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Secondary Mirror Selection - WWYD?

Started by eyork, 07/09/2004 11:49AM
Posted 07/09/2004 11:49AM Opening Post
Simple question, what would you do?

I used NEWT to determine the best size for my secondary. It says 2.05" Looking at premium secondaries, my options seem to be 1.83" and 2.14".

Performance characteristics:

1.83" - 5% Primary surface area obstruction, .3558 in (9 mm) 100% illumintaed, 1.168 in (29.7 mm) 75% illuminated. $120

2.14" - 7% Primary surface area obstruction, .7398 in (18.79 mm) 100% illumintaed, 1.517 in (38.5 mm) 75% illuminated. $180

Posted 07/09/2004 01:30PM | Edited 07/09/2004 01:31PM #1
I would go with the larger mirror. The biggest reason would be that you would be using the inner sweet spot of the mirror and not the edges where most error is found. By doing this you can get virtually a better mirror. If you use the whole mirror, using a smaller one, then the turned edge will be used too. Almost every flat is going to have some sort of turned edge, even a 1/20 wave mirror. Most P/V ratings are because of this turned edge, it can take a 1/20 wave overall and make it a 1/4 wave in extreme circumstances.
Pyrex mirrors new from Antares Optics. These are better prices than you were stating. Add 20% for Fused Silica (Quartz) Enhanced Aluminum 96-98% reflectivity too!

2.14 1/12 $79.99

2.14 1/14 $99.99

2.14 1/15 $109.99

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