My LX200 and CCD camera are remotely controlled from an adjacent annexe - the 'scope can be seen through a glass observation panel. The self-contained SBIG spectrometer, at the telescope focal plane, has four external controls. Control of three of these have now been transferred to the annexe via 15ft of phono cabling [9v DC max] with switches placed next to the PC mouse. This proves very convenient and improves productivity. The modifications are of a very minor nature [and low cost] and don't compromise the integrity of the spectrometer. The purpose of each facility is briefly explained.
1] Slit illumination - the second CCD within the ST-7/8 serves a dual
role -
[a] to autoguide the telescope and 'hold' the star on the slit
during prolonged exposures and
[b] allow 'viewing', focusing and centring the star over the
slit in the first place - a vital facility.
In its absence the observer is effectively working 'blind' for the main imaging chip serves only to record a spectrum. The slit is back illuminated into a bright line via a tiny LED within the spectrometer triggered by an external switch and internal 9vDC battery. A second over-riding switch is placed next to the PC mouse - marked biLED.
2] Grating micrometer - each grating within the spectrometer can be tilted to centre any spectral region onto the CCD via a micrometer screw. A reading of 4.86 will bring the hydrogen-beta line [Hb @ 4861A] close to the centre of the downloaded images in hi-res mode. A lightweight electric focuser [Tasco #1603EF] bolted to the spectrometer base [via existing screw holes] has a reversible belt drive to the micrometer shaft. The black button on top of the motor declutches the drive for manual rotation of the micrometer shaft. Positioning of the spectrum is controlled via item 3 below.
3] Reference source - a small 8mm opal window [with cover] on the spectrometer base allows a source of light with bright emission lines to be added to a spectrum for precise calibration by wavelength needed for measurement of Doppler Shifts etc. I have used a miniature battery powered fluorescent lamp [£4 / $6 at DIY stores] as a source of mercury [Hg] light. The lamp [removed from its casing] is slid into an aluminium tube to screen extraneous light and clipped to the spectrometer base. A small hole admits Hg light to the reference window.
4] Grating selection lever - this rotates the grating carousel through 180 degrees to bring either the low-res 150 lines/mm grating or the hi-res 600 lines/mm grating into play. This continues to be operated from the spectrometer itself as it is unusual to continually swap from one grating to another during a session.
The calibration spectrum is from the mercury [Hg] lamp [see above] plus a neon [Ne] lamp [warning light in domestic appliances]. Both produce sharp emission lines of known wavelength - the values are estimated here except for Hg in the UV/visible. The Hg source covers the UV to green region whilst Ne has many lines in red. Both lamps appear to share common lines into the near IR - probably argon [Ar].
