Addition on Progressive lens

[ilan1204]

Hi

1.) Does anyone know how the addition effects on the center thickness on a lens?

how can i calculate the CT if i have an progressive lens??
single vision lenses i allready can calculate but how much do i have to add to the CT if i have an addition of 2.00??

2.) How much do i have to add on the edge thickness if i have cylinder??

like SPH -4.00 CYL - 2.00 Axe 80 DIA 60 Base 4.00 index 1.5

how much is my edge thickness on AXE 80 now???

thanx
mike

[Fezz]

Hi

1.) Does anyone know how the addition effects on the center thickness on a lens?

how can i calculate the CT if i have an progressive lens??
single vision lenses i allready can calculate but how much do i have to add to the CT if i have an addition of 2.00??

2.) How much do i have to add on the edge thickness if i have cylinder??

like SPH -4.00 CYL - 2.00 Axe 80 DIA 60 Base 4.00 index 1.5

how much is my edge thickness on AXE 80 now???

thanx
mike

Whats the size of the frame?

[ilan1204]

hi fezz

lets say the frame size is

x = 50
y = 25
bridge = 18
pd = 60

i dont really need a specific result just wanted to know how much does i have to add to the ET if my cylinder is (x) and how much do i have to add to the CT if my addition is (x).

how do i calculate the CT and the ET in single vision lenses and progressive lenses.

thanx - mike

[Fezz]

Mike,

I am sorry that I don't quite get what your question is. I will post a link to Opticampus. This is a website of one of our residaent experts on Optiboard, Darryl Meister. It is a great resource. It has various optical calculators that may help you. I am assuming that you are doing your own surfacing. This information should be calculated for you. I would have to dust of my old textbooks to see if I can get some formulas that may help you. Hopefully someone much more knowledgeable than I can chime in and help. Again, sorry for not being much more help. Good luck!


http://www.opticampus.com/tools/calculators.php

[TLG]

Harry will be salivating when he reads this post...:)

[Clive Noble]

Hi

1.) Does anyone know how the addition effects on the center thickness on a lens?

how can i calculate the CT if i have an progressive lens??
single vision lenses i allready can calculate but how much do i have to add to the CT if i have an addition of 2.00??

2.) How much do i have to add on the edge thickness if i have cylinder??

like SPH -4.00 CYL - 2.00 Axe 80 DIA 60 Base 4.00 index 1.5

how much is my edge thickness on AXE 80 now???

thanx
mike

Shalom Mike / Ilan

The Opticampus lens thickness calculator is so helpful, I have been using it for years! BUT it only gives you thicknesses for S/V lenses and you can get an approximate answer from this also for PALS, enough to keep a Px happy

Your question asked for CT on a PAL.... do you mean the physical centre or the virtual optical centre after prism thinning is applied?

The material used is also important as are the PD and all measurements of frame, A. B, ED etc

By the way, I'm also from Haifa!

Best, Clive

[HarryChiling]

From the point where the progression starts on the lens to the bottom of the frame can be used as the diameter/2 of your lens in a simple sagittal equation, then use the add power + power of the lens int he 90 as the power of the lens. If you go below the minimum fitting height you could get a bit more sophisticated by using an equation such as:

Dx = power chang per mm
Add = Add power
min = minimum fitting height

Dx = min / Add

then use the start of the corridor to the bottom of the frame (again only if the lens is cut below the minimum fitting height).

P = power of add to use in equation
cor = begining of corridor to bottom of frame

P = Dx * cor

Now use the begining of the corridor to the bottoom of the frame as your lensdiameter in the sagittal equation and the new add + power in the 90 as the power. If you knew the inset of the lens you could further use that to compensate the power decentered from the 90 fro a slightly more accurate result, but it would probably be negligable. This would be the thickness without prism thinning. If you wanted to do the hickness and include prism thinning then you would also need to figure out the start or of the corridor to the top of the lens and use this as a seperate diameter/2 in a sagittal equation and then take the difference between the bottom half of your lens and the top half of your lens and use that in a prism thickness equation reworked:

t=base to apex difference in mm (additional base thickness)
d=diameter (frame B size in this occasion)
P=prism
n=index of material

t=d*P/100(n-1)
P=t*100(n-1)/d

Now you have the amount of prism thinning to make the top and bottom edges of your progressive even.

[ilan1204]

thank you very much harry i will try your formula and hope that i will get the result that i was looking for.
i am trying to make a little program in visual basic that calculate the ct/et of sv and progressive lenses.

i want to thank all members of optiboard this is one of the best forum board that i have seen.

very professional and quick answers from the members and lot of thanks to darryl !!! :)

[ilan1204]

shalom clive

i'm trying to get the geometric CT of the progressive lens.

and the ET of progressive lens and SV with cylinder (AXE)

you are also from haifa??

i am working in a factory in ACCO that produced FREEFORM, SV,.. lenses.
i produced lenses with the optotech CNC machine and thats why i am interested in the prozess of the lens parameter calculation.

thanx

[DragonLensmanWV]

One short answer that hasn't been mentioned here:
On that high of a minus lens, add power will not figure much into the edge thickness.
On a plus 4.00, you betcha a 3.00 add will be thicker than a 1.00 add for a given frame.

[ilan1204]

is there a formula to calculate it, dragonlensman??