Calculation the prism ring

**simonxu** · 02-04-2013, 09:38 AM

Hello,
Please help me :

Click image for larger version.

Name: Prism ring.png
Views: 165
Size: 33.7 KB
ID: 9429

For the attachment image,the prism ring generating/blokcing parameter is software calculated result. But I don't know how to calculation method .Pls help me!!!

Thanks for help!!!

**PRECISIONLAB** · 02-05-2013, 09:16 AM

Prentice's Rule Power x Decentration/10 So +4.00 x 5mm dec / 10 = 2.00 diopters prism Base In for decentration. The variance or additional prism of 2.47 is due to the index of plastic being 1.498 vs 1.53 for standrard prism calc's

**Rafael** · 02-05-2013, 03:59 PM

In your screenshot from RXPert you choose Single Vision and High Index Plastic, but why your Material Index is on 1.498? Check your settings.

Attached formula for Tilt Calculation. Hope this helps you.

Best Regards
Rafael

**simonxu** · 02-06-2013, 08:18 AM

Originally Posted by Rafael

In your screenshot from RXPert you choose Single Vision and High Index Plastic, but why your Material Index is on 1.498? Check your settings.

Attached formula for Tilt Calculation. Hope this helps you.

Best Regards
Rafael

Thanks for your help!
Material Index is on 1.498 is right, I found the Prism ring generating/ring is change by Blanks fornt curve and Blanks index and Blocking Diameter.
So, I need find formula to calculation the prism wedge angle( same the prism ring generating/ring for Rxpert).

Thanks !!!