Table of contents :

Introduction

Newtonian telescope

Dall Kirkham 200 mm F/4- F/15, Mewlon 210 F/2.9-F11.9 and Mewlon 250 F/3-F15

Gregory 250 mm F/3.2-F/28.4

Cassegrain 200 mm F/4-F/15 and Cassegrain 350 F4.9-F29.2

Celestron "classic" and Edge-HD versions overview

Celestron 8 classic and Edge-HD

Celestron 14

Celestron 14 with optimized Schmidt plate position

Celestron 8 with optimized Schmidt plate position

Celestron 14 classic and Edge HD

CDK 355 mm F3 - F11.8

Barlow lenses

 


 

Celestron 14 "Classic" design with optimized Schmidt plate position

 

OLSO model :

- The model for the "classic" C14 is from Ken Hutchisson and Thierry Berthe, and is a "best guess" given actual measurements and data available.

Optimized design :

- In a Schmidt telescope, the distance between the plate and the mirror is equal to the radius of curvature of the mirror. The distance between the focus and the mirror is equal to half the radius of curvature of the mirror.

- The field correction of a Schmidt-Cassegrain telescope can be improved by increasing the distance between the Schmidt plate and the primary mirror. All other optical characteristics are left unchanged.

Nominal design of the C14 "classic":

 

Variant with the Schmidt plate positioned 400 mm ahead from nominal position :

This variant appears to be the optimal one in terms of diffraction limited field.

 

Radius of the diffraction limited flat field :

The radius of the diffraction limited flat field increases by a factor of two when the Schmidt plate is positionned 200 mm from nominal position, and by a factor of four when it is positionned 400 mm ahead from nominal position.

As a comparison point, and according to the Celestron WhitePaper, the radius of diffraction limited flat field of the C14 Edge-HD is 12.4 arcmin in green light.

 

Spot diagram of the "classic" C14 design over a 0.12° field (flat field):

Spot diagram of with the Schmidt plate positionned 400 mm ahead of nominal position :

 

Comparison of the spot diagram over a 0.25° field (flat field)::

 

 

Strehl ratio versus wavelength (on the optical axis):

Same as for the "classic" C14 design.

Focus versus wavelength (obsolete figure ...to be updated):

Same as for the "classic" C14 design.

 


 

 

 

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