Need help in figuring tools.

[SithRico]

So a colleague and I are debating on how to figure out the tools for a job. We only have one set of lenses that took close to a month to arrive. They are 1.75 base 1.50 add progressives. The true base is 1.78. The RX is as follows.

-13.25 +1.25 X 2
-12.75 +2.00 X 89

I believe we are suppose to use the back vertex formula. But replace with power and base curve to find the value for the back.

He says to just add the base to the power and then add the cyl to the sum and that is the curve.

From my ABO training which has been over 10 years, I know we have to compensate for index of refraction which simple math wouldn't give us the correct curve.

Anyone out there able to help?
Thank you.

[Quince]

I just plugged in a test job in Visual Lab and came up with:

L------R
-9.62 -10.50
-11.12 -11.37

I'm not sure if this is helpful or not, but if it is, I used Accolade 1.74 with an adjusted true curve and 65 PD.

[Don Gilman]

So a colleague and I are debating on how to figure out the tools for a job. We only have one set of lenses that took close to a month to arrive. They are 1.75 base 1.50 add progressives. The true base is 1.78. The RX is as follows.

-13.25 +1.25 X 2
-12.75 +2.00 X 89

I believe we are suppose to use the back vertex formula. But replace with power and base curve to find the value for the back.

He says to just add the base to the power and then add the cyl to the sum and that is the curve.

From my ABO training which has been over 10 years, I know we have to compensate for index of refraction which simple math wouldn't give us the correct curve.

Anyone out there able to help?
Thank you.

I got R 10.38-11.28
L 9.48-10.92
This accounts for a 0.04 pad comp so we are close

[SithRico]

I forgot to put in there that the customer insisting poly. So those are the lenses we have OPC on the box are
406200832 R
406200386 L
I know there has to be a formula to solve this. If any one knows.
This person hates any other materials. Even if they are free. Says nothing works like polycarbonate. If people would only truly listen to people who have experience in the field and not just generic material online.

[Quince]

I forgot to put in there that the customer insisting poly. So those are the lenses we have OPC on the box are
406200832 R
406200386 L
I know there has to be a formula to solve this. If any one knows.
This person hates any other materials. Even if they are free. Says nothing works like polycarbonate. If people would only truly listen to people who have experience in the field and not just generic material online.

New back curve reading:

L---------------R
-11.50 -12.62
-13.25 -13.75



Tools:

L---------------R
+14.75 Base +16.62
+17.75 Cross +18.75

[Kujiradesu]

RX
-12.00 -1.25 x092
-10.75 -2.00 x179

So knowing this (Tool curve= compensated power - true base curve)

How do you get the compensated power? (0.53/0.586)*power. (this is assuming the tools you are using have curves designed for old crown)

So for poly

0.90443686*-12.00= -10.85
0.90443686*-13.25= -11.99
0.90443686*-10.75= -9.72
0.90443686*-12.75= -11.53

True BC= +1.78


OD: -10.85 - 1.78 = -12.63
-11.99 - 1.78 = -13.77 ------> closest tool -12.62/-13.75

OS: -9.72 - 1.78 = -11.50
-11.53 - 1.78 = -13.31 ------> closest tool -11.50/-13.37

If youre interested: Understanding Lens Surfacing by Brooks PG 114-115.

[SithRico]

RX
-12.00 -1.25 x092
-10.75 -2.00 x179

So knowing this (Tool curve= compensated power - true base curve)

How do you get the compensated power? (0.53/0.586)*power. (this is assuming the tools you are using have curves designed for old crown)

So for poly

0.90443686*-12.00= -10.85
0.90443686*-13.25= -11.99
0.90443686*-10.75= -9.72
0.90443686*-12.75= -11.53

True BC= +1.78


OD: -10.85 - 1.78 = -12.63
-11.99 - 1.78 = -13.77 ------> closest tool -12.62/-13.75

OS: -9.72 - 1.78 = -11.50
-11.53 - 1.78 = -13.31 ------> closest tool -11.50/-13.37

If youre interested: Understanding Lens Surfacing by Brooks PG 114-115.

Thank you so much. I know this will probably happen again. I can refer to this. Took a screen shot to keep as a tool.
Appreciate it so much!

[Kujiradesu]

Glad you found it helpful.

Just a warning, this way of figuring tools is good enough for government work, but for most plus lenses it doesnt do a good job. Theres an extra bit of math that you need to account to do that work that i never got around to learning (i probably should). Also for plus lenses center thickness will change the tool too. So i can only vouch for this method for minus lenses.

[SithRico]

Glad you found it helpful.

Just a warning, this way of figuring tools is good enough for government work, but for most plus lenses it doesnt do a good job. Theres an extra bit of math that you need to account to do that work that i never got around to learning (i probably should). Also for plus lenses center thickness will change the tool too. So i can only vouch for this method for minus lenses.

I think if you use the back vertex formula/true curve formula that works for plus.
Those where what I was trying to use for this but wasn't getting any tools close to this.
I was in the 9ish range. I knew that a minus lenses needed higher curves though. That's what started the debate.