Formula for finding the right lens width for your PD?
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RE
Jul 22, 2008, 12:38:29 PM7/22/08
to GlassyEyes
It would be nice if there was an online calculator where you could
enter your PD, and they would tell you what frame width and bridge
size would be ideal for you. Is there such a thing? Any way or formula
to figure it out yourself? I was trying to keep a smaller lens width
as I didn't want the lenses too thick, but now I see there are other
considerations for not going for too wide a lens if you have a smaller
PD.
enter your PD, and they would tell you what frame width and bridge
size would be ideal for you. Is there such a thing? Any way or formula
to figure it out yourself? I was trying to keep a smaller lens width
as I didn't want the lenses too thick, but now I see there are other
considerations for not going for too wide a lens if you have a smaller
PD.
IMQ
Jul 22, 2008, 2:24:03 PM7/22/08
to GlassyEyes
I think the reason there isn't going to be any calculator you
mentioned because there are no scientific evidences that show some
correlation between the PD and the face width, etc.
If you were to take a look at a sample of 100 people whose face widths
are the same, you probably have the PDs of these 100 people fall in
certain range, say 62-66. So it is not possible to create a calculator
to give precise frame width and bridge size, given the PD as an input.
On the other hand, if such calculator existed, opticians would be out
of work. Who needed them to pick your frames when the calculator can
do a much more precise job for you. :)
mentioned because there are no scientific evidences that show some
correlation between the PD and the face width, etc.
If you were to take a look at a sample of 100 people whose face widths
are the same, you probably have the PDs of these 100 people fall in
certain range, say 62-66. So it is not possible to create a calculator
to give precise frame width and bridge size, given the PD as an input.
On the other hand, if such calculator existed, opticians would be out
of work. Who needed them to pick your frames when the calculator can
do a much more precise job for you. :)
RE
Jul 22, 2008, 2:52:59 PM7/22/08
to GlassyEyes
Thanks, but for the best vision correction wouldn't it be prudent to
pick your lens width based on your PD. I had meant to say a calculator
that would pick your lens width, not frame width, based on the bridge
measurement and your PD. Frame width seems more cosmetic, while lens
width needs to be in a certain range for your PD, in order to have
your pupils centered as much as possible in the middle of the lens.
pick your lens width based on your PD. I had meant to say a calculator
that would pick your lens width, not frame width, based on the bridge
measurement and your PD. Frame width seems more cosmetic, while lens
width needs to be in a certain range for your PD, in order to have
your pupils centered as much as possible in the middle of the lens.
Chuck Knight
Jul 22, 2008, 6:17:04 PM7/22/08
to RE, GlassyEyes
I actually made a post similar to this, a while back. Wish I could find it...
The basic idea, with any lens, is not only for the optical center of the lens to be in front of your eyes, but also for your eyes to be relatively centered in each lens.
Let's take the easiest example...a circular lens. My PD is 61mm, so I would want the centers of the lenses to be 61mm apart. That means that the circles could be 61mm circles...but oops, there's that nose bridge that takes up some space. So, let's subtract the bridge dimension and see what we come up with.
You take the PD, subtract the size of the nose bridge, and come up with your "ideal" lens size. Since we're using a circular lens shape for this example, let me go find one.
http://zennioptical.com/cart/product.php?productid=467&cat=0&page=1
These glasses have a bridge size of 20mm. So, 61mm - 20mm = 41mm. The ideal circular lens size for me, for this design, is 41mm. Well, this frame has 43mm lenses...pretty close, huh?
It works the same way with rectangular, round, oval, triangular, or any other lens shape...it's just that the circle makes it easier to imagine, in the mind.
There is a problem with this formula, though...it's only theoretical. It doesn't take into account aesthetics...taste...style...trends...and lens shape. But, it does ensure that your pupils will be in the middle of the lens. And, because of that, it gives you a good idea of what size to start with.
Just for reference, I'm wearing a 48mm wide rectangular lens with a 20mm bridge, and it's "close enough" for me. It looks darned good, too.
-- Chuck Knight
The basic idea, with any lens, is not only for the optical center of the lens to be in front of your eyes, but also for your eyes to be relatively centered in each lens.
Let's take the easiest example...a circular lens. My PD is 61mm, so I would want the centers of the lenses to be 61mm apart. That means that the circles could be 61mm circles...but oops, there's that nose bridge that takes up some space. So, let's subtract the bridge dimension and see what we come up with.
You take the PD, subtract the size of the nose bridge, and come up with your "ideal" lens size. Since we're using a circular lens shape for this example, let me go find one.
http://zennioptical.com/cart/product.php?productid=467&cat=0&page=1
These glasses have a bridge size of 20mm. So, 61mm - 20mm = 41mm. The ideal circular lens size for me, for this design, is 41mm. Well, this frame has 43mm lenses...pretty close, huh?
It works the same way with rectangular, round, oval, triangular, or any other lens shape...it's just that the circle makes it easier to imagine, in the mind.
There is a problem with this formula, though...it's only theoretical. It doesn't take into account aesthetics...taste...style...trends...and lens shape. But, it does ensure that your pupils will be in the middle of the lens. And, because of that, it gives you a good idea of what size to start with.
Just for reference, I'm wearing a 48mm wide rectangular lens with a 20mm bridge, and it's "close enough" for me. It looks darned good, too.
-- Chuck Knight
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