Formula for calculating thicknesses

[Spex]

Does anyone have a formula for calculating center & edge thicknesses that takes into account lens material, lens power, frame specs, PD, etc.?

I am really looking for some software to do this but if I could get an accurate formula I maybe able to create a spreadsheet or basic program to do the calculations.

Thanks!

[Judy Canty]

Your best reference is the Optical Formulas Tutorial by Ellen Stoner and Patricia Perkins. It's a softcover book, not terribly expensive and one of the best I've used.

[Pete Hanlin]

If it is software you seek, check out the downloadable programs section of the OptiBoard. Our very own Darryl Meister has written a spreadsheet called "OpticsLite" that performs the calculations you require (and many more).

Otherwise, I believe you will need to calculate the sagittal depth of each surface of whatever lens you wish to estimate the thickness of and go from there. Part of calculation of sagittal depth will take into account the amount of decentration (to determine the diameter of the lens).

A somewhat more simplistic way of calculating thickness (which I use from time to time) is to actually DRAW the lens on paper. I calculate the radius of curvature for each surface, consider the minimum thickness I desire, and draw the lens using a compass (I have some templates for the flatter curves already made)- generally works pretty well for demonstration/estimation purposes.

Pete

[Darryl Meister]

I wrote an article for calculating lens thickness that is now in the OptiBoard archives, which you might also find useful.

Best regards,
Darryl

[Spex]

Thanks Judy, Pete, & Darryl for your suggestions. They are great.

Pete, what if you can't draw. But I may try your suggestion for demo purposes with customers.

Judy, I have located one of my optical books buried deep in my basement. It has a formula in it that I can use. But I would like to find a way to look at your book. I am going to call my local community college that has an opticians program & see if they have a copy I can look thru. I may still find it useful in the future.

Darryl, I have your OpticsLite program & really like what you did. Is there anyway to incorporate a thickness calculator with in the Rx & Multifocal Analysis that would take into account lens material or index of refraction? That is a great interface you did inside Excel. I like it very much!

I am experimenting with the formulae I have found within an Excel spreadsheet, & its working but I still think there are some factors missing. Like the sagittal depth mention by Pete. There is a formula in this book for that also. Now I just have to incorporate it within what I have.

Thanks again guys & gals!!!
Chris

[Darryl Meister]

Hi Chris,

Actually, within the Ray Tracing module the spreadsheet calculates lens edge thickness, center thickness, and weight for you -- by material. You just dial in the Rx, the minimum blank size of the frame, and select a lens material. You can also choose a base curve and some other stuff, if you want to get terribly accurate. By toggling the lens view button, it also shows you a cross-section of your lens -- so that you have an actual picture to look at.

Best regards,
Darryl

[Spex]

Hey Darryl, I see what you mean. It looks like this is what I was looking for. And it even gives you a graphic drawing of the lens thickness. That's great!!

Do I need to do anything else other than enter the lens information like choose the material, lens power, base curve, center thinkness (on + edge thickness), & lens diameter to come up with the correct edge (or center) thickness?
You don't need to enter anything like the pupil size, vertex distance, angle of view, etc., do you?
And what effect does the Asphere P-Value have on thickness?

Thanks again for letting me know about that. I think I will put my little attempt on hold & just refer to your program. I keep finding out that program does more & more. I am going to start using it more. Thanks very much for taking the time to produce it! I believe it was time well spent!

[Darryl Meister]

Hi Chris,

You can adjust things like the vertex distance and angle of view to examine the peripheral performance of the lens. The calculations for unwanted oblique astigmatism, power error, and distortion are computed for whatever angle of view you pick. (A reference angle of 30 degrees is generally chosen in lens design work.) You'll notice, for instance, that you can control the peripheral performance by changing the base curve. You can design a "best form" lens, for example, by choosing the base curve that minimizes the unwanted lens aberrations I mentioned earlier.

I would just leave "pupil size" alone. It's just for some more advanced and esoteric features that you probably won't need.

The p-value allows you to incorporate simple asphericity into the lens design. Leave it at 1 for spherical base curves. For plus-powered lenses that use flatter than best form base curves, use a p-value below 1. For flattened minus-powered lenses, choose a p-value above 1. Simply adjust the p-value (up or down) until the lens aberrations are minimized.

Best regards,
Darryl

[achilles]

Originally posted by Judy Canty:
Your best reference is the Optical Formulas Tutorial by Ellen Stoner and Patricia Perkins. It's a softcover book, not terribly expensive and one of the best I've used.

what is the isbn number???

[achilles]

Originally posted by Darryl Meister:
Hi Chris,

Actually, within the Ray Tracing module the spreadsheet calculates lens edge thickness, center thickness, and weight for you -- by material. You just dial in the Rx, the minimum blank size of the frame, and select a lens material. You can also choose a base curve and some other stuff, if you want to get terribly accurate. By toggling the lens view button, it also shows you a cross-section of your lens -- so that you have an actual picture to look at.

Best regards,
Darryl

Can you give some more info on the Ray Tracing module??
Where can we get it??
is it also available in Europe?

Thanks Achilles




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[Steve Machol]

Originally posted by achilles:
<FONT COLOR=#FF0000> Can you give some more info on the Ray Tracing module??
Where can we get it??
is it also available in Europe?

Thanks Achilles
</FONT>

Actually it's available right here in the OptiBoard Download directory. You'll need Microsoft Excel to run it. Here's the link:

Optics Lite (http://optiboard.com/files/opticslite.exe)



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OptiBoard Administrator

[Judy Canty]

ISBN 0-7506-9913-2
Optical Formulas Tutorial
Ellen D. Stoner and Patricia Perkins
Butterworth Heinemann Publishers

[achilles]

Thanks for your reply and help

achilles