High index single vision lenses

[Darryl Meister]

But Zeiss as well as Hoya have FF designs that don't allow as much freedom to user-define base curve, which is in keeping within their design performance goals. I think that, for most Rxs, the differences between SV designs are far less significant to the wearer than one might think. Darryl, I welcome your input herre.

In my preceding post, above, I offered a qualified response to this. Unfortunately, many free-form lens manufacturers out there are not particularly forthcoming with the details of their lens design technology, so it may be difficult to say whether any two given free-form SV lenses should perform similarly or not.

Optimal lens recipes MUST include Abbe to be fully inclusive of all optical degradation factors. This, of course, is left out of all this talk in the differences between lens design optimizations. Also, as Rxs amplitudes climb, representative personalized measurements also become important

Sure. Although, since chromatic aberration cannot really be significantly reduced by the lens design, you don't necessarily need to include a correction term for it directly in the calculations, as long as you choose a merit or optimization function that minimizes the monochromatic aberration that contributes most to the interaction between the monochromatic and chromatic aberrations.

For instance, while designing the Tillyer Masterpiece lens for American Optical, John Davis devised a merit function that included a lateral chromatic aberration term. He called this function a "blur index." However, you could get the same lens design result by simply minimizing the monochromatic tangential error of the lens.

Best regards,
Darryl

[RKJ]

For instance, while designing the Tillyer Masterpiece lens for American Optical, John Davis devised a merit function that included a lateral chromatic aberration term. He called this function a "blur index." However, you could get the same lens design result by simply minimizing the monochromatic tangential error of the lens.

Best regards,
Darryl

I'm learning from listening. Darryl, I wonder if you would mind sharing a list of typical merit functions. I'm trying to understand the scope of design considerations.

[huashuo]

HOYA 1.67 or 1.74 hi index is your best bet . all the multi coats are much the same and if i remember rightly polycarbonate lenses dont come with an AR coating . you maybe able to get them surfaced knife edged , just ask the dispenser if this is possible , it isnt always . If you do avoid supra frames and go for full frames . the finish will look better . hope this helps

[Darryl Meister]

Darryl, I wonder if you would mind sharing a list of typical merit functions. I'm trying to understand the scope of design considerations

I can describe a few of the more common optimization criterion terms used in single vision lens design, which are fairly simple:

Minimum Oblique Astigmatic Error (or "Point-Focal" design):



Minimum Mean Power Error (or "Percival" design):



Minimum Tangential Error:



John Davis's Blur Index, discussed earlier, where C is the lateral chromatic aberration:



Minimum RMS Power Error (also known as the Dioptric Power Vector):



Note that these the terms rely primarily on the ray-traced tangential power error (F_T) and sagittal power error (F_S) from the desired prescription power at each point (x,y) on the lens.

Most commonly, the lens design process will manipulate the lens surface until a "least squares" merit function M of the following form is minimized:



Where E_i is one or more criterion terms, or the error result of the criterion term from the desired value, and W_i is the weighting for each criterion term. These terms are assessed at (x,y) points over the lens.

A lens designer or software tool will then attempt to minimize the value of the chosen merit function for all points over the lens. A cosmetic term can also be added to the merit function, such as a term to minimize the lens volume V out to the lens radius r:



So, for example, the weights associated with the optical criterion terms could get smaller at greater distances from the center of the lens, whereas the weight for the cosmetic term could get larger.

A good practical example of this stuff can be found, for instance, in US Patent 6,305,800, which describes a series of atoric lens designs and the various merit functions used to design them. You can download this from the USPTO website.

Modern progressive lens design relies on merit functions as well, although lens designers may incorporate a greater number of optimization criteria, considering factors such as gradients of surface astigmatism, skew distortion, and so on. Also, the process of minimizing the merit function becomes considerably more complex, requiring finite element method and similar mathematical techniques.

You might be interested in a slightly more advanced training presentation that I put together on ophthalmic lens design, which I presented to a class at the Pennsylvania College of Optometry several years ago. If so, just private message me with your e-mail address.

Best regards,
Darryl

[RKJ]

This is very cool. Thank you!

I believe every single question I had has been answered as completely as possible. Feels good. Thank You!