Star Issues

[Killie]

I am sure this type of question has been asked multiple times but I was hoping someone could give me some advice here.

I have started trying to take images of 5 minutes and over using guiding but I seem to have an issue with my stars and I am hoping someone might be able to tell what the problem is. I thought it was just my focus but I bought a Bahtinov mask and I still seem to have the same issues. 

I suspect I am just not polar aligned/guiding properly but I wanted to check as this doesn't look exactly the same as most of the other elongated stars I have seen around the place but that could just be how it is affecting me or I may have missed similar examples to what I have happening here.

[MarsG76]

Most likely your polar alignment is out slightly and... you're using a guide scope? if so than the guiding is causing this because your guide star is too far away from the imaged object causing your imaged camera to move in a different arc.

The other possibility is that there might be mirror flop.... a OAG fixed this problem for me.

[Thalestris24]

Hi Killie

Was that image taken with an eq mount - it looks like maybe it was taken with an alt-az? If not, what guidescope were you using? What are unguided subs like?

Louise

[Killie]

It is a HEQ5.. 

I am just using a Skywatcher Finder Scope for guiding.. I am beginning to suspect it could be flex in the system when guiding as my old 90 second subs I used to take are much rounder etc. although i have added a field flattner and 2" IDAS LP filter as well since into my imaging train.

I also found that I think I need to get better at focusing as I did a test earlier and the stars were worse when I was using the mask as when I wasn't.

I think I need to basically strip the whole imaging train back to just the camera and add in different elements at 60s or so and see if things go wrong as I add things.

[Thalestris24]

Hi

I think you may have spacing issues with your field flattener (reducer?) and maybe also tilt. Sometimes you have to simplify things to find the causes of problems then add stuff back in the mix, one by one.

Louise

[Jannis]

For me it looks kind of similar to my images when not using a coma corrector (lower left corner) or when i'm using a faster lens. Are you using a coma corrector?

[sharkmelley]

Those are clearly optical aberrations.  You have a problem with optics - not with guiding.

Is that image the whole frame or is it a crop of one of the corners?  If it's a crop, can you show the whole frame.

Which scope are you using?  Which field flattener?

Mark

[Killie]

Using 80ED with the Skywatcher ED80 Reducer/Flattner

It is a crop.

I took some more images on Sunday night and will put the full image here from that which actually looks a bit better but still note sure it is right.

2nd image is one i took the night before, these are the jpgs straight from the camera.

1st image is 5 minutes and 2nd is 10 minutes.

Only other difference is that I manually focused without the mask for the 5 minutes sub as I could see straight away my subs with the mask were out of focus.

 

[Killie]

This is what I took at 90 seconds prior to using the Guider, Field Flattener & IDAS 2" LP Filter. It is after processing alas as I don't have the original RAWs or JPGs anymore.

It isn't perfect, the stars seem to be more or less round in this image. Unless someone with better analytical eye than me can see something I am missing.

I think I should perhaps try a 90sec sub again with the flattener and filter fitted to see if I have the same issues as the longer exposure images. Then perhaps I should remove them one at a time and see what I get. I think I would probably try and remove the filter first.

 

 

[Jannis]

Ouch, that's not looking good at all!

It looks like an optical issue, but hopefully someone else can point you in the right direction. First i would do though is to take 2 identical test images, both with and without the CC in place.
If it was a reflector i'd ask you to check collimation, but..

Edit: I see you just updated with a before image while i was typing. That image does look OK to me, and so i'd expect the scope itself to be good. I'd try without the CC first, then without the filter. If you're not using an OAG i can't imaging a guider could in any way affect the image other then with the tracking.

[Thalestris24]

Hi

I'd recommend taking some subs without the field flattener (think you'd need an extension tube in its place) just to eliminate it as a potential source of problems). I used to use a Bahtinov mask but now I use the focus tools in APT.

Louise

[Thalestris24]

3 minutes ago, Killie said:

This is what I took at 90 seconds prior to using the Guider, Field Flattener & IDAS 2" LP Filter. It is after processing alas as I don't have the original RAWs or JPGs anymore.

It isn't perfect, the stars seem to be more or less round in this image. Unless someone with better analytical eye than me can see something I am missing.

I think I should perhaps try a 90sec sub again with the flattener and filter fitted to see if I have the same issues as the longer exposure images. Then perhaps I should remove them one at a time and see what I get. I think I would probably try and remove the filter first.

 

 

That's pointing the finger at the field flattener and or filter.

[Killie]

So it has taken me a bit due to the weather sucking when I actually have a chance to get out.

Anyway.. I took a few images tonight with different set ups.

Basically it looks to me from these images that when I use the Field Flattner/Reducer or LP Filter apart I can get okay start but the moment I put them together in the optical train I end up with issues.

First Image is just a LP Filter, 2nd Image is just a Field Flattner/Reducer and final image is me using both again.