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Luke,
if you put the lamp at the focal position of a finderscope or camera lens, the light exiting the lens will be parallel (like starlight) If you then point the finderscope with the neon bulb at your main telescope and align them correctly, the main telescope will concentrate the light from your artificial neon star on to the spectrograph's slit. You could conceivably focus sufficient light on to the slit from the neon as to warrant attenuation.
best
c
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