"First light" with Touptek IMX571 - what is going wrong - cont'd ...

[AstroRookie]

Hello,

I bought a second hand Touptek IMX571 (can't remember the real model name but for the problem here that is not relevant, I presume) in August 2023, got scammed (previous owner advertised the camera with pictures of an identical one that did not have the protective glass scratched, but that is an other story), had to send it via teleskop-express.de (big thumbs up for them) to the manufacturar and finally got it back in November. Real first light was just to find out that I could not get focus, so had to buy some extra adapaters. Second first light, I realized that adapters and camera were not held straight in the focuser, so bought an adapter which allows me to screw every thing tight in the focuser.

All this during the last 3 months with hardly any clear nights ... So yesterday and with the upcoming beautiful 2 nights, I thought it's now or never ... and alas, it looks more like never ...

So here's my setup:

• Telescope: Orion 8" astrograph
• Coma corrector: Baarder MPCC Mark III
• Camera: Touptek ATR3CMOS26000KPA (IMX571)
• I collimated the scope with the Farpoint collimation tools
• 20 light frames - 300s  processed with darks, bias, flats - not really relevant the the problem, as the problem was obvious during the capturing of the lights ...
• capture software: Nina - autofocus

Now my questions:

• how come that only the center is focused?
• how come that away from the center stars are
  • out of focus
  • elongated
• Is this a focus problem?
• Is this a collimation problem?
• Is this a coma problem?
• Or is this a combination of all the before mentioned problems?

Any help really appreciated, as tonight and tomorrow night will perfect conditions over here!

AstroRookie

 

Edited February 1 by AstroRookie

[Adreneline]

So frustrating for you.

Looks like you could have a spacing issue - maybe:

Hope you get to make use of the clear skies tonight.

[AstroRookie]

58 minutes ago, Adreneline said:

So frustrating for you.

Looks like you could have a spacing issue - maybe:

Hope you get to make use of the clear skies tonight.

I'll check it out. Thanks!

[doublevodka]

Think @Adreneline has hit the nail on the head there

https://www.firstlightoptics.com/coma-correctors/baader-mark-iii-mpcc-coma-corrector-photographic.html

"Requires 55mm back focus."

Near the bottom of the product page here it shows you how to do it - https://www.touptekastro.com/products/touptek-atr3cmos26000kpa-imx571-colorful-astronomy-camera-26mp-1-8-aps-c-tec-cooling-deepsky-astronomical-telescope-camera

Alternatively, if you are in a rush and don't have time to sort it before the next imaging session, you could simply remove the MPCC from the equation, you'd still have some coma, but not as much as is showing with the spacing issue currently.

Hope that helps 👍

[AstroRookie]

51 minutes ago, doublevodka said:

Think @Adreneline has hit the nail on the head there

https://www.firstlightoptics.com/coma-correctors/baader-mark-iii-mpcc-coma-corrector-photographic.html

"Requires 55mm back focus."

Near the bottom of the product page here it shows you how to do it - https://www.touptekastro.com/products/touptek-atr3cmos26000kpa-imx571-colorful-astronomy-camera-26mp-1-8-aps-c-tec-cooling-deepsky-astronomical-telescope-camera

Alternatively, if you are in a rush and don't have time to sort it before the next imaging session, you could simply remove the MPCC from the equation, you'd still have some coma, but not as much as is showing with the spacing issue currently.

Hope that helps 👍

I've checked, and I think my error is that I did not take into account the 17mm sensor to flange distance; so I had 17+55 = 72mm. Corrected that, now it's a matter of waiting till it gets dark, because it will be ab excellent night: clearoutside's opinion

Thanks for your help!

[ollypenrice]

12 minutes ago, AstroRookie said:

I've checked, and I think my error is that I did not take into account the 17mm sensor to flange distance; so I had 17+55 = 72mm. Corrected that, now it's a matter of waiting till it gets dark, because it will be ab excellent night: clearoutside's opinion

Thanks for your help!

17mm is huge so you've probably cracked it. If using a filter, add 1/3 of the filter thickness to the backfocus. Filters are often 3mm thick so add 1mm.

Olly

[AstroRookie]

Still no go; if I use 37,5mm + 17,5mm from flange to the sensor, I cannot reach focus at all. Also after having read this thread I'm even more confused. Not using the coma corrector is not an option, as I cannot tighten the spacers in the focuser; did I purchase spacers with the wrong diameter ???

So too bad for this perfect nights - frustration is part of this hobby

Back to my dslr for now ...

