- Hello and welcome back to our ongoing series
Let's Learn How To Use The Lensmeter.
Today is going to be kit number five,
and that is a pair of mounted progressive lenses.
(upbeat music)
You know what I am about to say,
and now for a brief whiteboard lesson.
Well today I'm gonna surprise you and say
it's not going to be all that brief,
but we are going to have a whiteboard lesson
before we jump back into actually working
with the lensmeter.
We've done enough stuff now that it's time to
kinda get back into a lesson and talk about some things
because we're gonna start working with progressive lenses.
I've touched on this a couple of times, cylinder form.
The very last series of lenses we do the loose ones
when I talk about layout or for finishing.
I'll talk about the plus minus cylinder form
in a little bit more detail.
It really just comes down to which way you turn the drum,
and I don't want to oversimplify it,
or confuse anyone,
but that really is it.
If you're turning the drum this way you're reading something
in plus cylinder form.
If you turn it this way you're reading it in minus.
And we'll cover that again in the end,
but 99.9% of us are doing stuff in minus cylinder form now.
That's why I show it to you in that way.
This series is of course called
Let's Learn To Use The Lensmeter.
It is not called let's learn how to do verification.
The steps for that are on the OpticianWorks website.
Eventually we'll cover them here in video form,
but we're not there yet.
It's very difficult to talk about the lensmeter
without touching on verification final inspection.
So you are going to get a little bit of it.
A little bit about power,
there are times when you want to always start
with a stronger lens.
The stronger lens in the 90th meridian.
We'll talk about that down the line.
For now, mid range prescriptions, bread and butter stuff,
right lens, left lens, right lens, left lens,
you're gonna be fine.
VI is vertical imbalance, there are times
when you put the lens into the lensmeter,
you get it centered up,
and then you switch to the left or the right sometimes,
and the other one, the other target is up here,
that's your vertical imbalance,
we'll talk about that in the next lesson.
About that axis.
By now you've spent enough time working with a lensmeter.
Particularly if you have the same model
that we're working with.
That when you look inside and you look at the reticle
you're gonna see that sweep of zero to 180 axis
along the top.
Your lensmeter may not have it at all.
Labs use a 360 degree grid system
that's divided into quadrants to do prism layout work.
That's what that axis is for.
If you've wondered why it doesn't line up
when you're in correct minus cylinder form,
and you've got everything set the right way,
and you're turning your power drum
and the axis is 90 degrees away
from where you think it should be.
That's why don't worry about that.
People that are just starting out with the lensmeter
just ignore the axis that's inside
or within a part of the reticle.
Almost everything we're gonna do with progressive lenses
is going to be based on a chart.
And charts come from the manufacturer
specific to each progressive lens design,
super important.
It is not a one size fits all.
Here is why.
The industry standard for the markings on a progressive lens
are the same.
The distance between these two points.
The distance from this horizontal line
to the fitting cross
to the distance circle is not consistent.
That moves by a millimeter, two millimeters, three, four,
sometimes five.
If you use the wrong chart to mark up a progressive lens,
your distance circle may not be in the correct place.
You're gonna be measuring the wrong area on the lens.
You're gonna get bad readings,
you're gonna get prism imbalance, not a good thing.
You need to use the appropriate chart.
But I have also placed a dimple
to mark the spot that you're going to want the lens stop,
the opening of the lens stop, to be right above,
or right below excuse me, the dimple right below it.
So that you're looking in the proper place.
Progressive lenses have what is called prism thinning,
and different ones have different amounts.
Because of that, it is not unusual for the target
when you place the dimple or the spot
above the fitting cross, the distance circle,
right in the lens stop opening just like it should be,
for the target inside to be displaced.
Not unusual at all, in fact it's kinda normal.
That is where your PCD, or your prism compensation device
comes into play.
That's when you take that PCD and you twist it and turn it,
and you can bring the target into the center
of the reticle again so that you can read things
just a little bit clearer or a little bit easier,
little bit simpler.
Nice part about a progressive lens
it is the industry standard and the correct method
to read the add power directly from the lens itself.
It's all about the chart, once you take your lens
you mark up the lens using the appropriate chart.
That's when you can check your power,
you can check your fitting height,
and your monocular patient PD,
and we'll go over that in a moment.
