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Although TAURUS--2 was originally constructed primarily for use as a Fabry--Perot interferometer, it can also be used as a focal reducer for imaging observations.
The advantage of using TAURUS for imaging observations over using a CCD direct (e.g. at the auxiliary port of the A&G) is that it provides a plate scale better matched to the image size. When an EEV CCD with a pixel size of 22 micron is used direct at f/11, the scale is 0.1 arcsec/pixel, oversampling the image and providing only a limited field. TAURUS with the f/4 camera provides a scale of 0.27 arcsec/pixel, whilst TAURUS with the f/2.1 camera provides a scale of 0.51 arcsec/pixel.
The disadvantage of using TAURUS over using a CCD direct is the extra optical elements. These have a throughput of about 60 per cent (see section 17), and increase the risk of ghosting (see section 19) and stray light.