STARTEST IMAGES GALLERY
Cassegrain250_1

Type: Schmidt Cassegrain
Aperture: 254 mm
Focal length: 2500mm (f/10)
Secondary obstruction: 94mm (37%)

Images copyright
Markus Ludes (c) 2001
Picture

Inside Focus

Inside Focus

Outside Focus

Outside Focus

“These images shows a typical 10" Schmidt cassegrain quality, not the best, but also not the worst.  It has some minor spherical errors and around the central hole you see on one side two dimmer rings and on the other side these two inner rings that are a bit brighter, which comes from a zonal error. In general this is a telescope with acceptable good optics”

Markus Ludes (APM-Telescopes)
Note: ronchi-testing with 254 lines/inch or 100 lines/cm.
Picture
Picture

This simulation was run on the green channel of the second original image from the left (inside focus). Although only three rings are visible the amount of defocus in this obstructed telescope is allready large (>15 waves). That’s why I did not attempt to simulate the leftmost image. The overal fit of the - 0.12 wave LSA and +0.15 HSA was easily found and therefore the simulation is probably reasonably good. The total wavefront is estimated at 0.21 (1/5) PTV and 0.046 (1/22) RMS. The zonal error that Markus mentioned is not visible in the above original.

Cor Berrevoets