flat part to secondary mirror

[colesmat]

Hi folks. I'm in the process of collimating my skyliner 200p that i got a couple of weeks ago and when viewing the secondary mirror through the focuser with no ep attached, I can see that at the bottom of the mirror there is a slight flat edge. It is definately the shape of the mirror and not just the angle of it as it's the same at any angle that i tilt the secondary. Has anyone else had this? Will it affect viewing?

[ronin]

From memory this is not the first I have read of this. It would seem that quite a few have a small flat section, think one or two have been reported with a bevelled edge. The mirrors are made oversize in any case and I would suspect they have a reasonable amount of "spare" area. So nothing that would impinge on the viewing unless the secondary was really a long way off.

[NGC 1502]

At first I thought that the 'flat edge' you mention was poor collimation and a reflection of part of the tube wall and the end of the focuser draw tube (pic 3 on the right)

But from your description - " It is definitely the shape of the mirror.....etc" I really wouldn't worry, the extreme edges of the secondary are often not used as the light cone from the primary is usually a bit smaller the the secondary mirror.

If it were me, I'd collimate and enjoy the views.

Regards, Ed.

[Daniel-K]

sont worry i think all SW have this mine has it too, its just were they hold the mirror for coating

[colesmat]

Thanks for the replies. Its good to know that it shouldn't affect viewing but it doesn't half make it hard to adjust so it's circular through the cheshire! Its almost like guesswork.

[colesmat]

Ed, that's what I first presumed but the view on all the pics are with the tube blocked off with a piece of paper. Should have been clearer in my description.

[Jason D]

The mirrors are made oversize in any case and I would suspect they have a reasonable amount of "spare" area. So nothing that would impinge on the viewing unless the secondary was really a long way off.

I really wouldn't worry, the extreme edges of the secondary are often not used as the light cone from the primary is usually a bit smaller the the secondary mirror.

Not entirely true. Check the following post

http://stargazerslou...20#entry1756603

Jason