M57 - Autoguided!!

Nice work there Dave. But tell me, some of the stars show colouration. I presume that this is not natural, yet you got good colour from the nebula - what caused the colouring in the stars?

Seanie.

Seanie, I'd say that is the result of the LPR. Considering the filter applies to all incoming light equally its fair to say that even though the colours may be not entirely true, they are natural insofar as the different colour stars do in fact have to have a different spectra.

Sounds like a good explanation to me!

Dave,
Just a couple of question on autoguiding:

1) What ratio of focal lengths is recommended for the autoguiding telescope to be in comparison to the main scope for the autoguiding procedure to work correctly/accurately?

2) How close to the "real" target does the "tracking" star need to be? i.e., can you track on say Arcturus, but take a photo of M57?

Thanks,

Michael,

The focal lenght of the guide scope is not critical many people advocate guiding at very long focal lenghts others get quite satisfactory results with 500 mm or so. Remember if you have a short scope you can always barlow it anyway. I'd recommend guiding at longer than 1000mm for a standard newt or SCT. Remember the idea is to get tolerance within about two arcseconds. I have found with my guidescope (5"mak f=1500mm) and my 9.25" SCT f=2350mm that this is easily acheivable.

Question two. The proximity to the target is not overly critical however it is critical that they be at the same approximate altitude so that differential atmospheric refraction doesnt cause false corrections to be sent to the mount. I have never found a problem finding a guidestar within a degree or so of the target but I would have no problem going up to 5 deg away at the same altitude. Flexure between the guidescope and the main scope will be your biggest enemy and as I found last night the dreaded wind!

Dave,
Good stuff! Thanks for that!