Bruce Griffiths wrote: > Bernd T-Online wrote: >> Bi-convex contours are more difficult to manufacture, as it is required >> that the symmetry axis of the upper and lower contour must coincide. >> Also other parameters become worse. For the BVA the manufacturability >> would also be much worse as it already is. >> >> Regards >> >> Bernd >> DK1AG >> > Bernd > > Whilst traditional optical edging techniques can easily remove any wedge > when both surfaces are convex, maintaining alignment of the "lens" axis > with respect to the crystal axes is another matter, at least when using > traditional surfacing techniques, with computer controlled surfacing > techniques even this can be done. > > With a planoconvex "lens" bias polishing or an equivalent technique can > be used to adjust the inclination of the plano surface with respect to > the crystal axes and this alignment is maintained during edging leaving > only axial thickness adjustments to be made. The etching process used to > remove cracks and defects after mechanical polishing is anisotropic > which may introduce further complications in maintaining alignment and > shape. > > Bruce
So Bruce, what source did you read that led you to change your original answer from --it's easy--, to --it's difficult--? (reference your quoted text below: > Bi-convex contours are more difficult to manufacture, as it is required > > that the symmetry axis of the upper and lower contour must coincide. > > That problem was solved over a century ago in optical lens manufacture. If the two surfaces are spherical, then such decentering is equivalent to adding a wedge, which is easily removed by optical centering and edging techniques. > > Also other parameters become worse. For the BVA the manufacturability > > would also be much worse as it already is. -Chuck Harris _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.