9 Replies Latest reply on Jun 19, 2013 11:02 AM by Carter West

    Aspheric lens - using formula in surface

    Carter West

      Hi all,

       

      I need to make two models of reading glass lens.  One is 1.75 diopter the other 2.5.  Client wants to use aspherical lens surface curvature due to limitataions of thickness.

       

      -help-

       

      He has provided the formula but I can't seem to get it to work.  I don't work often enough in the surface world and I know this is a factor in not seeing my errors.

       

      =R-(R^2-r^2)^0.5+Br^4

       

      Even if you can help without the formula and create 1.75 ashperical, then that would be great and using that example I can do the rest of the work.

       

      Many thanks in adance

        • Re: Aspheric lens - using formula in surface
          Harold Brunt

          This is my work horse:  (x^2/R)/(1+(1-(1+(K))*(x/R)^2)^.5)

           

          It is a formula for a Rho variable driven conic curve. X determines the start and end points; K is the Rho variable where 0 = circle, 0 > K > -1 = ellipse, -1 = parabolic, and K < -1 is hyperbolic; R is the radius of curvature. The formula gives me the freedom to change the curve type without deleting the sketch plus it adds hyperbolics. The formula driven sketch tool allows the curve to be constrained to construction lines in the sketch instead of having to manipilate the position in the interface.

           

          Defining your variables would help since I don't design eyeglasses....

            • Re: Aspheric lens - using formula in surface
              Harold Brunt

              ... I'm still thinking about this. If I understand the definition of diopter for eyewear lenses then it is the inverse of the focal length or for 1.75 it is about 541mm. The lens surfaces are going to be defined by the Radius of Curvature and the Conic Constant but the actual curve will depend on the lens material refractive index. Low density PC vs high density PC vs glass will make a difference. It seems like the optician/optometrist has given you a formula without defining at least a couple of the variables.

               

              Just for curiosity, what is the end use of the files? I use native SW sketch tools and the formula driven sketch for non-imaging optics applications such as diffuse surface reflectors or lenses for illumination. For imaging applications where the bpsline surfaces in SW are unacceptable I use an optical design add-in. The package I use is OptisWorks.

                • Re: Aspheric lens - using formula in surface
                  Carter West

                  Harold,

                  Thank you for the great help.  My purpose of this surface project is only for the need of prototype testing of a new frame design.  My client would like to start with the range of typcial 'reading' glasses of +1.5~+2.5 dioptre.  Using a plano convex convention we have a couple design factors that have me asking if the ashperical shape may allow me to be able to to stay within my constraints.  See the screenshot for my current limiting boundaries.

                  Lens Sectional.png

                  As you can see, the left edge (outside of glasses) is tailed off to a weakened thickness.  The lens index for the moment is 1.53(n), but once I figure out the correct shape I can then mill it out of polycarb and put in the frames. The project will then go to the folks for the actual lens shape and final lab testing.

                   

                  I'd like to upload the model, but I can't seem to find the icon to allow me to do that. Why do the simplest things always have to be changed?

                   

                  Thanks again

                  Carter

                   

                  Part file attached (thanks Patrick).  Two configurations