(water rushing)
- Oy, mate.
Come and join me on the adventure of a lifetime,
where today we find the source of the optical swamp.
(upbeat music)
Hello, I would like to welcome you
to the Laramy-K OpticianWorks Training Center
where today we are, in fact, going to talk
about where that unwanted peripheral distortion
in a progressive lens comes from.
Now, make absolutely certain that every progressive lens
in your optical life comes from Laramy-K.
If you're watching me on YouTube,
please do hit the subscribe button down there in the corner.
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It sure does help us out.
No project that we have ever undertaken
in the two-plus years that we have been doing this
has given me more trouble than this one.
Let's see if we can't clear it up a little bit.
Where does the up opti-swamp
and the land of optical garbage come from?
If you are not familiar with those two terms,
we did some videos back a couple months ago,
those two there.
If you haven't watched those,
then by all means go ahead and do that
and then come back and join us.
I had two questions that I wanted
to answer through this video.
One was what kind of language,
what kinds of things would you like to hear
an optician tell a customer when they ask
why is there that peripheral distortion
in a progressive lens?
And there is no easy answer.
Hopefully, you'll develop something
out of this and what's to follow.
The other piece is the more optical, more mechanical piece
of where that distortion comes from,
and we get really close to answering that.
One, what would you say to a customer?
This may seem a little flippant, but it really isn't.
You can't have your cake and eat it too, right?
That's a good a good place to start
in answering that question.
What is the first rule of optical?
To get something, you have to give up something,
the golden rule of optics.
Number three, the more you ask of something
the less likely it will do them well, right?
It's like the Swiss Army knife.
Yes, it can do 140 different things,
all of them kind of poorly, and it weighs seven pounds.
Not really a very useful tool in reality.
A sports car is not an SUV,
and an SUV is not a sports car.
If you try to take your Ferrari down a jeep trail,
you're not gonna get very far.
If you try to take your SUV to the racetrack,
it's gonna go off and crash.
So you can't really combine things in that way,
and that is what you're asking a progressive lens to do,
some things that it really can't, right?
A progressive is a choice of vanity
and convenience over optics.
Never ever forget that.
Let's repeat it.
I'll get out of the way here.
A progressive lens is a choice
of vanity and convenience over optics.
It is a compromise lens.
It is a compromised lens.
I mentioned in the opening sequence
that this was the most difficult piece
that we have ever assembled,
and it turns out that there simply is no easy answer
to where the distortion in the peripheral
of a progressive lens comes from.
And oh, how we tried.
We have unprecedented access up and down the supply chain,
from the very top to the very bottom.
We asked everyone, and we never ever came close
to a really good solid answer and/or model of some kind.
The closest we got is a paper written by Darryl Meister.
Darryl was a genius at taking extraordinarily
complex optical concepts
and making them fairly user-friendly.
His paper is called
the Fundamentals of Progressive Lens Design.
There are two places that you can find that.
And Darryl did give us permission to use that
through the Laramy-K site.
And even in that paper, Darryl uses an executive trifocal
to begin explaining the concept,
and then when actually describing
how cylinder becomes the answer to blending those zones,
he uses a Plano front base curve with a cylinder
to show you how a progressive lens is designed.
Now what does an executive trifocal, that thing there,
and a Plano front base curve have in common?
Well, they have a straight line or straight lines.
Now, this is one of the things I picked up
from one of the industry people.
If you want to put two different optical mediums,
if you will, together,
the best way to do that is a straight line.
Taking, for instance, again the executive trifocal.
Look at it, right?
If you want a perfect, clean, crisp vision
from nose to temple or temple to nasal,
across a lens for distance, intermediate, and near,
that would be as close as you can get.
Now, it's hideous, right?
I mean, it's not optically very good.
It doesn't hold an AR coat.
They look terrible.
They're heavy.
They don't fit in a frame well.
But that is as close as you're ever going to get
from full-width, wall-to-wall, if you will,
clear distance, intermediate, and near.
Again, remember, a progressive lens
is a compromise lens and a compromised lens.
So nobody liked the look of that,
so we went to segmented lenses, right,
distance, intermediate, near.
For a straight-top trifocal, straight-top bifocal,
what do you have in common still?
A straight line dividing those.
You can see them.
There is a jump between them.
If I'm looking straight on, what have I done?
I've taken my shallowest curve, added a steeper one,
added a steeper one again
for my bifocal and my trifocal area,
leaving ledges, leaving lines, leaving things you can see,
giving you that little bit of image jump.
But what do people want?
People want this.
They want it to look seamless, beautiful,
and there is the advantage of having that smooth transition
between your distance, your intermediate,
and your near powers.
It's kind of nice that way.
So yes, progressive lenses are good for some things.
Let's dig into that just a little bit more.
How do we go from this or this to this?
All right indulge me for a moment.
Think of the nominal lens formula, right?
The nominal lens formula is the diopter power of a lens
is equal to its front curve
added to its back curve expressed as diopters.
I think we can all agree on that.
It's very basic.
