I have a problem, and its driving me crazy

[Flip Andreas]

Ok, so here's the deal, i got my stuff set up. but there is something funky with my stars, I cant really put my finger on whats going on and i need some more experianced eyes to help me figure it out. 

First i thought maby my focuser is tilted, but i'm not sure exactly how that would look.

But just now found this spacing guide picture, and.. is that it?

In this picture i'm using the following:

Scope: TS-Optics Photoline 80/480mm Triplet Apo

             Scope has a 1x field flattener

Mount: Sky-Watcher EQ6-R Pro

             Guiding at RA 0.60"ish | Dec 0.50"ish

Camera: ZWO ASI294MC Pro

Picture exposure: 300sec @ 120Gain

 

Here is a 1 picture from the other night and as you can see my stars are not right. 

 

i stumbeled on this gem and thought, is that it?

 

 

I hope you all have had a great summer!

BR

Flip

Edited August 24, 2022 by Flip Andreas

[Carastro]

I had to blow your image up quite a lot to see any problem at all.  I am not the greatest at technical stuff but looks like a slight amount of tilt as the bottom corners are slightly elongated. 

 

See what others say.

 

Carole 

[TerryMcK]

I’m struggling to see anything wrong with the image as posted. There are a couple of stars that are blown out and are probably binaries creating slight elliptical shapes but not in the same direction so tracking is ok.

I think it is ok.

[Flip Andreas]

2 hours ago, TerryMcK said:

I’m struggling to see anything wrong with the image as posted. There are a couple of stars that are blown out and are probably binaries creating slight elliptical shapes but not in the same direction so tracking is ok.

I think it is ok.

Yeah, i think my exposures are too long as well. I'm going to try some shorter ones to see if it helps.
But this is what i'm thinking of, its easier to see on the faint stars, they look like small lines, This is at the bottom right hand side of the picture. Top left looks opposite. at least thats what i think. heh

 

3 hours ago, Carastro said:

I had to blow your image up quite a lot to see any problem at all.  I am not the greatest at technical stuff but looks like a slight amount of tilt as the bottom corners are slightly elongated. 

 

See what others say.

 

Carole 

yeah, its hard to see, but its enough for me to feel the need to figure it out. 😃
I had a chat with a friend of mine that does a lot of photography and he also leans against it being a backspacing issue. 
But looking at the whole picture it looks like it might be a small tilt too. 
I'll try to sort one thing at a time and look in to the backspacing first. 
If i need to fix focuser tilt I'm not sure how to get that done right. I think i need a laser pointer of some sort(?) hehe

Edited August 24, 2022 by Flip Andreas
spelling

[TerryMcK]

Now you have blown the image up I can see it. It will be a minuscule amount of tilt at that corner and it is too close to the sensor. This isn’t a focuser problem but the back focus distance from the sensor to the rear element of the flattener at that corner. So a shim may be all it needs. When I was in engineering we used to use a tiny bit of newspaper which was 1.5 thousandths of an inch thick (0.04 mm) and newspaper is incompressible so remains the same thickness with the relatively low forces applied. 

You would have to do trial and error experimenting with more than one piece of paper until you get it right unfortunately.

 

Another alternative option is to use the ZWO tilt adapter which I use on my solar scopes to minimize newton rings when imaging the sun. The adapter uses tiny grub screws that are adjusted by allen key to dial in tilt of the sensor relative to the rear element precisely. Make sure you get the right one for the ASI294 as they do make different ones.

 

Finding which corner has the issue is another matter and you sometimes end up chasing your tail trying to find out where to adjust so take your time and don’t worry about losing  a valuable night of imaging whilst adjusting the camera - there will be many more.

[Flip Andreas]

 

23 hours ago, TerryMcK said:

Finding which corner has the issue is another matter and you sometimes end up chasing your tail trying to find out where to adjust so take your time and don’t worry about losing  a valuable night of imaging whilst adjusting the camera - there will be many more.

 

It's troughout the whole picture, i just blew up a part of it for easy viewing 😃
It looks a lot like the Camera sensor too close illustration, but its not even, so i'm guessing there might be some tilt too

I have a few shims and can make some DIY i need be.
I'll look in to the ZWO tilt adapter too.

 

Setting things up, tearing it down figuring out how to do things and solving issues is half the fun to me.

 

For testing I can even use a farm on a small montain across the lake to see if i get things right.
It's enough of a distance so the lights on their house and barn can be used to get a pretty good focus. it's a bit of a pain to target at that distance, but i can play around even on cloudy nights =D

It helps to talk to someone with experiance to figure things out, and maybe get a sanity check, hehe

[TerryMcK]

If it is all over the image then yes experiment with overall shimming. There are normally some thin shims in the box that the ZWO cameras come in.