Thanks everyone for helping me about 4 weeks ago with my questions re
'progressive' lenses.

I am now ready for bifocals. The progressives are wonderful for garage
sales and the supermarket. I no longer have to get on my knees to read
phono album and book titles. They are useless for all other purposes.

I want to order some bifocals, and obviously I will use the same
prescriptions.
OD SP +0.75, Cyl -0.75, Axis 098, Read Add +2.5
OS SP +1.00, Cyl -0.50, Axis 110, Read Add +2.5

However, I would also like to order a pair for the computer. I use +1.5
reading glasses for the screen, and switch back and forth to +2.5 reading
glasses for reading. If I want bifocals that do the same thing (obviate the
switching) what numbers do I use? Where do I plug in the +1.5 value?

Any and all help greatly appreciated.

Ivan Vegvary

Ivan Vegvary writes:

I want to order some bifocals, and obviously I will use the same
prescriptions.
OD SP +0.75, Cyl -0.75, Axis 098, Read Add +2.5
OS SP +1.00, Cyl -0.50, Axis 110, Read Add +2.5

However, I would also like to order a pair for the computer. I use
+1.5 reading glasses for the screen, and switch back and forth to +2.5
reading glasses for reading. If I want bifocals that do the same
thing (obviate the switching) what numbers do I use? Where do I plug
in the +1.5 value?

Change both adds to +1.5, instead of +2.5.

Why: The spherical/cylindrical lens should correct your vision for
focusing at infinity. The additional positive refraction (the "add") is
specified in diopters, which is the inverse of the focal length in
meters. If you hold a lens of power d in diopters in front of your
infinity-focused eyes, you will then focus instead at 1/d meters. So a
+1.5 add will focus at about 1/1.5 = 0.67 meters, or about 2 feet, which
for most people is a suitable computer screen reading distance. Your
2.5 add let you read a book 1/2.5 = 0.4 meters, or about 16 inches, from
your face, suitable for books.

So whatever distance you want to sit from the screen, in meters, invert
that and specify it as the "add" number.

Rather than bifocals for the computer, you might consider single-vision
lenses so you're not tipping your head about to read the screen. For
that you would specify no add, and instead add 1.5 to the spherical Rx
numbers, that is, 2.25 and 2.50 instead of 0.75 and 1.00.

"Richard J Kinch" wrote in message
.. .
Ivan Vegvary writes:

I want to order some bifocals, and obviously I will use the same
prescriptions.
OD SP +0.75, Cyl -0.75, Axis 098, Read Add +2.5
OS SP +1.00, Cyl -0.50, Axis 110, Read Add +2.5

However, I would also like to order a pair for the computer. I use
+1.5 reading glasses for the screen, and switch back and forth to +2.5
reading glasses for reading. If I want bifocals that do the same
thing (obviate the switching) what numbers do I use? Where do I plug
in the +1.5 value?

Change both adds to +1.5, instead of +2.5.

Why: The spherical/cylindrical lens should correct your vision for
focusing at infinity. The additional positive refraction (the "add") is
specified in diopters, which is the inverse of the focal length in
meters. If you hold a lens of power d in diopters in front of your
infinity-focused eyes, you will then focus instead at 1/d meters. So a
+1.5 add will focus at about 1/1.5 = 0.67 meters, or about 2 feet, which
for most people is a suitable computer screen reading distance. Your
2.5 add let you read a book 1/2.5 = 0.4 meters, or about 16 inches, from
your face, suitable for books.

So whatever distance you want to sit from the screen, in meters, invert
that and specify it as the "add" number.

Rather than bifocals for the computer, you might consider single-vision
lenses so you're not tipping your head about to read the screen. For
that you would specify no add, and instead add 1.5 to the spherical Rx
numbers, that is, 2.25 and 2.50 instead of 0.75 and 1.00.

Richard, thank you for your insightful reply. However, I want to be sure
that we are talking about the same thing.

