The Sloan Digital Sky Survey 2.5-m telescope is unique with a 3 degrees field of view at f/5. The two-mirror optical design includes two transmitting correcting elements To avoid excessive central obstruction of the entrance pupil, a conical baffle is necessary in addition to the usual primary and secondary baffles. This conical baffle is suspended approximately midway between the primary and secondary mirrors. In addition, an exterior close-fitting wind and light baffle, not found on most modern telescopes, blocks rays at large angles from the field of view.

We present measurements of galaxy-galaxy weak lensing from 225 deg(2) of early commissioning imaging data from the Sloan Digital Sky Survey (SDSS). We measure a mean tangential shear around a stacked sample of foreground galaxies in three bandpasses (g', r', and i') out to angular radii of 600", detecting the shear signal at very high statistical significance. The shear profile is well described by a power law gamma(T) = gamma(TO)(1/theta)", with best-fit slope of eta = 0.7-1.1 (95% confidence). In the range theta = 10"-600", the mean tangential shear is approximately 6 +/- 1 x 10(-4) in all three bands. A variety of rigorous tests demonstrate the reality of the gravitational lensing signal and confirm the uncertainty estimates. In particular, we obtain shear measurements consistent with zero when we rotate the background galaxies by 45 degrees, replace foreground galaxies with random points, or replace foreground galaxies with bright stars. We interpret our results by assuming that all matter correlated with galaxies belongs to the galaxies. We model the mass distributions of the foreground glaxies, which have a mean luminosity [L(theta < 5")] = 8.7 +/- 0.7 x 10(9) h(-2) L-g'circle dot,1.4 +/- 0.12 x 10(10) h(-2) L-r'circle dot, 1.8 +/- 0.14 x 10(10) h(-2) L-i'circle dot, as approximately isothermal spheres characterized by a velocity dispersion a, and a truncation radius s. The velocity dispersion is constrained to be sigma(v) = 150-190 km s(-1) at 95% confidence (145-195 km s(-1) including systematic uncertainties), consistent with previous determinations but with smaller error bars. Our detection of shear at large angular radii sets a 95% confidence lower limit s > 140", corresponding to a physical radius of 260 h(-1) kpc, implying that the dark halos of typical luminous galaxies extend to very large radii. However, it is likely that this is being systematically biased to large value by diffuse matter in the halos of groups and clusters of galaxies. We also present a preliminary determination of the galaxy-mass correlation function, finding a correlation length similar to the galaxy autocorrelation function and consistency with a low matter density universe with modest bias.

The Magellan guider camera uses a low-noise frame transfer CCD with a digital signal processor based controller. The electronics feature a compact, simple design, optimized for fast settling times and rapid readout rate. The camera operates (nominally) at 20 degreesC with thermoelectric cooling. Multiple operating modes are supported, with software selectable binning, exposure times, and subrastering.