Image of the day

Captured by
Craig Bobchin

Coathanger CR 399

My Account

New to Astromart?

Register an account...

Need Help?

Does a thin, 8" mirror need central support?

Started by toml, 01/04/2003 03:59PM
Posted 01/04/2003 03:59PM Opening Post
I have an 8" dob with a thin Taiwanese mirror in it. The cell supports the mirror on its perimeter with clips. The mirror cannot shift or fall our in any way, and holds collimation really well.

But the whole back of the mirror is exposed, with no central support. I have a metal plate that would perfectly and snugly fit in the OTAs rear ring, and can be and thought if I put three felt pads near the center of that plate, that those could add some support to the center of the mirror.

I don't SEE anything resembling distortion due to sagging, and wonder if sagging could even be a real issue with thin 8" mirrors. Real or imagined, should I go through with this 10 second modification?

TomL
Posted 01/05/2003 06:31AM #1
Tom
I'm a believer in "if it ain't broke don't fix it".Besides, an exposed mirror will acclimate faster and a metal plate ,lossing heat behind it, may worsen its performance.
$.02 worth Bob

Fujinon 10x70 FMT-SX binocs
Tak FS-78 ƒ/8.1 - 630mm fl.
6" ƒ/6.5 homeground newt. - 981mm fl.
10" ƒ/4.85 homeground dob. - 1231mm fl.