Quote:
Originally Posted by barx1963
Coma is an aberation that is inherent in newtonian telescopes. It results in stars towards the edge of the field starting to look like little comets with tails pointing outward. In a correctly collimated newt, the centre of the image where coma is not present is central in the focuser, so stars and objects that you are looking at are not affected, but stars near the edge are. Hence for visual use it is less important ( at least I think so) as I am only really looking at the object in the centre but when imaging it can make an image less appealing. For planetary imaging, the object of interest is usually in the middle anyways so coma can be less of a factor there.
Newts with faster focal ratios (f5 and faster, eg f4) have a smaller coma free area, which is why you hear people say that fast scopes are less tolerant of poor collimation.
Moving the mirror is often not that complicated. the cell that it sits in rides on (usually) 3 bolts and some springs. Simply replacing them with longer bolts and strings can often do the job.
Malcolm
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Oh wow i never you could get longer bolts and put it in to make it closer to the secondary mirror and eyepiece. But don't some dobs have fixed primary mirrors.
And now i know what coma is. Thanks for telling me. Such nice people on here.
