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Star/RCOS Lawsuit The Facts
 
Lawsuit Settled 01/23/08

RITCHEY-CHRETIEN OPTICS
PROFESSIONAL SERIES

Specifications for standard design optics follow.

PART NUMBER

RITCHEY-
CHRETIEN
PRIMARY
FOCAL LENGTH
BACK
FOCUS
SPACING
SECONDARY
PRIMARY
HOLE
RC-12P
12.5" f 9
40"
12"
26.5"
4.80"
3.5"
RC-14P
14.25” f 8
40”
13”
26.4”
5.50”
3.50”
RC-16P
16" f 8.4
48"
14"
31.7"
6.00"
4"
RC-20P
20" f 8.1
60"
15"
39.7"
7.60"
4.5"
RC-24P
24" f 8
72"
16"
48.2"
9.00"
5.5"
NOTE: Additional sizes and focal lengths can be manufactured on a custom basis.
Please contact us for information.

WHY IS STAR INSTRUMENTS' RITCHEY-CHRETIEN DESIGN
SUPERIOR TO PRODUCTION-TYPE SCHMIDT-CASSEGRAIN SYSTEMS?

Below are spot diagrams for a 12.5" f9 Ritchey-Chretien versus an 11" f10
Schmidt-Cassegrain with an f2 primary and 5x secondary.This spot diagram would be comparable to all production Schmidt-Cassegrains. (1/2 degree off axis)

As you can see, the Ritchey-Chretien is several times better than the Schmidt-Cassegrain.
There are several reasons for this:

The lower the amplification factor of the secondary mirror, the flatter the field.
The Ritchey-Chretien system has a 2.7x secondary, whereas the Schmidt-Cassegrain has a 5x
secondary.
• Ritchey-Chretien is coma-free, whereas Schmidt-Cassegrain is not. Production-type Schmidt
Cassegrains use a spherical primary and secondary which do not correct for coma.
Ritchey-Chretien has a hyperbolic primary and a hyperbolic secondary which correct coma.
• Ritchey-Chretien only has two surfaces; Schmidt-Cassegrain has four. Therefore,
Ritchey-Chretien has less light loss.



OPTICAL FABRICATION

STAR INSTRUMENTS optics are of the highest quality and figured in our own facility by experienced opticians using modern equipment. Computerized polishing machines have been developed to improve optical quality of larger telescope mirror systems. Professional series optics are fabricated from Russian AstroSitall, which is a zero expansion glass, or upon request, Schott Zerodur, Corning ULE or Fused Silica. Pyrex is not a zero or low expansion glass and the homogeneous properties of the glass are not consistent enough to allow us to make high quality optics. Primary mirrors are fabricated using lightweight dish-type blanks or full thickness on request. Completed optical systems are supplied without coatings.

OPTICAL TESTING

STAR INSTRUMENTS uses optical flats up to 41" in diameter to test in autocollimation all optics to insure excellent performance. A Zygo interferometer and software is used to provide hardcopy interferometric test data that is supplied with each set of completed optics. Back focus and spacing information is etched on the primary mirror, and the Star Instruments Job Number is etched on both the primary and secondary mirrors.

OPTICAL QUALITY

STAR INSTRUMENTS guarantees a minimum of 1/4 wave front, 1/20 wave r.m.s. on all systems.
STAR INSTRUMENTS continues to be concerned with the false advertising claims being made by amateur optical suppliers who claim 1/10 to 1/20 wave optics. These claims tend to confuse the amateur astronomer into believing you must have 1/10 wave optics, when in reality there are very few 1/4 wave 8" and larger optical systems. The fact is that Pyrex is not a zero expansion glass and, therefore, cannot keep a figure better than 1/4 wave front.