How do reading glasses work? Do they magnify?

[Optical]

I was having this argument at work.

Some claim that reading glasses work because they magnify small print.
They claim that reading glasses sold at drug stores are labelled in
terms of their "magnification power" or strength.

I was arguing that the goal of reading glasses is not to magnify, but to
move the focal point, and that they don't really perform any
magnification.

Who's right?

Do many people use the term "magnification" incorrectly when talking
about reading glasses?

[Louis Boyd]

Post by Optical
I was having this argument at work.
Some claim that reading glasses work because they magnify small print.
They claim that reading glasses sold at drug stores are labelled in
terms of their "magnification power" or strength.
I was arguing that the goal of reading glasses is not to magnify, but to
move the focal point, and that they don't really perform any
magnification.
Who's right?
Do many people use the term "magnification" incorrectly when talking
about reading glasses?

Try this test. Go to your local drug store and ask if they have any
binocular focal length reducers for sale. They'll probably look a you
like you're nuts. Then ask for magnifying glasses.

Saying a simple convex lens gives magnification in a college level
optics course would usually not be appropriate, though there are cases
where it would. Consider a simple slide projector.

Part of life is learning the vernacular use of words and phrases. What's
important, making yourself understood or using a scientific definition?

[Optical]

Post by Louis Boyd

Post by Optical
Do many people use the term "magnification" incorrectly when
talking about reading glasses?

Part of life is learning the vernacular use of words and phrases.
What's important, making yourself understood or using a scientific
definition?

My basic question was - do reading glasses perform any sort of
magnification (when worn on your nose such that the lenses are located a
fraction of an inch in front of your eyes) ?

The fact that reading glasses may be labelled as or in terms of
magnifiers is a side-tangent issue to my basic question.

I was trying to make the point that when you quickly move a pair of
reading glasses quickly on and off your nose, that they don't seem to
make any apparent change to the size of text that's held close to your
face, but they do change the focus of the text so that it's easier to
read.

So am I right - that referring to reading glasses as "magnifiers" is
technically not correct?

[Louis Boyd]

Post by Optical

Post by Louis Boyd

Post by Optical
Do many people use the term "magnification" incorrectly when
talking about reading glasses?

Part of life is learning the vernacular use of words and phrases.
What's important, making yourself understood or using a scientific
definition?

My basic question was - do reading glasses perform any sort of
magnification (when worn on your nose such that the lenses are located a
fraction of an inch in front of your eyes) ?
The fact that reading glasses may be labelled as or in terms of
magnifiers is a side-tangent issue to my basic question.
I was trying to make the point that when you quickly move a pair of
reading glasses quickly on and off your nose, that they don't seem to
make any apparent change to the size of text that's held close to your
face, but they do change the focus of the text so that it's easier to
read.
So am I right - that referring to reading glasses as "magnifiers" is
technically not correct?

Reading glasses only allow you to focus on an object when you move the
object closer to you're face or your face closer to the object.
"Magnification" can be either a physical increase in image size (as with
a slide projector) or an apparent increase in image size (as with a
telescope. Both are precisely measurable. Moving an object nearer is
also an apparent magnification with the magnification being the ratio of
the two distance to the lens, usually the lens of an eye or a camera.

You are correct that just inserting them in your line of sight at the
position of your eye (as with contact lenses) does not produce
significant magnification. I wear glasses with a +4 diopter
correction (250mm focal length). When looking at distant objects they
produce practically no apparent magnification. Without them everything
is simply out of focus even at infinity. They do give weak
magnification of nearby objects because the lens is not in the same
plane as the lens of they eye. The purpose of reading glasses however
is only to bring nearby objects into focus. The "magnification" comes
primarily from reducing distance at which objects come into focus.


More properly glasses lenses are rated in diopters, not "magnification"
though the terms are often used interchangeably in common use. The
diopter value of a simple lens is the reciprocal of it's focal length
in meters. For "normal" glasses the number will be in the range of
about +6 to -6 though larger numbers are possible. Prescriptions are
normally written in 1/4 diopter steps. (you won't find a 3.3 diopter
lens commercially it will be 3-1/4 or 3-1/2).