I often have to do computer work (1.5 reading glasses work fine) while at
the same time I am making entries from a hand held manual or drawing. For
that I have to take off my computer glasses (1.5) put on my reading glasses
(2.5) read a sentence or dimension, replace my computer glasses and make a
keyboard entry. I was hoping to find a bifocal that will allow me to do
both with one set of glasses. Please advise.

Thank you
Ivan Vegvary

"Ivan Vegvary" wrote in message
...

"Richard J Kinch" wrote in message
.. .
Ivan Vegvary writes:

I want to order some bifocals, and obviously I will use the same
prescriptions.
OD SP +0.75, Cyl -0.75, Axis 098, Read Add +2.5
OS SP +1.00, Cyl -0.50, Axis 110, Read Add +2.5

However, I would also like to order a pair for the computer. I use
+1.5 reading glasses for the screen, and switch back and forth to +2.5
reading glasses for reading. If I want bifocals that do the same
thing (obviate the switching) what numbers do I use? Where do I plug
in the +1.5 value?

Change both adds to +1.5, instead of +2.5.

Why: The spherical/cylindrical lens should correct your vision for
focusing at infinity. The additional positive refraction (the "add") is
specified in diopters, which is the inverse of the focal length in
meters. If you hold a lens of power d in diopters in front of your
infinity-focused eyes, you will then focus instead at 1/d meters. So a
+1.5 add will focus at about 1/1.5 = 0.67 meters, or about 2 feet, which
for most people is a suitable computer screen reading distance. Your
2.5 add let you read a book 1/2.5 = 0.4 meters, or about 16 inches, from
your face, suitable for books.

So whatever distance you want to sit from the screen, in meters, invert
that and specify it as the "add" number.

Rather than bifocals for the computer, you might consider single-vision
lenses so you're not tipping your head about to read the screen. For
that you would specify no add, and instead add 1.5 to the spherical Rx
numbers, that is, 2.25 and 2.50 instead of 0.75 and 1.00.

Richard, thank you for your insightful reply. However, I want to be sure
that we are talking about the same thing.

I often have to do computer work (1.5 reading glasses work fine) while at
the same time I am making entries from a hand held manual or drawing. For
that I have to take off my computer glasses (1.5) put on my reading
glasses (2.5) read a sentence or dimension, replace my computer glasses
and make a keyboard entry. I was hoping to find a bifocal that will allow
me to do both with one set of glasses. Please advise.

Thank you
Ivan Vegvary

OK, add 1.5 to the main prescription and then make the bifocal only +1. YMMV
but I have the same issue, I'd go +1 on the main prescription and have +1.5
on the bifocals. Means the computer has to be 6 or 8 inches farther away

OD SP +2.25, Cyl -0.75, Axis 098, Read Add +1.0
OS SP +2.50, Cyl -0.50, Axis 110, Read Add +1.0
for your request.


Karl

Richard J Kinch wrote:
Ivan Vegvary writes:

I want to order some bifocals, and obviously I will use the same
prescriptions.
OD SP +0.75, Cyl -0.75, Axis 098, Read Add +2.5
OS SP +1.00, Cyl -0.50, Axis 110, Read Add +2.5

However, I would also like to order a pair for the computer. I use
+1.5 reading glasses for the screen, and switch back and forth to +2.5
reading glasses for reading. If I want bifocals that do the same
thing (obviate the switching) what numbers do I use? Where do I plug
in the +1.5 value?

Change both adds to +1.5, instead of +2.5.

Why: The spherical/cylindrical lens should correct your vision for
focusing at infinity. The additional positive refraction (the "add") is
specified in diopters, which is the inverse of the focal length in
meters. If you hold a lens of power d in diopters in front of your
infinity-focused eyes, you will then focus instead at 1/d meters. So a
+1.5 add will focus at about 1/1.5 = 0.67 meters, or about 2 feet, which
for most people is a suitable computer screen reading distance. Your
2.5 add let you read a book 1/2.5 = 0.4 meters, or about 16 inches, from
your face, suitable for books.

So whatever distance you want to sit from the screen, in meters, invert
that and specify it as the "add" number.

