Saturday, July 23, 2011
Lens Thickness Formula !
After reading my last post for the basic thickness calculator, I have received some mails were asking me for the formula to find the thickness. (In that post, the formula was hided from the users)
Here I am explaining how to find the estimated thickness of a lens before it makes. To find the thickness you need to know the power, index, diameter and the edge/ center thickness.
For plus power you have to consider the edge thickness and for the minus powers you have to consider center thickness. (usual range is 0.9mm to 2.00mm according to the index)
Thickness= [(1/2*Diameter)^2*Power / [2000*(Index - 1)]] + edge/center thickness
For instance, given a lens power of -3.75 D, a refractive index of 1.53, and a minimum blank size of 65 mm, with 1.50mm center thickness, then the thickness would be:
[(1/2*65)^2*3.75 / [2000*(1.53 - 1)]] + 1.50 = 5.24 mm
For the ease of use I have created an excel file, there you can enter all the input values for the result (fig. 1).
You can download this calculator from here : Download Link