Help! Is this coma or collimation?

[mark7331]

Hi all. I need a bit of help in working out exactly what this is. I've been imaging during the recent clear skies and my guiding has finally been great but I've noticed in the edges of the images the stars are elongated and pointing into the centre.

I'm not entirely sure if this is coma, poor collimation, both or something else... so any advice would be really appreciated.

My imaging scope is a newt and I've attached the top right and bottom left from one of my recent images so you can see what I mean.

Thanks in advance.

Mark

[Whippy]

I think an image with the whole field showing would help .

Tony..

[lukebl]

I'd say it was coma, especially if you're not using a coma corrector. But, as Tony has said, the whole image would help. A coma corrrector is essential with a fast Newtonian.

[Stephen]

Another vota for coma (but as above, whole image please?) - second hand corrector is less than £100 and makes a whole heap of difference

[mark7331]

Ok chaps here's the whole thing

Cheers

Mark

[Whippy]

Looks like coma to me as the stars spread out radially. Your collimation might be slightly out too as the stars at the top right looks slightly worse than the ones on the left.

Tony..

[mark7331]

Thanks for looking guys. I've had trouble with collimation and have found that my cheepo laser collimator is in need of collimation itself. Time to upgrade I guess.

I've had a look on FLO for coma correctors but they seem to be aimed at DSLRs. Are they all suitable for CCDs and will I need adaptors?

Sorry..so many questions.

Thanks for your help.

Mark

[Whippy]

Coma correctors can be used visually as well as for imaging, they'll work on any camera (or eyeball), including yours. I guess their advertising is aimed at DSLR users as the chip is that much bigger so the effect is greater. You'll almost certainly need adapters and spacers as the spacing has to be pretty excact much like reducer/flatteners. I'd check the threads on your camera/filterwheel and take it from there.

Tony..

[Stephen]

Thanks for looking guys. I've had trouble with collimation and have found that my cheepo laser collimator is in need of collimation itself. Time to upgrade I guess.

I've had a look on FLO for coma correctors but they seem to be aimed at DSLRs. Are they all suitable for CCDs and will I need adaptors?

Sorry..so many questions.

Thanks for your help.

Mark

Your collimator should have three little grub screws - put it in some form of V shape to hold it level and you collimate the laser beam in much the same way as the scope I tend to check mine every other week or so and make a few small adjustments.

Re : Adaptors, my set up goes like this.

314L (13mm) - gender changer (t-thread, adds about 3-4mm) - filter wheel (21mm) - 15mm t-spacer - corrector (with 2mm spacer on it.)

This gives me the correct 55mm spacing distance.

[mark7331]

Tony, Kh3ldar thanks for that information. It's all getting clearer.

Cheers

Mark

[lukebl]

Despite the lack of a Coma Corrector, that's still a lovely M42, by the way!

[Black Knight]

Despite the lack of a Coma Corrector, that's still a lovely M42, by the way!

Yes, I agree!

[Stephen]

Despite the lack of a Coma Corrector, that's still a lovely M42, by the way!

Absolutely *really forget my manners some times lol*

[mark7331]

Thanks chaps! You're too kind!