Case study III - how deep for z?
20 m telescope, 2 arcmin FOV
120 objects/shot even with this small FOV
7 night exposure:
- Why not?
Traditional: 2-8 hour exposures for spectroscopy
- But this is DIFFERENTIAL method where all instrumental effects cancel out
- Continuum S/N = 5 on I=26 (B=28-29) objects
- ?Redshifts of extreme HDF objects