Re: Oil-spaced quadruplet - anybody made one??

From: brian (brianc1959_at_aol.com)
Date: 06/10/04 

Date: 10 Jun 2004 12:49:11 -0700

atasselli@hotmail.com (andrea tasselli) wrote in message >
> Never tried my hands at designing one but I do suspect that you won't
> have diffraction limited performance in the i-t band even with CaF2,
> if all surfaces are to remain spherical. As for the practical pitfalls
> these glasses are a pain in the neck to work with and I had just
> enough trouble with a run-of-the-mill 3-element objective.
>
> Andrea T.

Hi Andrea:
I'd be curious to hear about your troubles with a "run-of-the-mill" 3
element objective.

Below is one of my better i-t (365nm - 1014nm) quadruplet designs.
Strehl is greater than 0.8 over the whole waveband, and greater than
0.95 from about 430nm to 950nm. Spherochromatism is well controlled,
although there is a trace of spherical aberration which could be
removed by figuring. If you do this then its possible to get better
than 0.99 Strehl over most of the visible waveband. Whether this has
any practical implications or no remains to be seen. I feel pretty
safe in calling this design a true superachromat, with four color
crossings at all zones, minimal spherochromatism, and no coma.

Note that I'm using a custom modelled version of fluorite based on the
Schott Lithotec data***. If you use the standard ZEMAX (and
probably OSLO) fluorite then the correction will be damaged enough to
require re-optimization.

I'd prefer a triplet, obviously, but just haven't been able to design
one that I like well enough. As Roland Christen once said, APO
triplets are easy to design. However, really good APO triplets are
considerably harder to design.

I've found that two quadruplets using the glasses below plus a field
flattener will make an amazingly good Petzval lens. If only I could
afford 14" diameter CaF2 blanks! Perhaps when 157nm lithography
becomes obsolete there will be some good bargains available in large
chunks of UV-grade fluorite . . .

SURFACE DATA SUMMARY:
Surf Radius Thickness Glass Diameter
 OBJ Infinity Infinity 0
 STO 315.2717 12 S-LAM3 150
   2 211.1908 22 CAF2SCHT 150
   3 -1010.737 15 S-LAH60 150
   4 -229.4219 10 S-LAH53 150
   5 -2933.665 1008.949 150
 IMA -500 9.187263

INDEX OF REFRACTION DATA:
Surf Glass 0.404000 0.435000 0.486000
   0 1.00000000 1.00000000 1.00000000
   1 S-LAM3 1.74312941 1.73604181 1.72750655
   2 CAF2SCHT 1.44153411 1.43951393 1.43701528
   3 S-LAH60 1.87423505 1.86304259 1.84984709
   4 S-LAH53 1.84101310 1.83139996 1.81996876
   5 1.00000000 1.00000000 1.00000000
   6 1.00000000 1.00000000 1.00000000

Surf Glass 0.546000 0.589000 0.656000
   0 1.00000000 1.00000000 1.00000000
   1 S-LAM3 1.72056958 1.71689398 1.71254318
   2 CAF2SCHT 1.43493130 1.43380722 1.43245773
   3 S-LAH60 1.83933319 1.83383636 1.82739791
   4 S-LAH53 1.81078423 1.80595377 1.80026742
   5 1.00000000 1.00000000 1.00000000
   6 1.00000000 1.00000000 1.00000000

Surf Glass 0.707000 1.014000 0.365000
   0 1.00000000 1.00000000 1.00000000
   1 S-LAM3 1.70999876 1.70111411 1.75531400
   2 CAF2SCHT 1.43165815 1.42878834 1.44489006
   3 S-LAH60 1.82366957 1.81093871 1.89403987
   4 S-LAH53 1.79695796 1.78550709 1.85783223
   5 1.00000000 1.00000000 1.00000000
   6 1.00000000 1.00000000 1.00000000

ELEMENT VOLUME DATA:
Values are only accurate for plane and spherical surfaces.
Element volumes are computed by assuming edges are squared up
to the larger of the front and back radial aperture.
Single elements that are duplicated in the Lens Data Editor
for ray tracing purposes may be listed more than once yielding
incorrect total mass estimates.

                             Volume cc Density g/cc Mass g
Element surf 1 to 2 252.742060 4.250000 1074.153755
Element surf 2 to 3 243.896269 3.181000 775.834031
Element surf 3 to 4 179.352117 4.430000 794.529880
Element surf 4 to 5 278.571739 4.430000 1234.072806
Total Mass: 3878.590472

Brian
www.caldwellphotographic.com