Rather than bifocals for the computer, you might consider single-vision
lenses so you're not tipping your head about to read the screen. For
that you would specify no add, and instead add 1.5 to the spherical Rx
numbers, that is, 2.25 and 2.50 instead of 0.75 and 1.00.


I am currently looking at new glasses for the wife.
Her problem is that she can see fine without correction out to 20-24"
After that the world becomes a big blur.

What I tried to talk to the doc about was a pair of bifocals with
correction on top and none on the bottom, he looked at me like I was
nuts. I would think it was a more common thing than what he seemed to
think.

OD SP -2.75, Cyl -0.25, Axis 175
OS SP -2.75, Cyl -0.75, Axis 155

Someone have an idea? Other than a new wife....

--
Steve W.

In article ,
"Ivan Vegvary" wrote:

"Richard J Kinch" wrote in message
.. .
Ivan Vegvary writes:

I want to order some bifocals, and obviously I will use the same
prescriptions.
OD SP +0.75, Cyl -0.75, Axis 098, Read Add +2.5
OS SP +1.00, Cyl -0.50, Axis 110, Read Add +2.5

However, I would also like to order a pair for the computer. I use
+1.5 reading glasses for the screen, and switch back and forth to +2.5
reading glasses for reading. If I want bifocals that do the same
thing (obviate the switching) what numbers do I use? Where do I plug
in the +1.5 value?

Change both adds to +1.5, instead of +2.5.

Why: The spherical/cylindrical lens should correct your vision for
focusing at infinity. The additional positive refraction (the "add") is
specified in diopters, which is the inverse of the focal length in
meters. If you hold a lens of power d in diopters in front of your
infinity-focused eyes, you will then focus instead at 1/d meters. So a
+1.5 add will focus at about 1/1.5 = 0.67 meters, or about 2 feet, which
for most people is a suitable computer screen reading distance. Your
2.5 add let you read a book 1/2.5 = 0.4 meters, or about 16 inches, from
your face, suitable for books.

So whatever distance you want to sit from the screen, in meters, invert
that and specify it as the "add" number.

Rather than bifocals for the computer, you might consider single-vision
lenses so you're not tipping your head about to read the screen. For
that you would specify no add, and instead add 1.5 to the spherical Rx
numbers, that is, 2.25 and 2.50 instead of 0.75 and 1.00.

Richard, thank you for your insightful reply. However, I want to be sure
that we are talking about the same thing.

I often have to do computer work (1.5 reading glasses work fine) while at
the same time I am making entries from a hand held manual or drawing. For
that I have to take off my computer glasses (1.5) put on my reading glasses
(2.5) read a sentence or dimension, replace my computer glasses and make a
keyboard entry. I was hoping to find a bifocal that will allow me to do
both with one set of glasses. Please advise.

It's a reasonable combination to have computer glasses above and reading
glasses below in the same pair of bifocals.

Joe Gwinn

BQ340 writes:

For example how would I specify a pair
of bifocals that give my say 3X at 2'?

Eyeglasses do not do that.

Reader eyeglasses do not magnify per se; what they do is move the near
point (how close you can hold something in focus) closer to your eye.
The standard distance of 10 inches is considered normal closest reading
distance and could be considered 1X. Now someone with emmetropic but
presbyopic vision (focused at infinity but no accommodation to focus
closer like a younger person) will need a +10D (+10 diopter) lens (100mm
focal length) to see at 10 inches. This is also about the strongest
eyeglass Rx. A +40 diopter lens (25mm focal length) is about the
strongest simple magnifier possible, and this lets you focus on items 1
inch away, which is in effect a 10X magnification from the standard 10
inches. But at +40D you are into loupe magnifiers and not eyeglasses.

To have true magnification the lens system has to be away from your eye,
not a contact lens with zero vertex distance or eyeglasses with a small
vertex distance. This is why people with high-power prescription needs
want to have small lenses that can tuck closer to the eye; then the
world is not distorted bigger, just focused properly. A true simple
magnifier produces a larger virtual image of the subject at infinity
focus. But it has to be away from the eye to do so, otherwise you're
just changing the refraction of your eyeball (and its focus point), not
magnifying or minifying anything. Another way to think of this is to
observe that putting a lens directly on top of an object doesn't magnify
the object; a simple magnifier must be some distance in between both the
object and the observer.

