"Eye-Point Trace Technology"

[skirk1975]

How does Shamir break all the blank size rules with Eye Point Trace Technology? How exactly does this work and is anyone else doing this? They seem to be able to accomodate any frame size with any PD. I've seen some impressive ones done and they measure fine. How do they do this?

[optical24/7]

Lenses are fabricated (ground FF) with decentration. ( PAL corridor is ground decentered) just like you can do with conventional grinding of a SV (to decenter the OC). You can't do this with any lens that has the PAL design cast (molded) on the front. ( though a few cast designs are molded decentered)

[Chris Ryser]

http://www.shamirlens.com/ecp/ecp.aspx

[Lee Prewitt]

It really is not the "Eye point technology" either. That is digital ray tracing. Why can they do it? It is in the FF manufacturing as optical 24/7 stated.

[sharpstick777]

Not all manufactures, even Free-form, allow their lenses to be decentered (or decentered much). There are three reason's for this:

RX range changes dramtically. You end with a situation when you decenter that some RX can be done in some sizes, but not all. Company's want a fixed list of RX's that can be done, or not. It keeps it simpler. Most opticians don't understand why their RX in their frame requires a thicker blank than is available.

Yield. When you block a lens off center you have a greater chance, even in free-form, of that lens coming out off power (usually with unwanted prism) and yield goes down. As Free-form becomes more cost effective, you will see more companies allow their lenses to be blocked off center.

Blank Size. We always think in Diameter, but blank thickness has a major component of how far you can decenter and how high of an RX can be done. Shamir uses thicker blanks than other companies. This has two effects, it allows a higher RX range and it increases yield by allowing a more even blade pressure on the blank. To save costs many manufactures use thinner and smaller blanks, which limit decentering and RX range but keep blank costs down.

[Laurie]

More on 'why they fit'...

Lee and Sharpstick are on target with the fact that it is the computer software that enables a PAL design to work in a frame that it did not before. Also, as Optical 24/7 pointed out, this cannot be done with a molded lens, as the design parameters are already in place.

To learn more, ask your Shamir representative about 'Freeframe Technology'. This applies to the question. Rather than calculating the drop and near inset based on the 'B' measurement/Datum Line in the Boxing System, they build the design from the nearpoint parameter. This requires a digital frame trace and monocular PD's and mono fitting heights. The software (prescriptor) can then calculate the parameters starting at the near, along the path of near convergence. They 'build it out from there', allowing more aviator options with steep nasal-cuts...without cutting off the add in the process. (yes, full disclosure, in addition to teaching optics I do educational seminars for Shamir)

: )

Laurie