Tonight's Moon...

Hurr hurr hurr. Haven't touched an astronomical instrument other than S&T and Sky at Night (five months 'till I'm free!!!) since the first week of October. I thought things were busy in September!

I need some starlight. I'm starting to shrivel!

Michael, thats a really fine image. The focus looks great as does the exposure. You did a great job on the mosaic too there isnt a hint of the joins. Well done.

ALthough the focus isn't 100% perfect, I found the new focuser I bought very useful. Makes life alot easier. Thanks btw for your link previously to the shop in the uk (Ian King Imaging) which is selling the william optics gear - that's where I bought my sct focuser. It's a real pleasure to use.

One point worth noting about SCT and micro-focusers.

The SCT design produces the least possible errors (aberrations) when at prime focus. Moving the mirror either side of that position introduces errors.

What this means from a practical point of view is that the mirror should be moved to the prime focus position and then use the micro-focuser to get sharp focus.

This will ensure minimum aberrations and best possible field sharpness.

Next question, how do I do this?

Use a standard prime focus adapter and focus with the camera in place. Next replace with micro-focuser and get sharp focus. You should now be in the best possible focus with the setup.

You may notice that the prime focus adapters are all a standard length. This is to simulate a star-diagonal, which Celestron and Meade assume is in place when designing their scopes.

Later,

Jed.

Jed this is something which came up a while back on these boards and to me is a very interesting question.
After delving through the mapug archives and asking Qs on the lx200 yahoo groups, no one was able to state with any certainty where the focus point is.
The best guess was to focus the scope using standard equipment, i.e. focus using the supplied backend and diagonal like you say above (would you believe you cant use lx200 as is without a diagonal), this is the position that the designer expects you to use the scope.?!?
This is an assumption that I am not happy with, as I do not give them the benifit of the doubt.

I would VERY much prefer to know the exact position in mm from the back of the scope tube, but no one seems to know this location, short of spending tedious time with a ronchi tester or imaging (where seeing would affect results), I dont know of a way to derive it.

Michael - nice image. It might be my monitor but the image seems rather 'brown'. I usually image in B&W and it seems to give a more natural look to lunar images...

Michael - nice image. It might be my monitor but the image seems rather 'brown'. I usually image in B&W and it seems to give a more natural look to lunar images...

Dave,
Thanks for the feedback.
Something like this perhaps?


I originally left it in colour to reflect the slight colour one sees when observing the moon, especially if it is low in the sky.

I'd be really interested to know which image people here prefer - the original colour image or the black & white version above.

Regards,