In common English language usage glasses with positive diopter ratings
are still called magnifying lenses. Your crusade against the common
language usage makes no sense to me. What you may think are
"magnification" numbers are likely to be diopters which are a correct
lens specification. The manufacturers marketing can call them anything
they want. It may be labeled as "magnification" instead of "diopters"
on the packaging as most non-technical US citizens and aliens don't have
a clue what the word diopter means.

[Salmon Egg]

Post by Optical
My basic question was - do reading glasses perform any sort of
magnification (when worn on your nose such that the lenses are located a
fraction of an inch in front of your eyes) ?
The fact that reading glasses may be labelled as or in terms of
magnifiers is a side-tangent issue to my basic question.
I was trying to make the point that when you quickly move a pair of
reading glasses quickly on and off your nose, that they don't seem to
make any apparent change to the size of text that's held close to your
face, but they do change the focus of the text so that it's easier to
read.

If you want to be technical about it, define what you mean by
"magnification." Better yet, define what you mean by "no magnification."

Bill

[Optical]

Post by Salmon Egg

Post by Optical
My basic question was - do reading glasses perform any sort of
magnification (when worn on your nose such that the lenses are
located a fraction of an inch in front of your eyes) ?

If you want to be technical about it, define what you mean by
"magnification." Better yet, define what you mean by "no
magnification."

By magnification, I mean an apparent change to the size of an object or
text held in front of your face. To "magnify", as in "to make larger",
without physically moving the object or text closer to your eyes.

There are people that believe that "reading glasses" have some inherent
magnification properties, or that they accomplish the task of making
text easier to read because they magnify the text, and that reading
glasses are labelled in terms of their magnification "strength" (1.0,
1.25, 1.5, etc) and that constitutes some sort of "proof" that they are
indeed performing some sort of magnification as an intrisic or necessary
aspect of their functionality.

I argue with those people, by trying to show them how the apparent size
of closely-held text does not change when reading glasses are quickly
moved in front of and away from the eyes, and they seem to not
appreciate that clarity of text is more significant compared to any
subtle change of text size when these glasses are worn.

[Salmon Egg]

Post by Optical
I was having this argument at work.
Some claim that reading glasses work because they magnify small print.
They claim that reading glasses sold at drug stores are labelled in
terms of their "magnification power" or strength.
I was arguing that the goal of reading glasses is not to magnify, but to
move the focal point, and that they don't really perform any
magnification.
Who's right?
Do many people use the term "magnification" incorrectly when talking
about reading glasses?

BOTH!

The lenses for reading glasses are converging or positive lenses. They
have many applications. They can be used as magnifying lenses of the
kind pictured being held by Sherlock Holmes. Weaker versions have been
used as reading glasses, and they move the image of what you are looking
at to focus on your retina. Stronger versions can be put close yo the as
with jeweler's loupes. These really are like reading glasses but you
bring what you are looking close to the eye.

Bill

[Optical]

Post by Salmon Egg

Post by Optical
Some claim that reading glasses work because they magnify small
print. They claim that reading glasses sold at drug stores are
labelled in terms of their "magnification power" or strength.
I was arguing that the goal of reading glasses is not to magnify,
but to move the focal point, and that they don't really perform
any magnification.
Who's right?

BOTH!
The lenses for reading glasses are converging or positive lenses.
They have many applications. They can be used as magnifying lenses
of the kind pictured being held by Sherlock Holmes.

I was not talking about using the lenses for anything other than being
worn on your nose.

I was trying to make the point that when you quickly move a pair of
reading glasses quickly on and off your nose, that they don't seem to
make any apparent change to the size of text that's held close to your
face, but they do change the focus of the text so that it's easier to
read.

Hence my argument that even though they're commonly referred to as
magnifiers or performing some sort of magnification or even labelled in
terms of magnifying power, they really don't seem to magnify as part of
their design specification (when used as reading glasses, as worn on
your nose with the lenses just a fraction of an inch in front of your
eyes).






Weaker versions have been

Post by Salmon Egg
used as reading glasses, and they move the image of what you are looking
at to focus on your retina. Stronger versions can be put close yo the as
with jeweler's loupes. These really are like reading glasses but you
bring what you are looking close to the eye.
Bill
--
An old man would be better off never having been born.

[Don Stauffer]

Post by Optical
I was having this argument at work.
Some claim that reading glasses work because they magnify small print.
They claim that reading glasses sold at drug stores are labelled in
terms of their "magnification power" or strength.
I was arguing that the goal of reading glasses is not to magnify, but to
move the focal point, and that they don't really perform any
magnification.
Who's right?
Do many people use the term "magnification" incorrectly when talking
about reading glasses?

