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Some comments

The effective wavelength and bandpass of a filter can be strongly modified by the detector response. This is most serious at the extreme blue and red limits of detector sensitivity and would be much less noticeable with narrow band filters.

Thinned (blue-sensitive) CCD's suffer from internal interference effects which give fringe patterns when exposed to "monochromatic" light. In practice narrow band filters will invariably give fringes (Å) and broad band filters usually give fringes from narrow night-sky lines, and any narrow band emission from a source would give similar results.

There are at present no continuum filters to give measurements in-between the emission-line filter set.