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View Full Version : Your opinion on this mirror

TimmySand
13-March-2009, 04:20 PM
Its an 8 inch mirror on ebay for 80 bucks and the seller has good feedback, is there anything I am overlooking?

http://cgi.ebay.com/NEW-8-INCH-PRIMARY-PARABOLIC-TELESCOPE-MIRROR_W0QQitemZ270307640104QQcmdZViewItemQQptZTel escopes?hash=item270307640104&_trksid=p3286.c0.m14&_trkparms=72%3A1205|66%3A2|65%3A12|39%3A1|240%3A13 08|301%3A1|293%3A1|294%3A50

The f-ratio is actually 3.7, is that too low?
RickJ
13-March-2009, 08:36 PM
Seems to fall into the too good to be true category. Also a claim of quarter wave accuracy with nothing more is meaningless. Without knowing how this is measured and at what frequency it could signify a very lousy mirror yet meet their claim. Personally, I'd not buy any astro products from Ebay but stick to more mainstream sources.

Rick
redshifter
16-March-2009, 01:53 AM
On the listing, it says 'Power = 6'. What does that mean?
RickJ
16-March-2009, 03:41 AM
I took that as a clue to run. Makes no sense to me either. Shaving mirror magnification?

Rick
Siguy
16-March-2009, 04:26 PM
Those mirrors are a scam, they're ~f/3 spherical mirrors and very thin, too. I'd stay away.
HypothesisTesting
17-March-2009, 04:51 PM
Its an 8 inch mirror on ebay for 80 bucks and the seller has good feedback, is there anything I am overlooking?

http://cgi.ebay.com/NEW-8-INCH-PRIMARY-PARABOLIC-TELESCOPE-MIRROR_W0QQitemZ270307640104QQcmdZViewItemQQptZTel escopes?hash=item270307640104&_trksid=p3286.c0.m14&_trkparms=72%3A1205|66%3A2|65%3A12|39%3A1|240%3A13 08|301%3A1|293%3A1|294%3A50

The f-ratio is actually 3.7, is that too low?

The cleanliness of mirror is important also. I got a 10 inch mirror in 1993, installed it on my school's telescope, and tried to keep it clean all these years. But I still have a lot of dirt on it I wish I could clean.

So it might not be clean enough, depending on its care and age