We present spectra of three gravitational lens systems taken with the Low Resolution Imaging Spectrograph on the W. M. Keck Telescopes .
All of the systems were discovered in the JVAS and CLASS radio surveys , which were designed to find lenses suitable for measuring H _ { 0 } .
Previous spectra of these systems had low signal-to-noise ratios , and only one of the source redshifts was secure .
Our observations give unambiguous lens and source redshifts for all of the systems , with ( z _ { \ell } , z _ { s } ) = ( 0.4060,1.339 ) , ( 0.5990,1.535 ) and ( 0.4144,1.589 ) for B0712+472 , B1030+074 and B1600+434 , respectively .
The observed image splittings in the systems imply that the masses of the lensing galaxies within their Einstein rings are 5.4 \times 10 ^ { 10 } , 1.2 \times 10 ^ { 11 } , and 6.3 \times 10 ^ { 10 } h ^ { -1 } M _ { \sun } .
The resulting V -band mass-to-light ratios for B0712+472 and B1030+074 , measured inside their Einstein ring radii , are \sim 10 h~ { } ( M / L ) _ { \sun,V } , slightly higher than values observed in nearby ellipticals .
For B1600+434 , the mass-to-light ratio is 48 h~ { } ( M / L ) _ { \sun,V } .
This high value can be explained , at least in part , by the prominent dust lane running through the galaxy .
Two of the three lens systems show evidence of variability , so monitoring may yield a time delay and thus a measurement of H _ { 0 } .