfectly centred but much better than it was. I'm hoping this may help my issue. I still have a zwo t2 tilt adjuster on order incase of finer adjustments needed. 

[alacant]

3 hours ago, AstroNebulee said:

last image shows the final position

Hi

Yes. Well done.

You could also see the 'non-centred-ness'  on your curvature plots. Did you try with the focuser at differing extensions? If so, and the laser remained central, you're good to focus (sorry!) attention on the ff spacing.

Cheers

Edited February 5, 2022 by alacant

[AstroNebulee]

29 minutes ago, alacant said:

Hi

Yes. Well done.

You could also see the 'non-centred-ness'  on your curvature plots. Did you try with the focuser at differing extensions? If so, and the laser remained central, you're good to focus (sorry!) attention on the ff spacing.

Cheers

Hi 

Yep, I kept racking the focuser in an out to check and stayed in place. The screen shots from ccd inspector were before my adjustments with the laser collimator, so will have to test these when I get clear skies again. I shall use the recommended 55mm of back focus spacers first 17.5mm from sensor, 21mm & 16.5mm ones. 

Cheers 

Lee 

Edited February 5, 2022 by AstroNebulee

[AstroNebulee]

[AstroNebulee]

Still got the issue with eggy stars after the collimation which is centred. Tried adding the spacers provided with the camera but still the same. The stars seem eggy more uniform now suggesting back focus isn't enough, think I may need 5mm more so 60mm back focus possibly? I'm losing the will to carry on and just accept the eggy stars or give up. 

Edited February 23, 2022 by AstroNebulee

[alacant]

49 minutes ago, AstroNebulee said:

accept the eggy stars or give up

Hi

The 72ed is bottom of the range material and you may just have a poor example. Perhaps go along to an astro club and do a side by side with an example which is known to work ok?

Anyway, setup the imaging train vertically so the the components sit under gravity. Give a final tighten whilst shaking the assembly. 

Have you drilled and tapped a third thumbscrew in the focuser collar yet?

You're very nearly there. Your 5mm idea may just do it. Post a frame from the camera if you like. Then we may be able to advise better.

Cheers

[AstroNebulee]

5 hours ago, alacant said:

Hi

The 72ed is bottom of the range material and you may just have a poor example. Perhaps go along to an astro club and do a side by side with an example which is known to work ok?

Anyway, setup the imaging train vertically so the the components sit under gravity. Give a final tighten whilst shaking the assembly. 

Have you drilled and tapped a third thumbscrew in the focuser collar yet?

You're very nearly there. Your 5mm idea may just do it. Post a frame from the camera if you like. Then we may be able to advise better.

Cheers

Hi Alan 

It would be just my luck to have a poor example. 

Regarding astro clubs, I don't drive and live in rural Cornwall so not very easy atall. 

I don't use the thumbscrew focuser collar, I use a rotator so there's no chance of flexibility in the imaging train. I still on theibrs of thinking a 5mm spacer us needed as I'm sure I saw online somewhere someone mention 60mm back focus for 72ed, ovl FF and 294mc pro. After some trawling on here I've found this thread about the rotator I have and @Skyline @StarlightHunterhas the same set up as mine and uses 60mm back spacing, so sent a pm to ask his advice too.

Thikk my 72ed is the oldee long tube version (there's no rotator sticker) but the rotator fits perfectly. 

I shall add an image from last night as soon as I get home. 

Lee 

Edited February 23, 2022 by AstroNebulee

[FLO]

On 29/01/2022 at 12:01, AstroNebulee said:

I am in contact with FLO too 

 

4 hours ago, AstroNebulee said:

It would be just my luck to have a poor example. 

I might be wrong but I don't think your telescope, reducer or camera were purchased from FLO. Is your supplier aware of the problems you are having? 

Steve 

[AstroNebulee]

1 hour ago, FLO said:

 

I might be wrong but I don't think your telescope, reducer or camera were purchased from FLO. Is your supplier aware of the problems you are having? 

Steve 

Hi Steve

I replied in the other thread, Alex at flo is kindly helping me with this issue. I bought the scope in the classifieds here last year and camera from RVO as it was in stock there. I'll be sure to let RVO know the issues to. I hope I didn't come across as buying the items from you and complaining at your service, I'm sorry if it did. 

Cheers 

 

Lee 

Edited February 23, 2022 by AstroNebulee

[AstroNebulee]

Hi @alacant here attached is a single 3 minute sub from last night (just a light and dark stacked no flat or flat dark) with my current filter, rotator, ovl field flattener, 55mm of back focus and 294mc pro. If you zoom in, the stars are all pointing from the centre of the image, so I think it needs more back focus. The image is easier to see the issue on a laptop screen as much bigger. 

Cheers 

Lee 

 

Edited February 23, 2022 by AstroNebulee

[AstroNebulee]

Added a 5mm spacer to the imaging train now and hoping the total 60mm of back focus will cure the eggy stars. A few other members with the exact same set up had to use 60mm to cure their issues, so hoping its cured mine too, really need a clear night to test it all now.