Because of the unique optics of progressives
what you see is not always what you get.
So don't become frustrated or don't think
that there's something wrong just because
what you see on your job order form
is not an absolute perfect match
for what you see in the lensmeter.
Just don't be surprised if there's a little play
in the power drum, little play on axis,
we already talked about the PCD.
You have to be a little bit forgiving
when you're doing inspection on progressive lenses.
Alright let's dig around
in our kits and find frame and lenses number five.
Let's make sure that it is marked
with the etched marking number five
so we know we have the right frame and lenses in our hands.
As I mentioned over on the whiteboard
I have placed a dimple on the front of this lens
as a reference point for you.
Obviously things that you get back from the lab
or you're trying to setup for finishing work
are not going to have a engraved dimple
on the front of the lens.
They will either have the painted temporary markings
as a reference point,
or you're going to have to use
the lens appropriate layout chart,
remark it yourself, and then head to your lensmeter.
Instructions on how to use these charts
and doing marking up are on the OpticianWorks website.
Right lens, right lens, right lens,
and there's a closeup of where I want that dimple to be.
That would place the distance area, the distance circle,
the distance area of this particular prescription,
in the proper place for reading.
I am told that I have a minus three
so I can rotate my power drum to minus three.
Told I have an axis of 78, I can rotate that around to 78.
I can turn my lensmeter on,
and I can look inside.
A little tiny tweak on power,
little tiny tweak on axis,
and as I mentioned it is not unusual
for the target to be displaced in a progressive lens
when it is placed properly in the lensmeter.
That's when we take our PCD,
and this looks like it's about one up.
So I can rotate my PCD,
prism compensation device to bring it from up here,
into the center.
This is not an extreme case,
sometimes these will five, six.
Sometimes you won't even see this
or cylinder lines in there.
They may be way out here some place.
So you need to use your PCD to bring it into the center.
But I just gave you a little bit so you get a feel for it.
And sure enough I've got beautiful sharp sphere lines
at minus, a little over minus three.
And at about 76, again a little tweak, tweak is not unusual
on a progressive lens.
It tells me I have -175 cyls
so lets see where I get closed cylinder lines.
And I get it at about 475, almost five.
Again not unusual for a progressive.
It's about right for the distance traveled
from a three to a 475.
There's no reason to mark anything up.
Your dimple will act as your mark,
or your reference point for your monocular PD
and your fitting height, both.
So we're looking good in the right lens.
Without moving my spectacle table
I'm going to move from my right to my left.
And this time I'm told I have -325,
and it says I have an axis of 115.
Set there and set there.
Looking inside, didn't move my PCD at all.
I'm still just about in the right spot.
And it tells me I have a quarter cyl.
Let's talk about a quarter cyl for a moment.
There are times when a quarter cyl is barely discernible.
Don't be surprised if a quarter cyl looks almost
like a sphere, it's not unusual.
So don't freak out, it's just gonna be
this tiny tiny little turn of the power drum.
Hopefully at a quarter turn, but it's not always.
And I've got good closed cylinder lines.
Next our job order form tells us that we have
an add of a plus 150.
As I mentioned on the whiteboard.
We're gonna read the add power directly off of the lens.
You're looking for are the numbers that represent the add.
And those might be spelled out like 150, 1.50, 15.
Every company does it a little bit different,
and that information on how you read that'll
be on your chart.
But what you need to do is find those markings,
and just simply read the add power off the lens.
That would leave us with checking our monocular PD
and our height.
Our height we can simply take our PD stick
and measure from the dimple to the bottom of the frame.
And I have got a beautiful 18 there.
And I have got a beautiful perfect 18 there.
Again like the charting we're not gonna get into
the nitty gritty of it,
but the chart is also used for checking your monocular PD's.
That's what that center grid is for.
You're gonna lay the frame on that center grid.
You're gonna use the bridge to line up
using the triangle.
So it's centered,
and you're simply going to read where the dimple
on the right, dimple on the left covers the millimeter ruler
and that's going to match, if it's made correctly,
your monocular PD.
Next time we're gonna get back into a single vision pair
with some vertical imbalance.
Introduce that concept, and a little touch on prism as well
because they're kinda the same thing.
So I will see you next week when we tackle kit number six.
(grunts)