The TAURUS Tunable Filter (TTF) affords a new approach to observational cosmology, allowing a wide field (10 arcmin) to be imaged monochromatically in contiguous wavelength intervals (6–60 Å bandpass) over the R and I bands. In a 200 s exposure with the AAT, the TTF can detect Hα emission powered by star formation rates as low as 0·1 M⊙ yr−1 at z = 0·08 and 1 M⊙ yr−1 at z = 0·24 in 2 arcsec seeing (cf. 0·26 M⊙ yr−1 for the LMC). In this paper we describe an emission-line survey currently under way using the TTF on the AAT to detect redshifted Hα over the ranges z = 0·06–0·1 and z = 0·22–0·26. Such detections will be of timely interest to the Southern HI Sky Survey which is motivated along similar lines.
