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- Hello and welcome to the
Laramy-K OpticianWorks Training Center
where today we are gonna wrap up our four part series on
the Nominal Lens Formula or Basic Lens Design.
Worth repeating, since this is the last in our series,
as I mentioned in the first.
Because of the way the way lenses are now designed,
particularly Free Form,
the Nominal Lens Formula or the Basic Formula formula for
lens design is only a concept today.
But it's a really really important concept for you to grasp.
We've looked at the formula in a couple of different ways.
Today we're gonna wrap up with an extremely realistic
scenario that you may very well find on any exams
that you might take.
Where you have the drawing, front base curve,
your two curves on the back, and you will need
to determine DL or the lens power.
So let's work through that last example.
Are you ready?
Good. Let's wrap this up.
In the first in our series, we solved for our
front base curve, D1.
In the second in the series, we solved with having DL
and D1, what D2 would be.
The third one we just talked about thickness and
where that comes from.
And today we're gonna solve for DL when we have D1 and D2.
Out of all those scenarios, in some ways, this is
probably the one you would see on an exam of some kind.
You would have just this piece.
And it would ask you to determine DL,
the total power the lens would be.
Kinda the written prescription that you would
take off of this drawing.
So how do you do that?
Once again I almost said "this is simple", but
it kinda is, really.
Just follow the formula D1 plus D2.
D1: three plus eight minus
equals I have a minus five there.
If I take five plus
six point seven five
minus equals minus 175.
And if I have seven plus 550
minus is a plus 150.
So far I've got minus five, minus 175,
and a plus 150.
We're not done. We're not done here.
Remember these lenses are all set up with two curves on the
back, they're spiro cylinder lenses designed to correct for
astigmatism, so we're gonna have a cylinder amount.
We are in minus cylinder form.
Minus, minus, minus, minus, minus, minus.
We're on the back side of our lens.
We've got plus here.
We must be in minus cylinder form.
So we're gonna go minus, minus, minus.
What is the cylinder amount?
The cylinder amount is the difference between
these two numbers.
From eight to 10 I am two diopters steeper.
My axis would be determined by the written prescription.
I'd rotate that lens around to fill it, put my lens meter
dots on there, and cut the lens.
What is the difference between 675 and 775?
I've got a difference of one diopter.
My axis can be determined.
What is my cylinder amount?
675 to 550 is a difference of minus 125.
Axis could be determined.
That is solving for DL the power of the lens
when you have D1 and D2.
Use your calculator.
These are even available on your exams now.
Hopefully you learned something through our journey
through the Nominal Lens Formula/Basic Lens Design.
Used to be kinda common that we would call this
Toric Transposition, that seems to be a term that
has fallen out of favor, so one of those three
you'll find out there.
Thank you so much for watching.
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I will see you next week.