Yes, the main use of "reading" glasses is to create a virtual object
that appears to be further away from your eye. In fact, with any kind of
eyeglasses the objective is to move the apparent object distance to a
distance your eye can focus at.

[Chuck Olson]

Post by Optical
I was having this argument at work.
Some claim that reading glasses work because they magnify small print.
They claim that reading glasses sold at drug stores are labelled in
terms of their "magnification power" or strength.
I was arguing that the goal of reading glasses is not to magnify, but to
move the focal point, and that they don't really perform any
magnification.
Who's right?
Do many people use the term "magnification" incorrectly when talking
about reading glasses?

Both are right. But it requires moving the reading glasses away from the
face to get the magnification effect. As typically worn, there is very
little magnification, but a whole lot of shift in the user's focus distance
from the face. The "power" of the reading glasses is simply "100 over the
focal distance in meters", where the focal distance is the distance that
parallel rays entering the lens are focused to a point, e.g. +400 indicates
a focal length of 0.25 meters or about 10 inches. To be used as a magnifier,
this lens would have to be held away from the face 10 inches or more, and
the text being magnified would have to be 10 inches or less beyond the lens.
Worn as reading glasses, the +400 lenses would bring the user's focus from
40 inches (longer than an arm's length) down to 8 inches (for reading very
small print). The focal distance of the lens can be determined by casting
an image of a far distant scene on a sheet of paper and measuring the
distance between the lens and the paper when the image is sharpest.

[David Combs]

In article <icm9vt$soj$***@news.eternal-september.org>,
Chuck Olson <***@REMOVETHIScomcast.net> wrote:
<snip>

Post by Chuck Olson
To be used as a magnifier,
this lens would have to be held away from the face 10 inches or more,

Very interesting. Please say some more (tutorial even) on that point,
what effect from the distance the lens is from the eye.

(Also, how far away for it to turn the perceived image upside-down?)

Post by Chuck Olson
and
the text being magnified would have to be 10 inches or less beyond the lens.

Yes, "10 inches or more" vs "10 inches or less".

THANKS!

Post by Chuck Olson
Worn as reading glasses, the +400 lenses would bring the user's focus from
40 inches (longer than an arm's length) down to 8 inches (for reading very
small print). The focal distance of the lens can be determined by casting
an image of a far distant scene on a sheet of paper and measuring the
distance between the lens and the paper when the image is sharpest.

David

[gr]

Post by Optical
I was having this argument at work.
Some claim that reading glasses work because they magnify small print.
They claim that reading glasses sold at drug stores are labelled in
terms of their "magnification power" or strength.
I was arguing that the goal of reading glasses is not to magnify, but to
move the focal point, and that they don't really perform any
magnification.
Who's right?
Do many people use the term "magnification" incorrectly when talking
about reading glasses?

To answer the question originally asked; do they magnify when placed on
the nose and used as eyeglasses; No.
The lens of the eyeglass "adds" itself optically to the lens in your
eye, and the resulting combination allows you to focus closer than you
could before, thereby allowing you to see it better.
gr

[Salmon Egg]

Post by gr

Post by Optical
I was having this argument at work.
Some claim that reading glasses work because they magnify small print.
They claim that reading glasses sold at drug stores are labelled in
terms of their "magnification power" or strength.
I was arguing that the goal of reading glasses is not to magnify, but to
move the focal point, and that they don't really perform any
magnification.
Who's right?
Do many people use the term "magnification" incorrectly when talking
about reading glasses?

To answer the question originally asked; do they magnify when placed on
the nose and used as eyeglasses; No.
The lens of the eyeglass "adds" itself optically to the lens in your
eye, and the resulting combination allows you to focus closer than you
could before, thereby allowing you to see it better.
gr

In technical optics, magnification is defined in terms of object and
image. Visually, magnification of an optical system is the factor of the
image the object forms on your retina compared to what it is without the
optical system. Unless a decent image is formed on the retina,
magnification is a meaningless term. The main purpose of reading glasses
is to provide a good image on your retina. Any magnification is a side
issue. You get what the optical system does,

For me to give you a magnification (number) describe the object and the
optical system use. I can tell you what the magnification is even if the
image on your retina is just a big blur.

