collimating an sct

[rowan46]

I can't seem to get my nexstar 5 collimated to my liking. I appear to be getting concentric diffraction rings but whenever I try to image with my neximage jupiter is just a blob and looking closer at stars they are not quite pinpoints. I think my eyesight is failing a little as I can't seem to get it any better. I came across this mask while trawling the net and wondered if anybody knew of a generator for a 5 inch version Duncan's Decorating and Repair Services

[barkis]

If you wear spectacles to aid you for distance seeing, ie for driving etc., then you should wear them when focusing your scope. Doing so without them, can make the Image you view in the camera viewfinder seem focused to your eye, but will come out on the Image defocused.

Can you get a sharp focus whilst using an eyepiece on a star.?

If not, it could be temperature differential. Your optics have to be allowed to reach ambient temperature, otherwise stars might appear blobby, and detail on the moon for example could appear blurry.

Do you use your camera at the scopes prime focus?

If a star test is showing the diffraction rings to be concentric, then the collimation should be fine. If the mirror hasn't cooled sufficiently, the rings won't be very distinct either.

Ron.

[barkis]

Thre are suppliers of focusing masks. The are called Bahtinov Masks, and you need to supply the focal length of the scope, the diameter of the front corrector, the actual glass diameter, the outside diameter of the the scopes tube, and the diameter of the central obstruction, ie, the secondary holder.

Instructions as to using it will be supplied with the mask.

Ron.

[beamish]

Umm that's an interesting developmentre the mask ! Certainly makes collimation less worrying if it indeed works !

[barkis]

Umm that's an interesting developmentre the mask ! Certainly makes collimation less worrying if it indeed works !

Whoops!, I took the wrong fork . Silly me.

But, focusing was part of the Issue Karlo.

[rowan46]

My problems could be due to anything to be honest, it could be poor optics its an old scope with poor eyepieces, but it seems to have cleaner views on low power so i suspect its a collimation issue. The mask I saw has three cutouts in line with the collimating knobs which come together to form a pattern in the middle of the scope when properly when properly collimated. It apparently doesn't require perfect seeing so I figured with the moon around at the moment now would be a good time to practice my collimating. Does this mask ring a bell with anyone has anyone used it on this forum. I have seen a couple of references to it on cloudy nights and orphington astro