[ATM] re Ross Null Test-would this lens work?

[DrewClan@aol.com]

Hey, Gil! I've done a couple of mirrors with similar Surplus Shed and  
Edmunds pcx lenses and think that for personal use on amateur telescopes  they work 
fine. There is nothing like a null test! If you look back in  the old TM 
magazine (issue number 49 I think but don't quote me), you'll see a  well known 
professional saying the same thing about cheaper lenses in the  letters to the 
editor. I don't think a pro would be able to sell mirrors  done this way, but us 
amateurs don't necessarily have to spend an arm and a leg  on a pcx lens. So 
go for it! Remember to change the index of refraction in the  ross null xp 
program, and also to figure the RoC of the lens (xp doesn't  use the focal 
length). Be sure to look at the mirror both at focus  with the pcx lens and at the 
radius the good old fashioned way to check your  work. Back up your null 
testing with some zonal foucault readings to play it  safe. I would be very 
interested in hearing how things go for you as I  think this is an underutilized test 
for atms. Jay
 
<<<I would like to try the Ross null test - but spending
$500  for a lens is out of my budget.>>>