Coma along diagonal with APO refractor

[inFINNity Deck]

Dear forum members,

today I had first light with a new APO in my set-up. It has a flattener and I have been tinkering with spacers to get the distance between my ASI1600MM Pro Cool and the flattener. If I look at the stars in the lower left and upper right corners I am pretty satisfied, but not when looking at the other two corners. It appears that along the diagonal all goes well, but I would expect coma to show in all four corners when it is a matter of chip-flattener spacing. Also when having tilt, I would not expect the stars be fine along one of the diagonals (but I could be wrong there).

Any suggestions to the cause of this are much appreciated.

Thanks in advance!

Nicolàs

 

[inFINNity Deck]

Just wondering: Could tilt or collimation be the cause of this?

Nicolàs

[michael8554]

Is that a single sub or a stack ?

I see elongation in the same direction everywhere in your image.

Guide Error ?

Take a single short exposure to eliminate this, and stretch it to brighten the stars.

Michael

[inFINNity Deck]

Hi Michael,

Thanks for your response. This is a stack, but all individual subs show it. When I was testing the flattener-camera spacing I took 5 to 20 seconds subs to check the corners. The stack shown here is the result of 20 x 30s lum, 10 x 60s R, G, and B.

Unlikely to be a guide error as the central stars are round. Also it is mounted on a 10Micron GM3000HPS with a PAE of 5 arc-seconds, so I do not expect field rotation (nor guide errors). Normally I image with a SkyWatcher Esprit 150ED without much problems, do not even use a guide scope.

Nicolàs