Is there such a formula? What kind of effect (mathematically) does an increase in base curve have on edge thickness.
It is called sagittal depth and good book to get is optical formulas by butterworth their web page is www.bh.com
Boy where is Darryl when you need him?!?!
Have you checked out his opticampus.com thickness calculator? It should be able to figure it out for you but it wont help much if you are not near a computer.
The Thickness Calculator will give you a pretty accurate edge thickness, though I don't currently allow you to specify the base curve separately (the code currently "guesstimates" a base curve based upon the power and index of the lens). I could provide the details of how to calculate thickness, but the equations can be tedious. I have an old article on the subject here:
http://www.optiboard.com/forums/showthread.php?t=12645
I'll do some analysis though, and give you an idea as to how much thickness variation you should expect by base curve.
Also keep in mind that the edge thickness of lens in a wrap frame will depend upon 1) How the lens is edged and 2) How the thickness is measured. For instance, edge thickness calculations using "sag" formulas and such calculate thickness assuming that you are measuring it parallel to the optical axis. In lens design and ophthalmic optics this is frequently referred to as z thickness. A pair of lens calipers, on the other hand, measures the edge thickness perpendicular to the two surfaces (or at least an "average" surface somewhere between them). This is frequently referred to as strap thickness (from the straps of a rimless mounting).
This difference becomes even more important for a wrapped lens, since the z thickness can be considerably greater than the strap thickness with steeper base curves.
Darryl J. Meister, ABOM
My Reflections polys came back with a slight base curve to them, but I am having them re-done with a slightly sharper curve. I'm -0.75 in both eyes. Any special instructions I should give to the lab guy regarding making the lenses/edges -- I'm not sure how knowledgeable about this stuff he is.
(y*y*f)/(2000(N-1)) from memory - that is the rough and ready formula (y being the radius)Originally Posted by eteman
Last edited by QDO1; 09-26-2005 at 02:56 AM.
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