Bill

[Helpful person]

Post by Salmon Egg

Post by gr

Post by Optical
I was having this argument at work.
Some claim that reading glasses work because they magnify small print.
They claim that reading glasses sold at drug stores are labelled in
terms of their "magnification power" or strength.
I was arguing that the goal of reading glasses is not to magnify, but to
move the focal point, and that they don't really perform any
magnification.
Who's right?
Do many people use the term "magnification" incorrectly when talking
about reading glasses?

To answer the question originally asked; do they magnify when placed on
the nose and used as eyeglasses; No.
The lens of the eyeglass "adds" itself optically to the lens in your
eye, and the resulting combination allows you to focus closer than you
could before, thereby allowing you to see it better.
gr

In technical optics, magnification is defined in terms of object and
image. Visually, magnification of an optical system is the factor of the
image the object forms on your retina compared to what it is without the
optical system. Unless a decent image is formed on the retina,
magnification is a meaningless term. The main purpose of reading glasses
is to provide a good image on your retina. Any magnification is a side
issue. You get what the optical system does,
For me to give you a magnification (number) describe the object and the
optical system use. I can tell you what the magnification is even if the
image on your retina is just a big blur.
Bill
--
An old man would be better off never having been born.

Visual magnification is defined as the angular subtense of an object
seen with an instrument divided by the angular subtense as seen at a
distance of 10 inches (the near point).

Hence a 10X eyepiece has a focal length of 25mm.

www.richardfisher.com

[Helmut Wabnig]

Post by Optical
I was having this argument at work.
Some claim that reading glasses work because they magnify small print.
They claim that reading glasses sold at drug stores are labelled in
terms of their "magnification power" or strength.
I was arguing that the goal of reading glasses is not to magnify, but to
move the focal point, and that they don't really perform any
magnification.
Who's right?
Do many people use the term "magnification" incorrectly when talking
about reading glasses?

How does a loupe work, the wellknown "magnifying glass"?

there are two operating modes:

distant from eye
near to the eye

the eyeglasses we wear operate in the second mode.

the formulas for the "apparent magnification" are different
in the two modes.


w.

[David Combs]

Post by Helmut Wabnig

Post by Optical
I was having this argument at work.
Some claim that reading glasses work because they magnify small print.
They claim that reading glasses sold at drug stores are labelled in
terms of their "magnification power" or strength.
I was arguing that the goal of reading glasses is not to magnify, but to
move the focal point, and that they don't really perform any
magnification.
Who's right?
Do many people use the term "magnification" incorrectly when talking
about reading glasses?

How does a loupe work, the wellknown "magnifying glass"?
distant from eye
near to the eye
the eyeglasses we wear operate in the second mode.
the formulas for the "apparent magnification" are different
in the two modes.
w.

PLEASE say (teach us) more about the distant vs near effects.

Thanks!

David

[Salmon Egg]

Post by David Combs

Post by Helmut Wabnig

Post by Optical
I was having this argument at work.
Some claim that reading glasses work because they magnify small print.
They claim that reading glasses sold at drug stores are labelled in
terms of their "magnification power" or strength.
I was arguing that the goal of reading glasses is not to magnify, but to
move the focal point, and that they don't really perform any
magnification.
Who's right?
Do many people use the term "magnification" incorrectly when talking
about reading glasses?

How does a loupe work, the wellknown "magnifying glass"?
distant from eye
near to the eye
the eyeglasses we wear operate in the second mode.
the formulas for the "apparent magnification" are different
in the two modes.
w.

PLEASE say (teach us) more about the distant vs near effects.
Thanks!
David

Instead of going into all the special cases, it is actually simpler and
easier just to understand the elementary imaging by optics. The
principles are the same for both modes. The key is to obtain a clear
real image of the object on the retina.

As an example, consider someone with clear vision at infinity who gets
+4 diopter reading glasses to read text. Now he can read text clearly at
a distance of 0.25 meters from his eyes. His 60 year old nearsighted
friends wants to try them on just out of curiosity. The friend, who no
longer has any accommodation, already can see text clearly at 0.25
meters. With the glasses, he will see clearly at a distance of 0.125
meters. When he tries to read with the glasses, he holds the text at
0.125 meters instead of his usual 0.25. He comments, "This is great. It
magnifies the fine print to double size?

