Results 1 to 11 of 11

Thread: Elliptical lenses= thinner lens ?

  1. #1
    OptiBoard Apprentice gsmahesh's Avatar
    Join Date
    Jul 2010
    Location
    Kuwait City, Kuwait
    Occupation
    Lens Manufacturer
    Posts
    35

    Confused Elliptical lenses= thinner lens ?

    Does the Elliptical lenses will reduce thickness? If it does, what is the logic behind it.

  2. #2
    Master OptiBoarder
    Join Date
    Jun 2008
    Location
    Seattle WA
    Occupation
    Optical Wholesale Lab (other positions)
    Posts
    3,137
    Please explain more, what do you mean by Elliptical?
    Beer is proof that God loves us and wants us to be happy ~Benjamin Franklin

  3. #3
    OptiBoard Apprentice gsmahesh's Avatar
    Join Date
    Jul 2010
    Location
    Kuwait City, Kuwait
    Occupation
    Lens Manufacturer
    Posts
    35
    elliptical means the lens will not be in round shape.
    eg: normal lenses can be 65mm or 60mm diameter but elliptical will be 65/60 or 70/60
    you can see it on this below pic.
    Click image for larger version. 

Name:	elliptical and round.jpg 
Views:	1853 
Size:	74.6 KB 
ID:	9405
    Zeiss always following elliptical shapes as their standard (doesn't matter what power is) for progressive lenses

  4. #4
    Master OptiBoarder mdeimler's Avatar
    Join Date
    Feb 2012
    Location
    Three Mile Island, PA
    Occupation
    Optical Retail
    Posts
    720
    Elliptical shaping is simply better/easier to edge, without slippage. Many frames now have smaller B measurements, and the uncut lenses are now reflecting this.

  5. #5
    Underemployed Genius Jacqui's Avatar
    Join Date
    Oct 2003
    Location
    Frostbite Falls, Mn.
    Occupation
    Optical Wholesale Lab (other positions)
    Posts
    7,417
    The LOH generators have had the ability to crib oval shapes for some time. The others may also have it.

  6. #6
    Underemployed Genius Jacqui's Avatar
    Join Date
    Oct 2003
    Location
    Frostbite Falls, Mn.
    Occupation
    Optical Wholesale Lab (other positions)
    Posts
    7,417
    There should be no difference after the lenses are edged, just when uncut.

  7. #7
    Master OptiBoarder
    Join Date
    Jun 2008
    Location
    Seattle WA
    Occupation
    Optical Wholesale Lab (other positions)
    Posts
    3,137
    The reason some manufactures use elliptical blanks is purely to reduce material costs, most of blank is lost in processing (surfacing first, edging second). The end product will be the same, just less is cut away because there is less to begin with.
    Beer is proof that God loves us and wants us to be happy ~Benjamin Franklin

  8. #8
    OptiBoard Apprentice gsmahesh's Avatar
    Join Date
    Jul 2010
    Location
    Kuwait City, Kuwait
    Occupation
    Lens Manufacturer
    Posts
    35
    I dont think cost reducing is only the reason. I have noticed that for the lenses which is near to 90degre axis and plus powers are thinner if we make it in elliptical diameter.

  9. #9
    Objection! OptiBoard Gold Supporter shanbaum's Avatar
    Join Date
    May 2000
    Location
    Manchester, CT USA
    Occupation
    Other Optical Manufacturer or Vendor
    Posts
    2,977
    Whether an elliptical shape will result in a thinner lens depends on how the lens thickness has been calculated.

    In the U.S., lenses are usually ordered along with either a tracing or a set of frame measurements, and it is left up to the lab to determine cutout, blank size, and thickness. In that case, the shape of the uncut blank is likely to be completely irrelevant, because lens thickness will have been calculated using the frame shape or dimensions.

    In Europe, it’s more common for opticians to order lenses by blank diameter. In that case, ordering an oval shape (e.g., 70mm x 60mm) rather than round (e.g., 70mm) may result in a thinner lens, at least for lenses having a plus power in the vertical dimension (including many progressives).

    With the advent of freeform and automated processing, many labs now require that a generated lens not have any knife edges, because a sharp edge may tear up the polishing pad, and conformable lap – so there may be a “minimum thickness at crib perimeter” specified, which has to be considered in the thickness calculation. In that case, the uncut shape again may impact thickness.

  10. #10
    Master OptiBoarder optical24/7's Avatar
    Join Date
    May 2006
    Location
    Tx.
    Occupation
    Dispensing Optician
    Posts
    5,386
    Shanbaum, how do you achieve an oval shape on a sphrical lens without cribbing, molding or using more asphericity in a given meridian (non-PAL)? With decentration? If it's with the latter, how would it be thinner than say knife edging the correct cut out diameter?

  11. #11
    Objection! OptiBoard Gold Supporter shanbaum's Avatar
    Join Date
    May 2000
    Location
    Manchester, CT USA
    Occupation
    Other Optical Manufacturer or Vendor
    Posts
    2,977
    Quote Originally Posted by optical24/7 View Post
    Shanbaum, how do you achieve an oval shape on a sphrical lens without cribbing, molding or using more asphericity in a given meridian (non-PAL)? With decentration? If it's with the latter, how would it be thinner than say knife edging the correct cut out diameter?
    You don't, without cribbing. When you order lenses by blank size/shape (per my example), it's almost certainly going to be cribbed to that dimension, and that's the dimension to which it's calculated. In that context, "cut-out diameter" is unknown - the presumption is that the ordering optician has figured it out (a presumption of which I'm skeptical, but it's what they do).

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Lens markings on SV poly lenses
    By cocoisland58 in forum General Optics and Eyecare Discussion Forum
    Replies: 11
    Last Post: 05-08-2011, 09:11 PM
  2. Are prices listed for lenses for a single lens or for a pair of lenses?
    By eyedoctor03 in forum General Optics and Eyecare Discussion Forum
    Replies: 23
    Last Post: 12-19-2010, 10:22 AM
  3. Is The New Trivex Lenses Thinner Than Aspheric Poly And Hi 1.67?
    By Florida Specs in forum General Optics and Eyecare Discussion Forum
    Replies: 19
    Last Post: 12-19-2009, 01:48 PM
  4. Why should the progressive Lens be added the thinner prism?
    By copland in forum Progressive Lens Discussion Forum
    Replies: 8
    Last Post: 06-12-2007, 12:17 PM
  5. Thinner Trifocal with Easy to clean AR
    By For-Life in forum General Optics and Eyecare Discussion Forum
    Replies: 12
    Last Post: 01-06-2007, 09:17 AM

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
OptiBoard is proudly sponsored by:
Younger Optics and Vision Equipment