Measurement of centre thickness and edge thickness of a plus lens.

[Win C]

I would like to know how difficult is it for the lab to measure the CT and ET of a specified plus powered lens given all frame size and pd measurements.

I recently asked a lab to give me the (smallest) CT and ET of a +5.50DS RX cr39 1.5 single vision plastic lens for a specific frame for comparison purpose with a stock lens. they seem not able to do it , or were reluctant to do it (maybe it's because the calculations are too complex).

i was wondering how easy / difficult is it to do these calculations.

Would love to hear from the experts.

[Bezza]

most surfacing labs are able to calculate centre and edge thickness by simply feeding the data into their surfacing software or into a simple spreadsheet, takes no effort at all really.

However if you wanna do it yourself, that too is pretty simple,
t=s1+e-s2 where t is the centre thickness, e is the edge thickness and s1 and s2 are the sags of the front and back curves respectively.

To find the sags of those curves for a given diameter, you could either look them up on a sag chart or calculate using s=r-SQRT(r^2-y^2), where r is the radius of curvature of the surface (r=1000n-1/F) in mm and y is half of the diameter of the lens.

Hope this is helpful

[Win C]

Hi,
appreciate your help.
I knew that lab is just being lazy. I am bringing my business somewhere else. ;)

[EyeFitWell]

When you call and talk to the customer service folks at a lab, they are (usually in my experience) not knowledgable of optics in the least. They are great at taking orders and most at my lab are quite plesant, but start talking optics with them and they go silent...
If you have questions like this in the future, try asking to speak with someone who actually works IN the lab. You might get a better answer!

[Bezza]

If you can provide me with the A and B measurements of the frame I can give you a pretty good idea of the thicknesses as I have written my own sag calculations spreadsheet....wont be as exact as using a frame trace and surfacing software but itll be pretty darn close.

[Darryl Meister]

You can also access an online thickness calculator at OptiCampus Thickness Calculator.

[Win C]

When you call and talk to the customer service folks at a lab, they are (usually in my experience) not knowledgable of optics in the least. They are great at taking orders and most at my lab are quite plesant, but start talking optics with them and they go silent...
If you have questions like this in the future, try asking to speak with someone who actually works IN the lab. You might get a better answer!

The customer service folks was helpful, tyring to solve my problem by asking the people in the lab. However, it's the people who works in the lab who is trying to make things difficult for her.

I heard in the background what the lab personnel told her:" Don't have to talk so much with them (ie me), they dont know anything. " Can you believe it? If anyone from singapore is reading this, the lab is Plasticplus.

[Jubilee]

Ahh... now if I heard that going on in the background.. then I would want to talk to the lab personell. Just so I could set them straight!

The calculators on Opticampus or the one the Harry C. wrote and has in the optiboard files work great! It is nice to be able to tell someone that exactly how much thinner a lens will be/or in some cases thicker since they decide to be cheap this year and only get the base material.

"Sorry, I don't want the transitions, ARC, or hi-index materials I got last time. I think they were over rated, so I will go basic this year"

Sure Mr. +4, who is sensitive to light and complained last year about streaking of lights while driving....