alliracomparison.html

Anssen Technologies.
Designers and Manufacturers of Astronomical Instrumentation.

Allira Series™ of Equatorial Fork Mounted Telescopes.

The Allira Series™ Optical Design and Comparison to Ritchey-Chretien Designed Systems.

Ray Trace Diagrams Comparison.

Included below are comparison layout diagrams of the Anssen Technologies Allira Series design and an equivalent Ritchey-Chretien system for comparison. In this example each system is working at f/8.0 and the comparison of their performance is considered over a 1.0 degree flat field maximum. Please note that in reality this is well beyond the effective useable field of the RC system, but still well within the useable field of the Allira Series optical system.

Ray trace schematic of Allira Series™ optical system at f8.0.

Ray trace schematic of typical R-C optical system at f8.0.

Off Axis Spot Diagrams Comparison.

These spot diagrams compare the transverse aberration of the Anssen Technologies Allira Series&153 (top) and Ritchey-Chretien systems over a 1.0 degree flat field. Clearly the Allira system is superior, with near diffraction limited performance over the entire field and spectral range.

For a 14" telescope an Airy disk in Sodium yellow light has an angular diameter of ~0.85 arc seconds (represented by the black circles in the spot diagrams above represent these Airy discs), and so in general the system will be limited by local seeing conditions rather than diffraction, but at the same time will be able to take full advantage of those rare nights of exceptionally good seeing.

Spot diagram of Allira Series™ Optical system at f8.0.

Spot diagram of typical R-C optical system at f8.0.

Field Curvature Comparison.

These field curvature graphs give some insight into the ray distributions in the preceding spot diagrams. Again the plot representing the Anssen Allira system is uppermost, the R-C below. In these plots the curves labelled "T" and "S" represent the tangential and sagittal astigmatic focal surface positions as a function of field angle. The vertical axis represents the best "mean" focal plane. In the case of the Anssen Allira Series&153 system there is relatively little astigmatism (little separation between T and S surfaces) and the Petzval curvature is near to zero. The R-C system has pronounced astigmatism, and it can be seen the large elongated spots in the outer field of the lower part of figure 2 are due to out of focus sagittal focal lines.

Field curvature of Allira Series™ optical system at f8.0.

Field curvature of typical R-C optical system at f8.0.

Transverse Aberration Comparison.

These transverse aberration graphs for the Anssen Allira and R-C systems (top and bottom respectively as previously) for which the optics have been both tilted and decentred with respect to the optical axis. In the case of the Allira system both the secondary mirror and corrector lenses have been decentred by 0.5mm and tilted by 1 minute of arc. For the R-R system the secondary mirror has been tilted and decentred by the same amount. Clearly, despite the fact that it is optically more complex than the R-C system, the Allira is not any more sensitive to misalignment than the R-C, an is in fact slightly less sensitive.

Transverse aberration diagram for Allira Series™ optical system at f8.0.

Transverse aberration diagram for typical R-C optical system at f8.0.