It doesn't work for everything anymore,
particularly freeform progresses, etcetera,
but it's a really good thing to start with.
The nominal lens formula is not, well,
kind of sort of the power is equal to,
well, somewhere in the vicinity
of this curve plus that curve give or take a little bit.
All right, following me here?
All right, you have to have absolutes.
If my lens power for this person
to see clearly in the distance is a minus one,
and the front base curve of my lens design is a plus six,
I still need a minus seven, hopefully,
right about here where their I is for distance,
to get my minus one.
There's no way around that.
All right.
Then, if I have an add of a plus two,
I still need plus one in intermediate
and an additional plus one at near.
Where do we do that?
Generally on the front of the lens,
we add the segment, all right?
If I have a lined trifocal, that thing again,
when I have three distinct areas or edge to edge,
that's really easy to do.
If I want this to be invisible,
if I want these things to blend together and work smoothly,
the smoothly parts fairly easy,
the blending together, that's very, very hard to do.
Look at that trifocal, the executive trifocal one more time.
Where those different segments come together,
look at the ledge that has to be there,
has to be, right, for clarity.
For this to work,
you can't get past the nominal lens formula.
It has to be there.
Those curves have to exist.
If I blend them smooth, then somehow fill in that gap,
make them invisible, you're gonna have some issues.
Let's take a look at cylinder, and then we'll hit the bench.
We should all be very, very familiar
with the concept of a sphere.
It is an object like the top half of this ball.
It measures the same radius of curvature in every direction.
The second piece to lens design
is the cylinder or the spherocylinder lens.
A cylinder looks like this.
And a cylinder, it has a variable radius of curvature.
It's going to have a Plano.
It's going to have a primary with its steepness curve.
And if I lens clocked it,
absolutely every point between my primary and my zero
is going to have a different radius of curvature.
That's what makes a cylinder lens.
Now, the opti-swamp in the land
of optical garbage is unwanted cylinder.
You read it, you see it, you hear it.
Distortion in the periphery
of a progressive lens is unwanted cylinder.
What exactly does that mean?
I'm gonna take this, I'm gonna take that illustration
from Darrell Meister's white paper,
and we're gonna see if I can't help you a little bit more
with the visualization or conceptualization
of the idea of where cylinder becomes unwanted cylinder
which becomes distortion in the periphery of a progressive.
Now, this is very much
a visualization conceptualization piece.
I'm gonna show you a Plano base curve
that blends into a very fixed radius curve
for the ad power in a bifocal
which is how Darryl has it set up.
You can see it.
It's beautiful.
Of course, in reality all of those curves
are much, much more complex
and of course require extremely sophisticated modeling
to come even close to reducing that error.
Let's take a look at our executive trifocal
just one last time.
Notice the area where the different radiuses
of curvature are close to one another, almost touching.
Notice how as we leave that center line of the lens,
the ledge increases sharply.
In extremely simple terms,
we can think of that center line, number two,
as what becomes our progressive lens corridor.
We can think of the red and yellow edges, or ledges,
becoming unwanted cylinder
when we smooth them out or blend them.
Let's make a 3D model of Darryl's illustration
and see if we can't make that a little clearer.
Speaking of Play-Doh, I just wanted to show you
what it says on the side of the container,
which I think means that Play-Doh is not gluten-free.
And our Play-Doh is gonna work for two things today,
our 3D modeling and a gentle reminder
of the color spectrum.
One last time, there are three other videos
in this series about progressive lenses,
progressive lens design.
Please watch those in addition to this one.
Never forget that every optical lens
is a compromise in some way.
Single vision, lined bifocal, line trifocal,
executive, progressive.
I'm not picking on progressives here.
There are wonderful lens, take you from sunup to sundown,
everything in between.
They're super useful.
But like every other lens, they're also not perfect.
What's this all about?
It's about unwanted cylinder.
Here is my cylinder.
Remember, Plano one place, primary steepest curve,
variability and curvature across
the entire rest of its surface.
What are we going to be implementing
to create a progressive?
I'm gonna be implementing exactly one half
of that cylinder amount.
So what do I have?
I've got a Play-Doh cylinder.
There it is.
That looks quite a bit like that.
Now, if we take Darryl's example and we cut out
that and that,
look what happens when I put my cylinder in there.
Because he chose to use a Plano front base curve,
the Plano leading edge,
the flat edge of my cylinder matches there.
Because of the variability of the curvature of the cylinder,
it matches the curve of my bifocal,
my ad, my steeper curve down here.
That is how we blend the areas
between our different needs for distance, intermediate,
and near in a progressive lens cylinder.
Now remember, I've got my center line
right there where they touch.
That's where my decent optics are going to be.
That's where I'm gonna have my distance area out
until I start hitting that cylinder.
I have my narrow channel here, my corridor between them,
because this is also, of course,
happening on the other side, as well.
And then I've got that familiar shape that we all know
for our near power down below.
The source of the optical swamp
and the land of optical garbage.
Thank you so much for watching.
I'll see you again next week.