> on 11/29/01 8:36 PM, John M. Lovda ([EMAIL PROTECTED]) wrote: > > > What makes UD glass so special or expensive? Other L lens > attributes such as > > aspherical or flourite lenses are intuitively obvious since the > grinding, > > molding, deposition or crystal growing techniques are more technically > > complicated than a regular spherical glass lens. What's the > deal with low > > dispersion glass; do the rare earth additives cost a million > dollars an ounce? > > Is the glass so hard it takes longer to grind? Is it really > fragile and hard > > to handle with lots of scrap? Why can Tokina, Sigma or Tamron > put UD glass > > into a much cheaper lens? > > It's really expensive to produce large pieces of optical glass that are > suitable for use as camera lenses. The tolerances needed are extremely > narrow, and it's highly likely that production will vary between batches. > > Some of the glass needed in a lens cost more per ounce than gold > (and weigh > just as much too). > > Camera Lens News No. 5, available from Carl Zeiss' website, talks about > what's involved in producing a Tele-Superachromat 300/2.8 lens for > Hasselblad cameras. They said they could only produce 300 or so of these > lenses due to the very limited supply of optical glass which has the > characteristics needed for the lens. > > Note that in the IS super-telephotos, there are two large UD glass lens > elements. > > OTOH, the UD glass put into the cheap third-party lenses are used in much > smaller elements, and usually put in there for advertising > purposes. Take a > look at the Nikon 70-300 ED (which allegedly is a Tamron design). The ED > element is tiny. > > -- > John Chennavasin
Hi John, Good answers. Regards, Chip Louie * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
