The IIIaF emulsion and a RG630 filter results in a useful spectral range from 6400 to 6850 Å (dispersion of 1950 Å/mm at Hα), i.e. Hα line in emission can be record for objects up to z<0.04.
Field coverage is 5.5x5.5 square degrees in plates 24 cm wide (plate scale is 86 arcsec/mm).
The IIIaF plates were hypersensitized by baking them in an atmosphere of N2 gas at 65 C for 6 hours prior to exposure.
Without widening, the spectra were kept to a width of 0.06 mm. Dispersion runs along the north-south axis. A well-exposed spectrum is about 0.4 mm long.
- good seeing (no worse than 3 arcsec) and excellent guiding,
- no cloud interference
- no exposure interruption
- telescope near the meridian, i.e. hour angle between 21h30m and 2h30m.