So, are these glasses reading glasses or magnifying glasses? Could this
single pair of glasses be both?

Bill

[b***@gmail.com]

Post by Optical
I was having this argument at work.
Some claim that reading glasses work because they magnify small print.
They claim that reading glasses sold at drug stores are labelled in
terms of their "magnification power" or strength.
I was arguing that the goal of reading glasses is not to magnify, but to
move the focal point, and that they don't really perform any
magnification.
Who's right?
Do many people use the term "magnification" incorrectly when talking
about reading glasses?

I just picked up a page and put on my bifocals, that function as my reading glasses, allowing objects to be focused on at closer distances than would otherwise be possible. If I hold the page so that it is in focus with my glasses on (looking through the part at the bottom designed for close work) and then raise the glasses with my other hand, keeping the paper in the same position, the print becomes fuzzy, and very very slightly smaller. My point is that while no one can tell someone else precisely what he sees, that based on my experience that I disagree with your observation as to what takes place.

The tops of my lenses are designed to compensate for my being myopic and so they are ground to negative diopters, and when I do the same test, looking at something in the distance, it appears smaller and in sharp focus compared to looking at it without my glasses. When I use a rifle scope, I can compensate for this loss of magnification by mounting a positive diopter lens on the scopes eyepiece, and refocusing it to the resultant shorter focal length by screwing it to a point of less extension (forward of its previous position) on the scope. There is some loss of eye relief, but not so much that it is a problem.

[j***@gmail.com]

Post by Optical
I was having this argument at work.
Some claim that reading glasses work because they magnify small print.
They claim that reading glasses sold at drug stores are labelled in
terms of their "magnification power" or strength.
I was arguing that the goal of reading glasses is not to magnify, but to
move the focal point, and that they don't really perform any
magnification.
Who's right?
Do many people use the term "magnification" incorrectly when talking
about reading glasses?

