RC 500 telescope

Table of contents :

500 mm f/3-8 Ritchey - Chretien telescope

OSLO model:

NB: By comparison, the M1-M2 distance of the Astrosib RC 500 f/3-8 is 994 mm (instead of 1009.1 mm) while the backfocus (from the surface of M1) is 335 mm (instead of 300 mm).

Sensitivity of Strelh ratio to backfocus:

The RC design is very sensitive to backfocus. In order to keep the Strelh ratio > 0.9, the backfocus should be within +/- 20 mm of its nominal value.

By comparison, the field covered by the ASI1600 (4536 pixels × 3520 pixels × 3.8 microns) at 0.08 arsec/pixel resolution is 0.1° × 0.08°

For the nominal M1-M2 spacing, the radius of the diffraction limited flat field of the RC 500 f/3-8 is 0.11° :

rms Optical Path Difference of a 0.11° radius:

500 mm f/3-8 Ritchey - Chretien telescope with the 2× triplet short Barlow

With the 2× triplet short Balow lens (f = -54.95 mm), the radius of the diffraction-limited flat field is 0.06° in green light :

500 mm f/3-8 Ritchey - Chretien telescope with the 2× Clavé Barlow

With the 2× Clavé Barlow lens (f=-113.4 mm), the radius of the diffraction limited flat field shrinks to 0.035° in green light:. Coma increases dramatically away from the optical axis:

500 mm f/3-8 Ritchey - Chretien telescope with 2× "Long Barlow"

With the 2× "Long Barlow" lens (f=-142.3 mm), the radius of the diffraction-limited flat field is 0.074° in green light:

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