Focal plane position: Nominal 150 mm below A&G mounting face,
shift of mm possible from this position.
Field size: 20 arcmin unvignetted, 22 arcmin with 50% vignetting.
Image quality: At nominal focus on a flat focal plane, 1 arcsec
over a 10 arcmin field and 1.5 arcsec over a 20 arcmin field. For the
maximum shift of 759 mm in the focal plane position, on axis images