Focal plane position: 56 mm above the D--plate mounting surface,
126.9 mm behind the rear element of the corrector. The range of focus
travel is about 25 mm.
Field size: 40 arcmin unvignetted, 52 arcmin with 50% vignetting.
Image quality: On flat focal plane at standard focus, 0.5
arcsec over a 40 arcmin field, 0.5--2 arcsec at extreme of focus travel.
25 mm.
0.5
arcsec over a 40 arcmin field, 0.5--2 arcsec at extreme of focus travel.
, 40 
m arcsec
.