# Thread: POW Wrap and Prism Calculations

1. ## POW Wrap and Prism Calculations

I know that 8 base Wraps require prism compensation to compensate for the prism created when you turn the lenses. But I cannot find a calculator to tell "how much" prism is required. The Opticampus calculator does not give a result for prism in wraps, it only adjusts sphere and cyl powers. Does anyone know the forumula? Or another website for one? Thanks...

2. Darryl let it slip here, one time, and I furiously copied it. I have it at work.

Suffice it to say that it's simply a variable of lens thickness and tilt.

Empirically, about 1/4 to 1/2 p.d. BI OD and OS does the trick.

3. Darryl's Spectacle Optics program will indeed give you the prism compensation amount along with compensated sphere and cylinder. You must provide rx, wrap, tilt, base curve, and, I believe, index. Try it out.

4. is the old 'one mm displacement per 2° of tilt' worth thinking about if you're going to adjust the optical center horizontally for the 'horizontal tilt'?

5. You'd be better served doing the wrap calc and determining the prism that way. Your suggestion is asking for trouble.

6. Originally Posted by Wes
Darryl's Spectacle Optics program will indeed give you the prism compensation amount along with compensated sphere and cylinder. You must provide rx, wrap, tilt, base curve, and, I believe, index. Try it out.
I checked Opticampus, as stated above, and went through the calculators there and I could not find one that gives adjusted prism based on wrap angle and power. The wrap calculator on Opticampus only gives adjusted sphere and cyl powers, no prism or decentration amounts.

7. Originally Posted by Wes
You'd be better served doing the wrap calc and determining the prism that way. Your suggestion is asking for trouble.
Yes, but where is the wrap calc? Its not on Opticampus as the one there does not provide prism amounts.

8. Originally Posted by drk
Darryl let it slip here, one time, and I furiously copied it. I have it at work.
Suffice it to say that it's simply a variable of lens thickness and tilt.
Empirically, about 1/4 to 1/2 p.d. BI OD and OS does the trick.
Drk, Could you please repost it? Thanks

9. Originally Posted by sharpstick777
Yes, but where is the wrap calc? Its not on Opticampus as the one there does not provide prism amounts.
Originally Posted by Wes
Darryl's Spectacle Optics program will indeed give you the prism compensation amount along with compensated sphere and cylinder. You must provide rx, wrap, tilt, base curve, and, I believe, index. Try it out.
http://www.opticampus.com/files/spectacle_optics.zip

10. Thanks, There it is! Nice Program Darryl, I am sure it involved a ton of work.

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