From: "Richard F.L.R. Snashall" 
To: atmlist 
Reply-To: "Richard F.L.R. Snashall" 




Bob May wrote:
> Not explictly only TOT but some guys have ended up with a fair bit of their
> work that way after going too far with the initial grinding.
> I've got to do a thin mirror one of these days so that I can see what the
> problems are.  Righ now, I've got a 6" refractor that I'm going to build as
> a finder scope for my 200" refractor.  The glass is from Jan Sugaski's
> little sale of 6" and 4" refractor glass and I'm going to do
a F8 with the
> following curves:
> R1 = 29.64":
> T1 = .590"
> R2 = 19.21"
> T2 = .040:
> R3 = 19.22"
> T3 = .512:
> R4 = 61.34"
> RoweTrace tends to indicate that this is a good set of numbers for the BSC2
> and SF12 glasses.  Anybody got better numbers for this?  I'll note that the
> results tend to indicate to me that there may be a need to parabolize a
> surface to reduce spherical aberration.

If the last three radii are negative, I get lambda/20 RMS at 509.4 nm and
lambda/90 RMS at 597.4 nm (using BK7 in lieu of BSC2, though). How much
parabolization would you want?

        Rick S.

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