Re: [ATM] ATM Edmund secondary mirrors - worth it?

[Mike Lockwood <melockwo@uiuc.edu>]

Gil, John,

I'm going to express some opinions here.  I'll probably get corrected, 
maybe reprimanded, but maybe someone will actually agree with me....

John Lynch wrote:
> I've had good luck with ProtoStar.  In addition, the
> Pyrex secondaries are certified to the accuracy stated
> ($75.00) and if you purchase the ULS Quartz ($137.50),
> they'll provide you with an analysis of the secondary
> (interferogram).  Both are, by the way, out of stock
> currently according to their website.

This is exactly why I've never had ANY luck with ProtoStar.  They are 
always out of the size I need!  Based on their customers' comments, 
though, they make excellent products, but they're a bit expensive in 
my opinion.

Ever since I started working on flats, diagonals are a bit less 
mysterious to me.  I think most modern diagonals from the likes of 
Protostar, AstroSystems, etc. are quite good.  Avoid the ones that are 
really cheap, unless you want to refigure them.  You definitely get 
what you pay for.  If you get a flat from a reputable place you'll 
probably be OK.

As far as the Quartz diagonals go, they will be more stable during 
temperature changes, but I think it would be very hard (if it is 
possible) to notice the difference due to the smoother surface.  The 
coating smoothness likely has a larger effect, it seems to me.

If you really want to improve the secondary mirror/support system, try 
a wire spider!  Reducing diffraction may result in a larger 
improvement then buying a super-premium diagonal to reduce light 
scatter.  It is less taxing on your wallet, too!

> --- Gil McFarlane <gilboastro@yahoo.com> wrote:
>>Any
>>thoughts versus antares or protostar for about $75? 

AstroSystems is another possible source.  The easiest route is to buy 
the secondary and holder and then make a wire spider.  Alternatively, 
buy only the secondary, glue the mirror to a home-made holder, and 
save another $35.

	Mike Lockwood

_______________________________________________
ATM mailing list http://www.atmlist.net/