LX200GPS.CRCM.NET (Astronomy)

The Construct & modification of a Meade LX200GPS Telescope.

Meade LX200GPS Telescopes (OTA optical & mechanical Simulator)

These files were last updated 1300 GMT, 09 November 2007

The Simulator how does it work?

The simulator works by method of ray tracing.

On hundred equispaced, equienergy and parallel rays are projected at the input to the telescope. The rays are symmetrical and equispaced across the diameter of the telescope aperture and are entered on the mechanical axis of the optical tube assembly (OTA). For ever mechanical configuration change made to the OTA all rays, are re-calculated.

For each ray it is considered that there are; Reflecting, Refracting, transmitting and absorbing media within the telescope and at every interface a new vector for the passage of the ray is calculated.

At a refracting surface the change in vector of the ray is calculated using the refractive index of both media, the angle of incidence at the interface and the temperature of the materials.

At reflecting surfaces it is simpler and only the angle of incidence and angle of reflection needs to be calculated.

At an absorbing surface the ray is terminated.

For travel within a material (even air) the distance of travel is modified by the temperature of the material.

The positioning of ray modifying elements is controlled by a 3D CAD model of the OTA which recalculates the ray transit from interface to interface for mechanical input variations. Mechanical variations include, linear and angular movement of the positions of the ray modifying elements, to which temperature effects are applied.

When the passage of all the rays through the OTA has been calculated they are integrated across the image plane to produce the Energy section of the image. The intercepts of the rays on and off axis and the associated variation in Back Focus position produces the distinctive behaviour of the image produced by the Schmidt-Cassegrain Telescope.

By adjustment of the various user parameters is possible to replicate the effects of Mirror Flop, Collimating errors, Corrector plate miss alignment plus much more.

A Note:

The Corrector Plate (lens) is the most difficult element to model, and also the most difficult element to measure.

It was decided that it could only be implemented, if the lens shape was constructed in the simulator from the manufacturing process.

This process is to bend a flat glass plate, by applying a vacuum to one side to cause the plate to Dish with the shape of a Diaphragm. While dished, a spherical grinding of the plate takes place, such that when the vacuum is removed the Corrector plate relaxes to its original shape with the surface modified to produce an Annular Concave Lese.

Correctors can be produced with the process being applied to either one or both surfaces. The model will handle both scenarios.

In the case of the Meade 8" SCT Corrector, only the exit face is figured.

The input variables for the manufacture of the corrector lens are;

The Diameter of the finished Corrector Lens The Radius of the Zero Refraction annulus of the lens

The deflection introduced by the differential pressure during grinding

The number of surfaces that are figured

The finished thickness of the corrector lens at its overall diameter.

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