What is this?

[Stu Wilson]

Ive downloaded ASTAP and uploaded a recent image of M42 with some weird artifacts going on.

Ie i was thinking spacing was out between my coma corrector and camera.

I dont know what all the figures mean that i looking at on the attached screen grab.

If anyone can help.

cheers

 

Stu

[ONIKKINEN]

HFD - Half flux diameter is a unit that measures the size of your stars in the image (in pixels in this case, to convert to arcseconds you need to know your pixel scale). Tilt measures the difference in star sizes between different areas of the image. Then the rather self explanatory number of stars detetcted, and used in the calculations and lastly off-axis aberration which i think means how much things like coma, field curvature, backspacing etc affect the typical star size.

Your tilt is pretty bad at 32% difference between different sides of the image indicating some collimation issues in either your mirrors or in your focuser and imaging train, mechanical issues with the tube/tube rings/other mechanical parts flexing or what is common in newtonians = a mix of all of them.

But another issue is that there are only 104 stars used for the calculation which seems really low. Its low enough that there is severe bias in the measurements, as you can see with most of the stars being on one side of the image and the other side is mostly dark. So is it that you really have issues in the imaging train or is it that the measurement is incomplete?

Anyway, thats what all of that means. For CC to camera distance evaluation you need to have the scope fairly well collimated and most sources of tilt eliminated or you will have a tough time getting the correct distance. And for the actual evaluation itself you might find the aberration inspector tool more convenient.

[Stu Wilson]

ok thanks for reply. i put together my adapter rings from cc to camera for spacing and i think ive found the issue...... ie leaning tower of piza.

Has anyone else used these rings before where you get 4 to 10mm or whatever it is and remove and add whichever makes up your required BF? and found them to tilt?

 

Cheers

 

Stu