Kendra joined the chat
Kendra
How may I assist you?
john wright
I wear reading glasses with 2.25 diopter with a focal lenth of 12". They work fine for household chores, cooking, reading. When I play my violin, the music is 28" away and usually the notes and staff and words are out of focus and too small. I bought several of you magnifiers from Amazon to try them out, but they only made the music at 28" more out of focus, so I sent them back. As a violin player the focal length has to be 28" to get the violin and bow between me and my music stand. which product do you have for the violin players delema.
Kendra
Hazuki Magnifying Glasses come in two different focal lengths. The first starting at 1.6 (For close-range activity; 30-40 CM)Hazukis.The high magnification is suited for close-range, detailed tasks, such as reading, nail art, or crafting, making that fuzzy menu easy to read and that hard-to-see needle easy to thread. The second is our 1.32 (Long Focal Distance; 50-70 CM) Hazukis. The long focal distance allows for a natural posture enabling PCs, smartphones, tablets, or video games to be used comfortably.
Is there anything else I can assist you with?
john wright
So this does not answer my question,...I need a magnifier that makes an object at 28" focal length from my eyed magnify one and one half times bigger and be in focus
Kendra
I would recommend the 1.32 magnification
john wright
So the music needs to be magnified 1 and 1/5 to 2 times bigger, and be in focus at 28". Regular reading glasses are for focus correction and not for magnification, I need both magnification and focus correction.
So your recommendation is to get magnification one and one third times bigger, but what does it do for focus at 28" from my eyes, remember I have to get a violin and a bow in there in order to be able to play the violin
Kendra
The 1.32 magnification is for long focal distance and magnifies things up to 160%
john wright
And how should I use these glasses, put them on over my reading glasses or use them by themselves.
How does that math work 1.32 is 160%, I don't get it
I would think that 1.32 is 1 times plus .32 times bigger or 32% bigger than 1 times biger
Kendra
Hazuki glasses are magnifiers not reading glasses so they do not equate to the same
john wright
To find the magnification level of a lens, simply divide its diopter by 4, and add 1. ... A 5-diopter lens = 5/4 + 1... or 1.25 + 1 = 2.25x. so you can see that diopter and magnification is directly linked by the formula above
Kendra left the chat
john wright
So my reading glasses at 2.25 diopter divided by 4 = a magnification of 0.56 +1 or a magnification of 1.56. So to even focus on a reading at 12 inches I would need one of your glasses at 1.56 or pretty close to 1.6 magnification. But when I tried one of your magnifiers for music it was more out of focus that with 2.25 glasses. I don't know what to do here
Kendra joined the chat
Comment submitted
Kendra
I am not sure how the magnification translates over
john wright
could you help me get an answer to my question. I don't know how magnification and focal correction work together, but I do know that if you put a 1.5 dioper lense over a 2.5 diopter lense you get a3.0 diopter effective lense. I have done that with lenses and paste on lenses to set up my own glasses for close up in the bifocal and focus at normal reading distance.
Kendra
Reading glasses help you to focus on letters. However, letters may still appear too small to read. Hazuki enlarges objects with no distortion. Therefore you can have wider and clearer view with less fatigue after long hours use. You can also use them with your reading glasses!
john wright
So I asked google what does a 2.25 diopter mean in magnification and she said, "This refers to the amount of curvature a lens will have. More curvature means a thicker lens, more magnification and a higher diopter number. To find the magnification level of a lens, simply divide its diopter by 4, and add 1. ... A 5-diopter lens = 5/4 + 1... or 1.25 + 1 = 2.25x."
So you suggest that I could use my 2.25 lenses to focus at 12" on the music and use your magnifiers to make the music larger so that I could recognize the words and notes. So I spend $40 each for two sets of magnifiers a 1.32 and a 1.6, and another kit with 5 different sets of interchangeable lenses in it. When I put these 1.3 and 1.6 mags over my glasses the music was so fuzzy I couldn't read the music. so I returned them. When I put the magnifiers on without my glasses, I could see bigger images at about 6" away from my face. so still no music reading solution. I kept a pair of the power mags for soldering small electonic components together, but I still need a magnifier, focussing setup for reading music with my violin in place. That is what I need your help with.
Kendra
We only have the 2 magnifications; close range 1.6 and long distance 1.32
john wright
I don't have an answer, but you were certainly patient. Thank you. Seems like a simple situation, but has certainly been hard to get an effective answer.
Kendra
I don't have much information as it relates to how the magnification translates beyond what we have available; as it compares to readers they are best used with your prescription or readers and can be worn alone however how it correlates to the information you have shared I cannot say with certainty how it goes hand and hand
john wright
You are very adroit and treated me well
Kendra
Can I assist you with anything else?
john wright
No thank you. I find an improvement in both size and focus of my music if I take my 2.25 readers and add distance between my eyes and the glasses lense. I add a special holder to the nose pads that move my glasses toward the music by about a 1.4". That both magnifies the image of the music and helps my eyes bring it into focus. My wife tells me I look more nerdy that usual with these modified readers, but I can see the music and it really improves my sight reading. So, I know there are improvements to be made, but I cannot find someone who know how to implement what I have found by trial and error and not look so nerdy. I have alternate glasses with higher and lower diopter, like 1.5, 2.0, 2.5, 2.75, 3.0 and 3.5 but none of these are as effective as the 2.25 with the modified nose pads. If you wear glasses with a positive diopter, you can carefully slip the glasses off your nose and toward the objective, and you can see it get larger and in better focus up to the point where the eye glasses are half way between your eyes and the objective, if you wish to see what I see in the experimentation with my glasses

[Quadibloc]

Post by Optical
I was having this argument at work.
Some claim that reading glasses work because they magnify small print.
They claim that reading glasses sold at drug stores are labelled in
terms of their "magnification power" or strength.
I was arguing that the goal of reading glasses is not to magnify, but to
move the focal point, and that they don't really perform any
magnification.
Who's right?
Do many people use the term "magnification" incorrectly when talking
about reading glasses?

Well, reading glasses contain convex lenses. So a strong pair of reading glasses
could be used like a magnifying glass.

But you're still right too.

For print held a certain distance from the eye, reading glasses don't increase
the angular size of the letters.

Instead, they take the small letters close to the eye, and form virtual images
of those letters, which are bigger in size, at a distance far away from the eye,
with the same *angular* size at the eye, so that they eye can bring the images
to a focus.

So they let you read the printing as you hold the book closer to your face.

Since the virtual image does have a larger linear size at its new position,
magnification does still take place, even though it isn't really what makes the
print more readable (unlike, say, looking at something with the aid of an opaque
projector, or through a microscope).

Thus, the distinction is complicated, and explaining it is tantamount to an
introductory course in at least Gaussian optics!

John Savard