Adam Maas wrote on 12.01.06 2:38: > Pal, have you shot with a USM or AF-S lens? There's no comparison in AF > performance. USM absolutely blows screw-drive AF out of the water unless > you have either an ultra-light lens (like a 50mm) or one of the very few > cameras with a truly massive AF motor like the F5. I simply could not > believe the difference in AF performance between my old *istD and Tamron > 28-75 f2.8 and the EOS 3 with a 28-105 f3.5-4.5 USM lens. The EOS was so > much faster I initially didn't believe my own eyes (Although some of > that likely has to do with having the same AF unit as the EOS-1D). USM > is needed in the Pentax line, badly. You were comparing AF performance of heavy optics of metal built non-IF f2.8 lens to light, plastic, IF-equipped f3.5-4-5 lens... In 2004 when we meet with Dario we compared AF speed of two identical lenses in good light - Sigma EX 70-200/2,8 - one mounted on Dario's *istD, naturally screwdriven AF, second one with HSM motor and mounted to Nikon D70. I can assure you that there was no significant difference in AF speed at all, I've got even feeling that *istD was somewhat faster, but I could be under some influence of AF motor sound in *istD :-) I hope Dario will read this and confirm my observations. The conclusion is, that if you have two mechanically identical lenses, than there will be little difference between USM and good classic drive. Two main advantages of USM are its quietness and possibility to manual tweak of focus (FTM - this is now available in new Pentax lenses as QSF too).
-- Balance is the ultimate good... Best Regards Sylwek
