Focus Help

steve000 (Steve) · #1 27-01-2011, 01:29 PM

Gday all,

Over the last 2 weeks, making the most of the clear skys I have been practising imaging with my 6' scope and webcam from morgans last year.

One common thing I have found is the inability to get good focus expecially on saturn. In every instance the scope has stabilized to the outside temperature and i have adjusted the focus as fine as I can but still cant get focus. I believe the collimation is ok however I do need to check this. Apart from that any ideas?
Equipment is Saxon 6" newt on Eq3, SPC880 flashed to SPC900NC with a celestron 2x barlow

Pics attached

jjjnettie (Jeanette) · #2 27-01-2011, 01:35 PM

Seeing is King when it comes to planetary imaging. And that is totally out of anyones control.
The more the stars twinkle in the night sky, the worse the seeing is.

floyd_2 (Dean) · #3 27-01-2011, 08:17 PM

Have you tried a Bahtinov focusing mask Steve?

Dean

RobF (Rob) · #4 27-01-2011, 09:08 PM

They look pretty good to me
Agreed seeing is a biggy, as is collimation. You need lots of good data and good processing skills.

Is the OTA definitely at equilibrium with air? (at least one hour outside).

steve000 (Steve) · #5 27-01-2011, 09:24 PM

Thanks for the positive comments.

Bahitnov focusing no not yet any basic guide on that?

I would say its equal to the air temp or verrrrrry close.. my scope lives in my garage that is reasonably well ventilated and is brick, I hardly notice a temperature difference going from inside to outside.

floyd_2 (Dean) · #6 27-01-2011, 10:32 PM

Perhaps a good set of collimation tools would be an excellent addition to your kit Steve. It's always best to be sure that your collimation is spot on before each session.

A Bahtinov mask fits over the end of your scope, and causes a particular pattern of diffraction spikes to show up in the eyepiece. As you reach perfect focus (usually on a brighter star) the diffraction pattern becomes symmetrical. It's a very easy way of achieving perfect focus.

I think there's a person on IIS who makes the masks. Also, you can get Astrozap ones known as Focusing Caps which double as lense caps (which I use), or make your own here.

Dean