re:ATM commercial optics

[Howard.Banich@nike.com]

There's a number of places to get a quality 6" f/8 commercial mirror. I've 
seen good mirrors from Orion, Edmunds, Parks, Swayze, and I'll bet just about 
every company that advertises them. Not to come across too naive, but this 
size and focal ratio should be pretty darn good no matter where it comes from. 
Even so, star test it as soon after getting it as possible (Dick Suiter's 
book "Star Testing Astronomical Telescopes" is real helpful for this). A note 
of realism - it's always possible to get a lemon no matter how reputable the 
firm. Oops happens... 

The exact focal length should either be inscribed on the mirror or come with 
its documentation. If not, you can check it directly by carefully measuring 
how far away from the mirror's front surface it forms an image of the sun. 

Diagonal size is something of a personal preference, but smaller is usually 
better - to a point. My humble opinion is that you'll do fine with a 1.3".

Have fun, I'll bet you'll enjoy your scope for a long time to come.

----------------------[Reply - Original Message]----------------------

Sent by:Matt Devine <mdevine@nuera.com>
 Hi guys, I'm in the process of building a six inch f/8 Dob.  I have run the
numbers in Berry's book many times and am confident that I am on the right
track with the hardware I plan to buy.  I do not plan to grind my own mirror
this time, that will be the next scope.  Does anyone have a good source for a
six inch mirror.  I had assumed that you could not go wrong using some of the
"larger" telescope manufacturing companies, but I'm not so sure now having 
read
some of the past mail.  Any happy customers or info would be appreciated.  
Also
I plan on using a low profile focuser (JMI), and a 1.30" secondary.  According
to the math, the exact secondary size would need to be 1.21".  Can I reduce
this size, or would it be advantageous?  I plan to use this scope for visual
only.  The last question I have is on focal length.  If a commercial 6" mirror
(f/8) can vary +/- 3%, how do you know what the exact focal length is?  Are
they stamped with this info?  Thanks in advance.

Matt Devine
San Diego, Ca.

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