What's going on here?

[Sabalias]

Hi All,

Last night was the first clear night in weeks and my second chance to use my ED80.  I'd previously set marks for my tripod (using a proper compass instead of my phone) and I was delighted when I came to polar aligning and found Polaris sitting almost in the middle of my polar scope - saved so much time 🙂. I realised that I would have problems with dew (I have yet to purchase a dew heater but I have one on my Christmas list) but I thought I'd try a bit a imaging to keep my hand in and see what came up. Anyway, can anyone give me an idea of what is going on with the image below please (cropped from the centre of an original)? I'm wondering if it's one of the following:

• Recently installed an IDAS LPS-D3 filter
• Dew
• Focus (I thought it was all good but I guess I may have knocked it out)
• Bad guiding 

I'm really hoping there's nothing wrong with the scope and field flattener which performed fine a month or so ago.

 

Many thanks,

Stu

[Elp]

Initially I would say the focus is off. Did you use a bahtinov mask to tune focus? If you haven't got one it's essential for astrophotography and they're cheap.

[Clarkey]

From the 'smeared' look of the star shapes - almost like coma - I would suggest something in the image train is out of alignment. It may also be a focus issue too. I assume the whole image looks like this? It is a bit odd that an ED80 is giving a red colour.

I would suggest setting everything up in daylight and check it then. Much easier than fault finding at night.

[Sabalias]

43 minutes ago, Elp said:

Initially I would say the focus is off. Did you use a bahtinov mask to tune focus? If you haven't got one it's essential for astrophotography and they're cheap.

Yep, I have a mask and the focus was fine-tuned but it's possible that I knocked the focus off before I started imaging. I'm not really familiar with refractor telescopes so was a bit confused; if it is focus then it's user error and an easy fix 😄

[Sabalias]

36 minutes ago, Clarkey said:

From the 'smeared' look of the star shapes - almost like coma - I would suggest something in the image train is out of alignment. It may also be a focus issue too. I assume the whole image looks like this? It is a bit odd that an ED80 is giving a red colour.

I would suggest setting everything up in daylight and check it then. Much easier than fault finding at night.

Yes, it's the whole image. I was wondering if the filter might be causing the red colouring or, perhaps light refraction caused by dew......

[ONIKKINEN]

Focus is off, stars are hollow donuts. Since this is the center of your shot and stars are misshapen its a good idea to check your guiding. If your stars are misshapen only in the corners, that would mean backfocus issues.

[Tim]

Is the image from the exact centre of the frame? The poor focus emphasizes the issue of the misshapen stars, which may have several causes, including inherent coma, focuser slop, camera tilt, or poorly collimated objective.  See if you can post a full frame picture, it will reveal a lot more.

Tim

[rickwayne]

Definitely a focus issue. I plate-solved the image and the eccentricity matches neither the RA nor the DEC axis, so it's probably not guiding (although if you have problems in more than one axis, it's possible to have non-axial ovals).

[Elp]

It is more than a focus issue as the stars are not concentric, it looks like they have moved top left as it were from some sort of movement or non movement whilst guiding or some tilt. As Tim has suggested a full image uploaded may provide more insight.

Also how/where is the IDAS mounted within your imaging train?

[rickwayne]

Yes, but there is certainly a focus issue going on, as ONIKKENEN notes.

[Sabalias]

Hi everyone,

Thanks for the responses so far. This is the full frame.

Regards,

Stu

[Sabalias]

9 hours ago, Elp said:

It is more than a focus issue as the stars are not concentric, it looks like they have moved top left as it were from some sort of movement or non movement whilst guiding or some tilt. As Tim has suggested a full image uploaded may provide more insight.

Also how/where is the IDAS mounted within your imaging train?

The IDAS is mounted in the camera body, between the mirror and the FF/Reducer on it's camera mount.

Stu 

[michael8554]

Hard to judge with the low res full frame you posted.

But overall focus is off.

And there's tilt, the right side of the image has stars almost round, the left side has coma.

Michael