Spectroscopy - Frank Johns

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Astro Equipment
SPECTRA L200 Spectrograph - This Littrow type spectrograph was built from a kit conceived and supplied by Ken Harrison, since heavily modified. The variable slit was replaced by a system of alternate slits. Initially 30 micron is used. Other mods include:
    a. Motor operation of the grating micrometer
    b. Webcam to view the micrometer settings
    c. Servo to operate the Neon Calibrating lamp
    d. Replaced original 600 l/mm grating with one of 1800 l/mm
These items are remote controlled via the PC
A Vixen Flip Mirror was modified with a 95%/5% beamsplitter to guide on the target star. However the thin glass plate gave a double image, which was OK but at 5% it ruled out the feinter stars for guiding. A beamsplitter cube giving a 50/50 split was tried but this was replaced by a pellicle.
Helical non-rotating focusers for both the guide and imaging cameras were made by modifying standard camera lenses.

The Star Analyser 100 - by Paton Hawksley - is a high efficiency 100 lines/mm transmission diffraction grating, blazed in the first order.
The grating is mounted in a standard 1.25inch filter module. This allows it to be screwed into a camera nosepiece or even into an eyepiece. 
By mounting the Star Analyser at the appropriate distance from the camera chip, it is possible to image the star (zero image) and the first order spectrum.

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