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 | This article contains material which may inform and [EMAIL PROTECTED] | may be quoted, printed, forwarded, or redistributed www.fobpro.com | as long as the original attribution remains intact. * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
