Interferograms for Four High Quality Telescopes
and Two Commercial Telescopes

by Roland Christen

Here you can compare 4 high quality scopes of different types with two
commercial scopes. It must be noted that all scopes meet or exceed their
manufacturer's specifications. Compare the roughness of the wavefront of the
different types of scopes. The effect of roughness is to scatter light from the
Airy disc into the diffraction rings. In the case of planetary viewing, it
creates a thin veil of light that lowers contrast. To give you an idea of the
sensitivity of these interferometer tests, even the worst scope (8" SCT) shows
very close to straight lines when a Ronchi grating is placed at the focal
point.

The interferometer is an order of magnitude more powerful in showing wavefront
defects. It can show whether an optic has been made accurately as well as
smoothly. If it is smooth, the Strehl ratio will be high, even if the P-V is
somewhat lower. When examining or comparing interferograms or test reports, one
would need the actual fringe image, not just the wavefront or surface plot.
Without the fringe picture, I would not draw any conclusions, and the test
report is pretty much useless and incomplete in my opinion.

Interferograms


High quality premium make Newtonian mirror.

High quality RC optical set.

High quality competitor apo lens.

A production 130 EDF lens.

Commercial 7 inch Maksutov Cassegrain.

Commercial 8 inch Schmidt Cassegrain.



 
Roland Christen, ASTRO-PHYSICS

Return to Roland Christen Images and Essays.