Power distribution across a toric lens and prentice rule

[alberto_correia]

I've made this software for an article I've publish on an optics portuguese publication.

Its purpose is to display the power distribution across the diferent axis of a lens and the prismatic power induce when the visual axis is decenter by a given distance and axis. (For example: when we read something at near distance, we converge and look down).

Try it, it is free for non-comercial use.

The autor isn't responsable for the improper or inadequate use of this software and disclaimes any responsability on its use. Use it only if your qualify for it and always interprete is results with professional judgement and caution.

The software needs mschart.ocx, which was not included becaused of the uploads limits. See if it works.

Visit www.contactologia.no.sapo.pt (http://www.contactologia.no.sapo.pt) and see other optics software. I'll try to translate all of the software on that site to english, as soon as possible.

[Bobie]

alberto_correia ,
Please inform me , when you have English version in your website.
You software not working with my PC and I don't know why.

Thank :D

[HarryChiling]

Nice software, the version of prentices rule you use in your program falls apart when the power is very low and gies an error when computing a plano lens, but overall I love the graphics in it.

[alberto_correia]

This particulary software supports both portuguese and english. Just run it and choose the language on the combo box in the window right side.

If your meant the entire site, there is a easy way to do it. Simply enter the site link in the google translator. Give it a try, I did and I think it works just fine.

If you meant the other software in the site, you'll be sure to tell about it. But there is no doubt I'll have some news soon.

Alberto Correia APLO 22

[alberto_correia]

Yes. I are right in deed. I'll sort it out and bring it back soon. It's an overflow error produce by a division by zero.

It is also true that this short version of the Prentice rule, produces significant error when approaching plano power. Since it is the situation where less problems arises, I admit I was a bit lazy with my choice of this prentice rule.

No problem. I'll fix it soon.

Thanks

[Bobie]

Thanks , alberto_correia :cheers:

[HarryChiling]

Was it written in Visual Basic?

Use the matrix form of prentices rule:

Z = 2x1 prism matrix
P= 2x2 power matrix
h= 2x1 decentration matrix (in cm)

Z=P*h

Prismhorizontal = y * Dfront * sin A * cos A + x (Dsphere + Dcylinder * sin2 A)
Prismvertical = y (Dsphere + Dcylinder * cos2 A) + x * Dfront * sin A * cos A

the "y" would be the vertical drop (in cm) and the "x" would be the inset or convergence (in cm)

[alberto_correia]

It was written in VB6.

Thanks for the equations. I'll exchange for these ones and post a new version here.


Raul Alberto de Correia Sousa

[alberto_correia]

Dfront stands for vertex distance (Dvertex) or lens front vertex power?

Raul Alberto de Sousa

[HarryChiling]

Dfront = front curve in diopters

The vertex change compensation would be done before the power matrix.

[alberto_correia]

Gotta it.

Thanks.

[alberto_correia]

Hello.

I finally had time to do some work with your equations.

"A" is the difference between the cylinder axis and the decentration axis?

[HarryChiling]

A = axis

[alberto_correia]

Finally, the new version is ready.

Many thanks to Harry Chilling for the equations.

There are some small improvements on the different decentration input.

Try it.

Alberto Correia

[alberto_correia]

In some cases, the program may ask for a specific file called mschrt20.ocx.

This is a microsoft control that draws graphic chart and it is used by my program.

Download it and copy/paste to c:\windows\system32 or to directory where the program is installed.

[alberto_correia]

next

[alberto_correia]

Minor correction, when graphing lens power with zero spherical power.

Enjoy.

Alberto

[alberto_correia]

Dfront = front curve in diopters

The vertex change compensation would be done before the power matrix.

Someone pointed to me, that a -3,00x150 with a 10 mm downards (270 degrees) decentration and a 6 D front curve in the equations you send me, results in a Px +2,25, Py -2,60.

Px is correct but Py isn't.

So I went back and deducted the equations myself, following the matricial method you used.

I'll present them in a equivalente power form (Sph Cyl x Axis):

Px=x(Sph+Cyl*(sin A)^2)+y(-cyl*sin A *cos A)
Py=x(-Cyl*sin A *cos A)+y(Sph+Cyl*(cos A)^2)

This could be equal to yours equations if Dfront stands for front vertex power.

Since the prism diopter is based on the assumption that the lens is placed in the prentice position, where the front surface is perpendicular to the incident ray, the prismatic decentration induced power shouldn't be dependent on this value.

Could it be so?

Cheers,
Alberto Correia

[alberto_correia]

This new version is based on prentice rules equations deducted from the power matrix for a thin lens multiply by the decentration matrix.

It assumes flat front curve perpendicular to the incident ray (prentice position). So, the results are in prisms diopters and not in centrad.

Enjoy.
Alberto Correia