From: "CSC" 
To: "Atm" 
Reply-To: "CSC" 


        I like the recent OSLO triplet designs provided by Rick.  The pure apo
ray
trace results are exceptional. The files did not have the airy disk
included in the spot diagrams, which I think is a good gauge for optical
performance. Do you guys use it? It's easy to switch on using
Update/Operating Conditions/Spot Diagram/Show Spot.

        The matching radii are a nice feature, and would make it easier to make
these lenses.  I notice the f/ ratio went longer to control abberation, and
the spot eventually fell inside the airy disk.

        In Mackintosh's ATMT, Dick Buchroeder discusses what is possible for a
DOUBLET and finishes with some semi-apo designs. He states Kzfs1 as being
very unstable, and suggests Kzfsn4. The indices of these glasses are close
to each other so it is more difficult to control sphero, and necessitates
some deep curves. I chose ssk2 for the crown and found some nice designs
that reduced spherochromatism at the expense of pure apochromatism.

        The cost of these Kzf glasses is not too bad, and a doublet as
mentioned
above, would cost on the order of 5x a fraunhofer.  Ohara makes a OBPM51
that is similar to the Kzfs1, but no doubt has the same limitations of the
phosphate glasses.  Kzfsn4 and Ssk2 are stock glasses.

        Would coating help the durability of the Kzf glasses?  Ed Ting at NHAS
gave
a demo of a Takahashi Fluorite and said that coating protects the Fluorite
rear element. Is it assumed that all the modern coated Fluorites do not
suffer from degradation?

        Iowa Scientific offered TCT scopes, TCT optics, and these Kzf glass
doublets.  Any info re: his whereabouts?

        Below I include the basic design for a 5" f/15 which is nicely
diffraction
limited, and as close to apo as one would need. Far better than a Standard
doublet. The cost should be low and the deep curves may not be too bad.

        This was rendered in notepad, and I hope it translates back into a
*.len
file.


// OSLO 5.40 44680 40470 51615
LEN NEW "No name" 1960.6 5
EBR  63.0
ANG  0.5
DES  "OSLO"
UNI  1.0
// SRF 0
AIR
TH   1.0e+20
AP  8.7268677908e+17
NXT  // SRF 1
GLA SSK2
RD   888.9999999999999
TH   15.0
AP  63.0
NXT  // SRF 2
AIR
RD   -250.68
TH   3.0
AP  63.0
NXT  // SRF 3
GLA KZFSN4
RD   -245.2
TH   8.0
AP  63.0
NXT  // SRF 4
AIR
RD   3090.0
TH   1524.0
AP  63.0
CC   -0.5
NXT  // SRF 5
AIR
TH   398.3483972101591
CBK  1
WV 0.58756 0.48613 0.65627
WW 1.0 1.0 1.0
END  5
SDSA On
OPDF 1.0e-08
OPOC "*opabrs"
VAR NEW
V 1 5 0 TH 0.0 0.0 1.0 0.0063
V 2 4 0 TH 0.1 10000.0 1.0 0.0063
V 3 2 0 TH 0.1 10000.0 1.0 0.0063
END
OPE NEW
O 1 "OCM5" 1.0 "cma3"
END



Colin

--- BBBS/NT v4.00 MP