First light ASI2600MC- Spacing? Tilt? Something else?

[Icesheet]

I recently had first light with my new  ASI2600MC on an Esprit 100. In terms of the sensor itself I think I’ll be very happy. The data was extremely clean. It basically didn’t need any noise reduction. However, it is also the worst I’ve seen stars on the Esprit.

 

Can anyone comment on what I’m seeing here. Is this tilt, spacing or a combination of both? It was also the first time using a ZWO EAF and OAG so that may complicate things. The OAG in particular was causing vignetting at the top of the image. Flats sorted it but it now appears to have introduced some diffraction on the stars. Could it do that?

I know I’ll have to do some investigating but hoping someone can point me down the right path before I go down the rabbit hole!

[steppenwolf]

1 hour ago, Icesheet said:

The OAG in particular was causing vignetting at the top of the image. Flats sorted it but it now appears to have introduced some diffraction on the stars. Could it do that?

If the OAG protrudes into the light path, the machined edges of the prism support could easily cause diffraction artefacts - can you adjust the prism outwards?

[Icesheet]

15 minutes ago, steppenwolf said:

If the OAG protrudes into the light path, the machined edges of the prism support could easily cause diffraction artefacts - can you adjust the prism outwards?

I suspect and had an inkling it might be something like that. I pretty much just screwed it in place but I assume there must be some way to adjust it. Hopefully that should be a fairly straight forward fix. Thanks!

[steppenwolf]

10 hours ago, Icesheet said:

I pretty much just screwed it in place but I assume there must be some way to adjust it. Hopefully that should be a fairly straight forward fix. Thanks!

Normally that is the case. Also try to get it aligned on the long edge of your sensor as this further also helps as it limits the protrusion into the light cone falling on the sensor.

[teoria_del_big_bang]

Star shapes aside that is still a great image 🙂 what is the total exposure time on it ?

Sorry I am no expert and cannot work it out but does not really look to be a spacing issue, to me.
Even a star near the centre is not really round.

But definitely elongated towards the corners below is bottom right,
 

But not like that in top left although stars still distorted, is that the diffraction you talk about causing that ?

I assume this is a stacked image ?
You may get a better idea looking at the individua raw frames.
What is the exposure on these frames ?

Steve

 

[Icesheet]

12 minutes ago, teoria_del_big_bang said:

Star shapes aside that is still a great image 🙂 what is the total exposure time on it ?

Sorry I am no expert and cannot work it out but does not really look to be a spacing issue, to me.
Even a star near the centre is not really round.

But definitely elongated towards the corners below is bottom right,
 

But not like that in top left although stars still distorted, is that the diffraction you talk about causing that ?

I assume this is a stacked image ?
You may get a better idea looking at the individua raw frames.
What is the exposure on these frames ?

Steve

 

Thanks 😊. Yes, were it not for the stars I’d be extremely happy. It is a stacked image 60x180sec for 3hrs worth of exposure. I realised the ‘final’ image might not be the best to analyse. When I get a chance at my computer I’m going to look at the individual frames. I have PixInsight and Im sure there are some scripts to analyse subframes. Maybe that throws up something. 
 

More elongation in one corner compared to another might suggest tilt then? Guiding was good so I don’t think it’s that.

The diffraction spikes I was talking about are like the one above. I’m fairly positive it’s the OAG for that now. 

Edited September 22, 2021 by Icesheet

[Icesheet]

Ok, managed to look at some subframes quickly before I run off to work. There's definitely something happening from right to left and more so to the bottom right like you observed Steve @teoria_del_big_bang. Here's the PixInsight maps. Can I conclude tilt from this?

 

[teoria_del_big_bang]

Like I say I am no expert as not long in the game but could be some slight tilt I guess, I think those cameras have some method of tilt adjust don't they ?
I tend to agree not guiding otherwise all stars would be distorted in a similar manner.
I have no experience with OSC or OAG's but never seen it where some stars seem to have the blue offset, like below.

Whether that indicates something to someone with more knowledge I am not sure.

I am sure somebody on SGL will be able to help more than my limited experience but keen to follow the thread as maybe I learn something as well.

That really is a nice image for not that much integration time, I guess you get some pretty dark skies where you are then that will really suit that OSC camera.
I almost bought the same but even with my mono camera LRGB imaging is rare for me with light pollution and it always seems for me that the few clear nights in north UK coinside with pretty full moon so decided not to go for it.

Steve 
 

 

I now see the diffraction spikes caused by the OAG ?

 

[Icesheet]

Yep, I’ll wait to see if anyone else can chime in. Thanks for your input. I noticed that too so I’m praying that would be an effect of tilt with light hitting the sensor obliquely. It is quite worrying that the ‘good’ side of the eccentricity isn’t great itself though. 
 

I think the diffraction is the OAG yes. It right in the zone where it vignetted so must be. 

Edited September 22, 2021 by Icesheet

[Icesheet]

45 minutes ago, teoria_del_big_bang said:

That really is a nice image for not that much integration time, I guess you get some pretty dark skies where you are then that will really suit that OSC camera.
I almost bought the same but even with my mono camera LRGB imaging is rare for me with light pollution and it always seems for me that the few clear nights in north UK coinside with pretty full moon so decided not to go for it.

Steve 

 

Sorry Steve just realised I didn’t respond to that. Yeah it’s dark enough but not as dark as I what have expected for a fairly isolated valley in Norway. Bortle 4 but closer to 5 than 3 I’d say. I actually just moved away from mono. Struggled to finish an image with nights getting clouded out then missing a filter etc. I picked up the L-extreme and whilst  mono would be preferable I’m hoping I won’t miss it too much with this sensor.

 

Chris

Edited September 22, 2021 by Icesheet