[ATM] Sizing you secondary mirror

[Corona Australis]

Thanks Mel and Ken that's exactly what I was looking for.

Cheers,CS

Rob

-----Original Message-----
From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Mel Bartels
Sent: Wednesday, 1 September 2010 10:42
To: atm at atmlist.net
Subject: Re: [ATM] Sizing you secondary mirror

Here's an online tool http://www.bbastrodesigns.com/diagonal.htm

Looks like a 55mm diagonal will be just fine:

Mirror diameter 254mm
Focal length 1200mm
Diagonal size 55mm
Diagonal to focal plane 160mm

Off-Axis	Illum.	Light Loss
0.00 mm	100.0%	  0.00 mag
2.00 mm	100.0%	  0.00 mag
4.00 mm	100.0%	  0.00 mag
6.00 mm	100.0%	  0.00 mag
8.00 mm	100.0%	  0.00 mag
10.0 mm	100.0%	  0.00 mag
12.0 mm	100.0%	  0.00 mag
14.0 mm	97.45%	  0.02 mag
16.0 mm	92.72%	  0.08 mag

Mel Bartels


-----Original Message-----
From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of
Corona Australis
Sent: Tuesday, August 31, 2010 4:23 PM
To: atm at atmlist.net
Subject: [ATM] Sizing you secondary mirror

Hi folks,

What is the formula for working out the optimum size of your secondary
mirror?
I'm looking for full illumination. I used to have it somewhere but can find
it, any
help greatly appreciated. The mirror being used is as follows

Diameter 254mm 
Focal Length 1200mm 
F/ratio F/4.7

Btw, this doesn't need to be turned into a great debate on the pro and cons.
The 
formula would do nicely.

Cheers,CS

Rob




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