Quote:
Originally posted by rumples riot
Great image Bird, how on earth do you get shots that clear and how do you focus on a screen that can give false readings of sharp. You are amazing. Can you please help me with some focusing tips. I am now using a parfocal EP with the LPI which is helping and checking this with a hartman mask. Anything else you can help with?
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Well, like many things, having the right tool for the job makes some things very easy...
During the Mars opposition of 2003 I started getting back into astronomy after a break of about 15 years, and I had a manual focusser (JMI low profile) which was a real beast to work with. I started wishing for a motorized focusser.
I saved my pennies and eventually (about a year later) bought the JMI DX1M motorized focusser. It can set its position to a precision of 0.02mm, and is controlled by either a hand unit or serial cable to a PC.
JMI at first didn't want to give me the serial port control codes, but they relented after I asked nicely enough :-) So now I have written a Perl module that can control the focusser, so I can stay at my laptop and use arrow keys etc to shift focus position. Trust me, that makes a big difference.
Experience with this has shown me a couple of things:
* At f/6 you have to focus to within 0.05mm to get a sharp image. IF you have a faster scope then it is harder still.
* The focus position changes as Jupiter rises and/or the equipment cools down and everything shrinks a little bit. I have to shift the focus by 0.02mm or so every 15 minutes to stay in the zone.
* The 3 colours come to focus at different positions - about 0.1mm apart - so the only way to get a really sharp focus is to capture each colour seperately with a monochrome camera. I think this is due to atmospheric refraction effects. and the barlow.
I've integrated it with my filter wheel, so that I can "set" a focus position for each colour, and the laptop resets the focus position whenever I turn the wheel to shift filters (wheel also controlled by serial port).
BUT the most important thing is to have steady seeing, or else Jupiter is just a blurry blob and you have no way to know where the right position should be. So number 1 is to find good seeing location and conditions.
You can also try focussing on a nearby star before going across to Jupiter. There's a nice bright star nearby at the moment.
regards, Bird