On Tue, Jun 02, 2009 at 01:30:28PM -0700, Joseph McAllister scripsit: > And how can a reflex lens have 8 elements in 6 groups? My 2000mm ƒ10 > Celestron 8" has a mirror, and a secondary mirror. They must have packed > a few elements into the small barrel to magnify the image from a 6" > design to make it 2000mm.
Most modern catadioptric lenses have the focusing meniscus/objective lens (depending on whether Maksutov-Cassegrain or Schmidt-Cassegrain), the primary mirror, the secondary mirror, and then a stack of regular old refractive lenses in the optical path after the primary mirror. Removing the objective and the mirrors as single element groups, that gives the remaining stack 5 elements in 3 groups, which doesn't seem unreasonable for a lens stack intended to do fine focusing. -- Graydon -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