If you really want things 2 feet away magnified by 3X, the device is
called a "telescope" and is made of multiple elements. One example is
the binocular scopes worn by surgeons and dentists, the simplest types
being little Galilean opera glasses that are compact but dismal. Another
is a stand-mounted operating microscope like a Zeiss OPMI (called a
microscope when it actually is a close-focusing telescope).

As a machinist you can improvise your own binocular "operating
microscope" from a $10 pair of import roof-prism binoculars. All that
is needed is to extend the travel of the eyepieces further back to bring
the close focus point within a few feet:

http://www.harborfreight.com/cpi/cta...emnumber=92442

Ivan Vegvary writes:

I was hoping to find a bifocal that will allow me to do
both with one set of glasses. Please advise.

Like another follow-up post says, add 1.5D to the spherical Rx, and specify
the bifocal adds to be 1.0D. Then you'll focus 2 feet straight ahead, and
16 inches down through the bifocals.

"Richard J Kinch" wrote in message
. ..
BQ340 writes:

For example how would I specify a pair
of bifocals that give my say 3X at 2'?

Eyeglasses do not do that.

Reader eyeglasses do not magnify per se; what they do is move the near
point (how close you can hold something in focus) closer to your eye.
The standard distance of 10 inches is considered normal closest reading
distance and could be considered 1X. Now someone with emmetropic but
presbyopic vision (focused at infinity but no accommodation to focus
closer like a younger person) will need a +10D (+10 diopter) lens (100mm
focal length) to see at 10 inches. This is also about the strongest
eyeglass Rx. A +40 diopter lens (25mm focal length) is about the
strongest simple magnifier possible, and this lets you focus on items 1
inch away, which is in effect a 10X magnification from the standard 10
inches. But at +40D you are into loupe magnifiers and not eyeglasses.

To have true magnification the lens system has to be away from your eye,
not a contact lens with zero vertex distance or eyeglasses with a small
vertex distance. This is why people with high-power prescription needs
want to have small lenses that can tuck closer to the eye; then the
world is not distorted bigger, just focused properly. A true simple
magnifier produces a larger virtual image of the subject at infinity
focus. But it has to be away from the eye to do so, otherwise you're
just changing the refraction of your eyeball (and its focus point), not
magnifying or minifying anything. Another way to think of this is to
observe that putting a lens directly on top of an object doesn't magnify
the object; a simple magnifier must be some distance in between both the
object and the observer.

If you really want things 2 feet away magnified by 3X, the device is
called a "telescope" and is made of multiple elements. One example is
the binocular scopes worn by surgeons and dentists, the simplest types
being little Galilean opera glasses that are compact but dismal. Another
is a stand-mounted operating microscope like a Zeiss OPMI (called a
microscope when it actually is a close-focusing telescope).

As a machinist you can improvise your own binocular "operating
microscope" from a $10 pair of import roof-prism binoculars. All that
is needed is to extend the travel of the eyepieces further back to bring
the close focus point within a few feet:

http://www.harborfreight.com/cpi/cta...emnumber=92442

Richard, thanks for the great explanation. After reading it 4 times, I
think I understand it. Isn't the internet wonderful?

Thanks again for your wisdom.

Ivan Vegvary

"Ivan Vegvary" wrote in message
...

"Richard J Kinch" wrote in message
. ..
BQ340 writes:

For example how would I specify a pair
of bifocals that give my say 3X at 2'?

Eyeglasses do not do that.

Reader eyeglasses do not magnify per se; what they do is move the near
point (how close you can hold something in focus) closer to your eye

snip

look for a special set of glassess called "maxTV" -- specifically these
things:
http://www.eschenbach.com/preview.php?pid=654

I bought a pair at Westec from Gesswein