Lone Star Observatory Optical System Specifications
(All specifications confirmed by laser interferometery)
Classic Cassegrain Mirrors Configured by Jerry Brunache, Carlsbad, Ca
| Primary Mirror | |
| Diameter | 24 in/0.61 m |
| Type of glass | Pyrex |
| Original glass blank thickness | 4.25 |
| Final thickness of shaved blank | 4.00 in |
| F/ratio of primary | 5.30 |
| Focal length of primary | 127.22in/3,231mm |
| Diameter of center core hole | 7in |
| Weight of cored primary mirror | 131.19lbs |
| Coating | HiVac Enhanced Aluminum w/dielectric overcoat |
| Coating applicator | QSP Optical |
| Percent light reflectivity | 96% |
| Beveled edges | Less than 0.125 in |
| Secondary Mirror | |
| Diameter | 8.25in |
| Type of glass | Pyrex |
| Thickness | 1.375 in |
| Secondary magnification | 2.997 |
| Secondary radius of curvature | 115.125 in |
| Conic constant on secondary | -3.978 |
| Image size on secondary | 8.05in |
| Weight of secondary | 5.51lbs |
| Coating | HiVac Enhanced Aluminum w/dielectric overcoat |
| Percent of light reflectivity | 96% |
| Overall Optical System | |
| Cassegrain f/ratio | 15.889 |
| Focal length | 381.33 in/9,686 mm |
| Back focus distance | 25.81 in (primary vertex to image) |
| Primary/Secondary separation | 88.938 in |
| Radius center of curvature | 254.125 in |
| Magnification loss | 0.10 |
| Light loss | 10% |
| Diffraction effect | 32%R |
| Image size | 3.40in |
| Light gathering ability | 8,019 times human eye |
| Theoretical resolution capability | 0.190 seconds of arc |
| Theoretical max power @ 50 times aperture | 1,200X |
| Useable max power @ 30 times aperture | 720X |
| Minimum useable magnification @ 3.5 times aperture | 84X |
| Theoretical magnitude of faintest star visible | Mag 16.9 |
| Widest field of view (lowest power wide field eyepiece) | 18 min of arc |
| Optical System With 2X Telecompressor Installed | |
| System f/ratio w/Telecompressor installed | 7.945 |
| Focal length w/Telecompressor installed | 190.67/4,843mm |
| Diameter of Telecompressor | 3.165 in |
| Length of assembled Telecompressor | 4in |
| Number of lens elements in Telecompressor | 4 |
| Image size with Telecompressor installed | 1.75in |
| Back focus with Telecompressor installed | 19.66 in |
| Widest field of view (lowest power, wide field eyepiece | 36 min of arc |
| Wave Front Accuracy |
|
“The axial wavefront error of the system was measured
over several 20-inch diameter sub-apertures. The system tests were
performed at a wavelength of 6328 Angstroms using a 1/20th
wave 20-inch clear aperture optical flat and a scatter plate
interferometer. The worst of these measured slightly better than 0.070
lambda peak-to-valley, yielding a total system wavefront error of
lambda/10.2 peak-to-valley (slightly better than 1/10th wave).
The system is actually better than the peak-to-valley wavefront numbers
indicate. Using the Root Mean Square (RMS) wavefront error as a measure of
quality, 0.070 lambda is usually considered diffraction limited. The
system actually measured 0.023 lambda, three times better. Mounted and
aligned properly, the system performance will be limited by atmospheric
conditions under virtually all circumstances.”
Don Small, Senior Optical Engineer, Perkin-Elmer |