 

 

Edited January 9 by AstroRookie

[Stefan73]

11 minutes ago, AstroRookie said:

Still no go; if I use 37,5mm + 17,5mm from flange to the sensor, I cannot reach focus at all. Also after having read this thread I'm even more confused. Not using the coma corrector is not an option, as I cannot tighten the spacers in the focuser; did I purchase spacers with the wrong diameter ???

It sounds like you should have a 37.5mm spacer between the camera and the coma corrector and then the coma corrector goes fully into the focus tube clamp; like a nose piece on a camera.  Is that what you have?   Can you see if you're getting close to focus at either full extension or full retraction of the focuser?

 

[AstroRookie]

1 hour ago, Stefan73 said:

It sounds like you should have a 37.5mm spacer between the camera and the coma corrector and then the coma corrector goes fully into the focus tube clamp; like a nose piece on a camera.  Is that what you have?   Can you see if you're getting close to focus at either full extension or full retraction of the focuser?

 

That is what I had this evening: a 37,5mm spacer between de camera and the coma corrector, then with this adapter it is screwed onto the focuser. But not even close to focus, not at full extension and not at full retraction, donuts stars ...

[alacant]

1 hour ago, AstroRookie said:

with this adapter it is screwed

Not enough information (a photo perhaps?) to say for certain, but something to try...

Lose that adapter. It is taking the sensor too far away from the tube. Instead, push the camera-extension-cc  assembly into the focuser and secure using the  thumb screws 

The Baader cc needs 58mm from the shoulder of the m48 thread. We don't recommend using the Baader supplied M42 adapter. Use a -say 5mm- shorter extension and a proper 5mm M48 to m42 adapter at the camera end.

HTH

Edited January 9 by alacant

[Stefan73]

Definitely try what alacant suggests. 

The only thing I'd add is you can try focusing on something far away during daylight so you don't waste imaging time on faffing with extensions.  You might have to move the focus tube a bit further in when focusing on stars but it should give you a good starting point.  If it's still not working try to work out whether the camera is too near or too far.  It should be a bit more obvious if you're getting closer to focus when at maximum extension or minimum extension.

[AstroRookie]

Apparently I needed a 37,5mm space because that is what the MPCC requires when using a camere with T2 thread.

I tried that and it looks better but far from good. Attached 2 screenshots of a capture with Nina, one with the image  "fit-to-screen", the other 1:1. The stars look weird all over the image. Autofocus does no longer work (plate solving however went ok).

I checked my collimation, and that looks ok

Any idea what is causing this?

[Stefan73]

Sometimes you need a bit of experimentation with back spacing. The suggested value can be just a starting point.

Probably the best way to get more suggestions would be to post a fits of a short exposure sub of a good star field and a picture of the camera and coma corrector all connected up to the telescope.  It looks like the tails on the stars are all going the same way but hard to see.  Could it be tilt?  Have you looked at a sub with astap or siril's tilt detector?

 

[Adam J]

13 hours ago, AstroRookie said:

Apparently I needed a 37,5mm space because that is what the MPCC requires when using a camere with T2 thread.

I tried that and it looks better but far from good. Attached 2 screenshots of a capture with Nina, one with the image  "fit-to-screen", the other 1:1. The stars look weird all over the image. Autofocus does no longer work (plate solving however went ok).

I checked my collimation, and that looks ok

Any idea what is causing this?

top one looks like a guiding error, maybe from the jump at the start of your guide graph? Either way it doesn't look like a camera or corrector spacing issue, it could also be collimation. 

[AstroRookie]

I think it might be a combination of tilt and collimation. Last summer I did an upgrade of my telescope, and had pinched optics. I loosened the screws a  bit too much I guess and as I mainly photographed around the zenith at that time I didn't realize it  that when the telescope is pointed a little (30°) above the horizon, the collimation is completely lost. Just tried to correct that by tightening a bit with the "business card" method.

Next session I will try to inspect eventual tilt - thanks for the tip. But I think that at least the focus problem is solved. Unfortunately no clear nights according to clearoutside.com for the coming days to check it out.

[AstroRookie]

So I got my collimation right. I took a picture of 5s in park position (no screenshot, you'll have to take my word), ran an auto-focus and all looked well.

Then I started my sequence on the Rosette Nebula and got a warning after the focus routine (10s shots) and I interrupted it. The last picture taken during the focus routine shows very weird looking stars. To me it at first it looked like a guiding problem, but judging the graph my guiding looked pretty good.

As in the upper left corner I don't see vignetting (normally I have vignetting in all 4 corners of the ilmage), could it be that my focuser (I'm using the Orion 8" astrograph stock focuser) flexed?

Edited February 1 by AstroRookie