Newtonian weird stars

[orly_andico]

I just did first light on my (new to me) AT8IN.

Check out this single 10-second sub: https://dl.dropboxusercontent.com/u/634 ... Y8-10s.jpg

it is 10 seconds so tracking etc. should not be an issue.

Stars are weirdly shaped across the field. It doesn't look like coma (well some areas have coma and some do not).

My question for the experts - is this solely due to bad collimation? (I used a Kodak film can!) or is the focuser sagging and causing the sensor to be tilted? (I hate that)

[beginner]

I am no expert.
Can it be due to pinched optic in addition to field not flat.

[kimo]

I ever encounted such problem and i didn't like it at all. all are diamond shape star, its collimation problem. how you collimate it, still very very hard to get round nice star with F/5 or lower f newtonian.

[kimo]

Hi orly,

Here is 5.39min H-alpha single sub with 6" newtonian F/5. no coma corrector.

thanks
Kimo

[orly_andico]

for me, mis-collimation and mis-focus is aggravated because i'm at f/3.0

collimation only by eye. waiting for laser colli to arrive.

[kimo]

laser collimator will be no use for astrophotography collimation. i had it before and i never used it.

1: do both optics aligment with just dot on EP cap and place one large gray paper under secondary ,day time alignment--works perfect
2: collimate with ccd and reducer.

first start from large round star on ccd "out focus" and collimate secondary, gradually reduce star size and keeps on collimateing (now require very fine adjustment) until you are satsfied.

i think you have another problem is that your CCD camera may not give you good result as it is color.
QHY8. HA- 25%, SII 25%, OIII 75%, HB 75%. will require long axposure on HA and SII.

[orly_andico]

Yes I know the OSC is less sensitive. That's why I'm running the OTA at f/3.