Secondary mirror size

[Sirius_Starseed]

If anyone read my last thread they'd know that I've gone and chipped my secondary, glued it back together (wasn't my idea) , and now it 'ghosts', so basically it's royally F'd up. So much for my £100 budget, this sure is turning out to be an expensive hobby.

Anyway, I now need a new secondary. My 130P takes a 1.4" secondary mirror but I'm wondering what are the pros/cons of getting a bigger mirror? I've seen a 2" on Astroboot. Would this help or hinder my viewing or should I just stick with the same size i.e. 1.4"? Also, the 2" on Astroboot is from a Star Diagonal and it's a slightly different shape (flat?) does this matter or do I have to buy an elliptical like the same as the one I've just messed up? There's another Star Diagonal on Astroboot but it's a 1.25". Again, what are the pros/cons of getting a smaller mirror?

Thanks!

[brianb]

Optics Eliptical Flats Page

Better bigger than smaller. The HiLux coatings are worthwhile, they last much longer as well as performing better.

[Sirius_Starseed]

Optics Eliptical Flats Page

Better bigger than smaller. The HiLux coatings are worthwhile, they last much longer as well as performing better.

That's excellent! Thank you.

I honestly thought secondarys would be much easier to locate. Not many sites seem to sell them. Maybe people don't have stupid accidents like me lol.

[haitch]

The one off astroboot would probably incur additional secondary shadow and if it is a greatly different thickness you may have difficulty aligning it with the focuser.

That said if a new direct replacment is a cost you can't afford at the moment it should at least get your scope working again.

Mind you they don't look too cheap. If you really want cheap you could always buy one of their cheapo diagonals for about £3 and take the mirror out of that (the back comes off with 4 screws). The shape may lead to a bit of extra diffraction but it's a damn cheap way of getting the scope working again.

Oh, and another supplier for mirrors...

telescope diagonal secondary mirrors

[michael.h.f.wilkinson]

Bigger is better if you want to go wide field, but bigger is NOT better if you want better resolution and contrast on planets. Unless you were experiencing vignetting in you widest FOV eyepieces (visible loss of light in objects as they move to the edge of the field) I would NOT go for a bigger one than was installed!