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Optical design & Instrumentation

Ivan Syniavskiy

CAMESPIR - IrfraRed (1-2.5 micron) CAMERA SPectrometer for the WHT telescope

CAMESPIR is an optical instrument designed to observe between 1000 nm and 2500 nm.
Imaging shall be possible with both, broad band filters J H K' and narrow J-continuum Pa-beta H-continuum K-continuum band filters, over a Field of View of 6 3arcmin on the sky. This instrument is seeing limited (0.7 arcsecond median seeing as design parameter).

Optical Design

Collimator

The collimator design is based on the determination of the exit pupil of the optical system. The exit pupil of optical system is an image of aperture diaphragm (the primary mirror telescope) followed by optical elements (lenses). Using this approach we can get the pupil of the telescope with minimal aberration.

To calculate of a collimator: 1- the main telescope mirror; 2- the secondary mirror; 3- the collimator
The collimator: 1- the telescope focal plane, 2,4 - achromatic doublets; 3- the lens; 5-the pupil

Camera

The camera consists of six lenses, two of which interaction are doublet for correcting chromatic aberration [4, 5]. All lenses are transparent in spectral range from 1000 to2500 nm. There are no cemented surfaces.

Camera Detail: The design consists of 6 lenses. The distance between the last lens and the detector is 89 mm

Complete CAMESPIR optical design

Multi Configuration mode was used a in Zemax: Configuration 1 – Full system; Configuration 2 – to keep parallel light direction near of the telescope pupil place; Configuration 3 – for image of the telescope pupil.

The layout for CAMESPIR optical design: 1- the focal plane, 2 - the cryostat window; 3 – the doublet of a collimator, 4- the fold mirror, 5- the lens of collimator, 6- the fold mirror, 7- the lens of collimator, 8 – the filter ( placed in pupil), 9- the camera
The spot diagram: 1- at a center FOV; 2- at a half FOV;3- at a corner FOV
The geometric Encircled Energy at the centre FOV ( 0 deg), at a near half FOV -(0.03 deg), at a corner FOV (0.07 deg)
The field Curvature and Distortion

Mechanical Design

Camera Lens with focusing mechanism

The chamber is designed as a separate unit (barrel). Calculations showed that the refocusing optics (replacement filters) must be made within + - 0,15 mm. This movement can be done piezo actuators *. The high demands on the positioning of the first and second lenses cameras are present. As an option should provide additional screws to decenter them in a barrel. But the landing should not be rigid, so the lens does not so the lens did not break during cooled.

* - http://www.noliac.com/Plate_benders-57.aspx

The camera lens: 1- threaded ring; 2- lens barrel; 3- piezo focusing mechanism

Complete CAMESPIR mechanical design

The complete CAMESPIR mechanical design is presented in the next fig.

The mechanical design of the CAMESPIR instrument (without fringe tanker): 1 - the plate; 2 - the doublet collimator; 3 - the fold mirror; 4 - the lens collimator; 5 - the fold mirror; 6 - the doublet collimator; 7 - the filter wheel; 8 - the camera; 9 - the shutter; 10 - the IR detector