A workman using tools calibrated for spectacle crown glass, n=1.523, is instructed to produce the lens
+3.50DS/-1.00DCx180 in toric form with a +8.50 base curve. After working the sphere curve he discoveres that, in error he had used glass of n=1.618. Which toric tool must be used to work on toroidal surface in order that the lens may have finally the correct power?
Thank you for any kind of help.
Sorry I don't have time to look up this formula but the front surface power comes out to +3.12. Someone will answer this. People who surface lenses do this all day.
Edit
Last edited by Wes; 01-10-2012 at 10:48 AM.
Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA
“As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein
Thank you.
If I messed that up, I'm sure someone will be along to correct me. And if I didn't mess that up, well, I'm sure someone will be along to correct me.
See?
Last edited by Wes; 01-10-2012 at 10:49 AM.
Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA
“As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein
I have checked the answers and they are 8.12 and 8.96 and I am stuck again.
The cylinder difference that's less than 1 diopter makes sense, but a back curve higher than the front curve resulting in a plus lens doesnt. Please recheck everything before I do any more work on this. Shall I assume the +8.5 base curve is meant as a 1.53 tooling curve?
Last edited by Wes; 01-10-2012 at 10:53 AM.
Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA
“As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein
I get roughly 5.50, 6.37. Too much to type or explain on smartphone.
Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA
“As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein
I have tried everything but I have never got close these answers. Thanks for trying.
Probably because those answers are wrong.
Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA
“As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein
The question is somewhat ambiguous. There is also a reference to working a sphere curve and then using a toroidal tool afterward (I am assuming that this question wasn't written 30 or 40 years ago for a spherical generator or a hand pan).
If we assume that base curve value of +8.50 D refers to the curvature of the lens in the "tooling" index of 1.523, the actual surface power of the base curve becomes (1.618 - 1) / (1.523 - 1) * 8.50 = +10.04 D when using a lens material with an actual refractive index of 1.618. Ignoring lens thickness, since none is mentioned, the back tool curves in the 1.523 tooling index would then need to be -5.54 DS / -6.38 DC (or the nearest available tool curves to these values).
I should add that my results confirm Wes's.
Best regards,
Darryl
Last edited by Darryl Meister; 01-13-2012 at 03:34 PM.
Darryl J. Meister, ABOM
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