cassegrain telescope 12.5 in f12.5

cassegrain telescope on cloudynights, which is also on S&T Oct 2006

from mike lockwood:

given:

R2(sec ROC) = 47.35"

secondary distance to primary focal point p (circled in orange) = 15.72"

conic of primary = -1 (parabola)

conic of secondary = -4 (hyperbola)

appendix on CassDesign:

Unvignetted Field Width at Cass focus is the dimension in the user-chosen units.

P = distance of secondary vertex inside primary focus
P' = distance from secondary vertex to final Cass focus

The back working distance (BWD) is from the primary mirror vertex to Cass focus. It is also P' - SEP, where SEP is the vertex-to-vertex mirror separation.

BWD must be personally chosen to include enough distance for the primary mirror thickness, the primary support system, the back plate thickness, the optical path length through any fold optics, the height of the focuser, and the desired distance from the top of the focuser (maybe at midpoint travel setting) to the focal plane.

BWD is entirely up to how the user wants to make his/her Cass and what hardware is to be used.

cassegrain data:

AMP: secondary to system focal plane / secondary to primary place, ie "Magnification" of system

EFL: effective focal length

software download here

Online app . NB the conic constants are default negative values ( enter "1" for conic of -1)

BFL is back ( exit) distance from primary to system focal plane

Chris Forder build similar design into a DK

Design tools repo from France astronomy SAF

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