Saturn 20th May

[von Tom (Tom)]

I took delivery of a 5x Powermate with T2 adapter a couple of days ago and did this image of Saturn in average to poor seeing using the Canon 550D and 5x Powermate at prime focus of a 12" Sky-Watcher Dobsonian, best 1000 out of 7000 frames at 60 fps, 640x480 video crop mode, ISO1600 1/60sec exposures. Fairly overprocessed. The rings may be blurred due to field rotation as Saturn was near the meridian.


Thanks for looking,

Tom

[renormalised (Carl)]

Nice shot Tom

Have you got a bahtinov mask at all??. Might pay to grab one so you can focus your scope precisely. Might help with getting even crisper piccies.

[von Tom (Tom)]

Hi Carl

I am not too familiar with the use of bahtinov masks as I use the live view on the 550D. Does focussing with the mask depend upon seeing conditions? I don't think the image could have been much sharper given the seeing and the field rotation.

Cheers,

Tom

[renormalised (Carl)]

Originally Posted by von Tom

Hi Carl

I am not too familiar with the use of bahtinov masks as I use the live view on the 550D. Does focussing with the mask depend upon seeing conditions? I don't think the image could have been much sharper given the seeing and the field rotation.

Cheers,

Tom

The bahtinov mask produces a spiked star like point when you use it to focus on an object. When you move in and out of focus, those spikes (diffraction spikes) move in relation to where you are in the focus. The object of the exercise is to get a well aligned middle spike. When it appear in the centre of the star, your focus is good. Use it on a bright star to focus, then slew to your planet you're imaging. You may need to give it a little tweak when you get the planet in FoV. Your seeing conditions will affect your ability to focus, no matter what you use. But the mask will improve what you can get, without the mask.

It will help with your planetary images.

http://en.wikipedia.org/wiki/Bahtinov_mask

[asimov (John)]

Focus is spot on. Keep doing it the way you are. As you say, there is a possibility that field rotation is coming into the equation here.

I don't know how good the derotate feature is in Registax6 but it might be worth a look..

[Shiraz (Ray)]

Hi Tom. Looks like the new Powermate is a worthwhile investment - good image. Regards Ray

[Clayton]

Originally Posted by Shiraz

Hi Tom. Looks like the new Powermate is a worthwhile investment - good image. Regards Ray

I agree Tom, and I think good focusing is best done with a trained eye (call me old fashioned if you like ) but I believe that is the way that all of the most highly regarded do it Although to be fair I have never tried a mask as to work well I believe they need a bright point source which I could never achieve and slew back to a planet without disturbing the camera.