Binoculars and light amplification

[davenn]

Supposed there was a compact fluorescent lamp 20 meters away. Using the 8X binocular viewing it, would your retina receive more blue light than using just naked eye? .

not sure why you would want to do that, but yes the lenses would have the effect of concentrating the gathered light into a smaller area
This would increase the apparent intensity that your eye sees through the optics compared to naked eye

do you intend making a habit of looking at white LED and CFL lighting through binoculars ?not really sure what the point is that you are trying to make

it was described way back earlier in the thread that lenses can concentrate lightD

 

[cube137]

not sure why you would want to do that, but yes the lenses would have the effect of concentrating the gathered light into a smaller area
This would increase the apparent intensity that your eye sees through the optics compared to naked eye

do you intend making a habit of looking at white LED and CFL lighting through binoculars ?not really sure what the point is that you are trying to make

it was described way back earlier in the thread that lenses can concentrate lightD

I'm asking so I'd be determined to know to avoid those blue light when using my binoculars. I use them mostly at a daytime looking at the mountains, skies, birds and buildings.. I want to avoid or lessen blue light that is scattered from the sky to reach my eyes.

A binocular is said to magnify light. When you look at touchscreen cellphone to look at photos.. and press zoom... there is no additional light that isn't there. In the case of telescope. There is really focusing of light.. so the term magnification may not be enough.. perhaps we must use other terms like.. hmm.. focal amplification via collected light density... I need other examples where when you focus something.. you not just magnify it.. but also amplify it... in the case of objective lens... the extra energy to amplify it comes from the additional light rays in the objective lens.. so magnification is not accurate.

 

[davenn]

When you look at touchscreen cellphone to look at photos.. and press zoom... there is no additional light that isn't there.

HUH ?? doesn't make sense

In the case of telescope. There is really focusing of light.. so the term magnification may not be enough.. perhaps we must use other terms like.. hmm.. focal amplification via collected light density

don't make up terms ... you have already been told several times that there is NO amplification ...
again ... amplification requires the input of additional power

the extra energy to amplify it comes from the additional light rays in the objective lens

what additional energy or light rays ? ... there isn't any
sorry, the rest of what you wrote doesn't make any sense in the physics worldDave

 

[cube137]

HUH ?? doesn't make sense
don't make up terms ... you have already been told several times that there is NO amplification ...
again ... amplification requires the input of additional power
what additional energy or light rays ? ... there isn't any
sorry, the rest of what you wrote doesn't make any sense in the physics worldDave

I think you may be right above. But I think some of us get wrong somewhere before.

It's like this. a 7x35 binocular.. there is 49X of light focus into a point (compare to our pupil). But it's subtending 7 times the angle on the retina. So...the light density is reduced by 49x!

So we are not really looking at 49X of the light intensity at the focal point.. it's reduced because its subtending 7 times!

Therefore when looking at a compact fluorescent lamp 20 meters away. You won't have more intensity of the blue light harming your eyes. It's same intensity as original. Is it correct.. or not.

 

[cube137]

You may well have a point as far as a single point is concerned. That was what I just bumped into in my last paragraph.
But we have to be careful here! if a point is really a point, something infinitely small, then how can we have any light from it at all?! Say the object emits so much light per square metre, how much light does it emit from a point of zero diameter and area 0 m²?
On the other hand, if the point does have a finite size, however small, then the light it emits is focused to another point of finite size, determined by the magnification of the lens system. So the light may be less or more bright per unit area.

The point I was thinking of in my final comment, was that for a very tiny source like a star light years away, the light is focused to a point which should be very small, but is limited by diffraction to a size much bigger than it should be. When this image is magnified the image point should still be very small and is still limited by diffraction to a similar size. In that case the greater amount of light collected by the telescope is indeed focussed to the same area that the smaller amount collected by our eye would be. Then the image is brighter.

When we abandon very tiny sources like distant stars and start looking at a leaf on a tree for example, we now get images whose sizes are determined by the magnification of the lenses, not just diffraction. There will be a total amount of light from a given area of the object and this will be concentrated or spread over the area of the corresponding area of the image

I think this is the issue of my entire thread. I'm talking daytime view. So when we look at leafs thru a telescope, and the objective is say getting 49 more light to a point. how big is that point? is the 49 X diluted by 49 X back to same brightness or is there a point at focal plane that is really 49 X bright? Or think of the parallel ray from zero angle (directly horizontal).. even the leaf image would have airy disc concentrated at the center at focal plane.. would this 49 X brighter than the pupil of eye or would the airy disc itself be subject to magnification and dilution too? This is what I want to know.

 

[Drakkith]

So when we look at leafs thru a telescope, and the objective is say getting 49 more light to a point. how big is that point?

The light from any point on the leaf will be spread out into an airy disk, the size of which depends on the optical properties of the whole system, including the eye.

is the 49 X diluted by 49 X back to same brightness or is there a point at focal plane that is really 49 X bright?

For an extended object, yes, the image through the telescope or binoculars is the same brightness as it is through the naked eye. For a point-like source, like a far away star, the brightness is generally increased since even after you magnify the image the object is still unable to be resolved as anything but point-like. (Just like Merlin explained in post #23)

Or think of the parallel ray from zero angle (directly horizontal).. even the leaf image would have airy disc concentrated at the center at focal plane.. would this 49 X brighter than the pupil of eye or would the airy disc itself be subject to magnification and dilution too?

The leaf doesn't have a single airy disc. Every point on the leaf has its own airy disc, and since there are an infinite number of points, there are an infinite number of airy discs. It is this overlapping pattern of airy discs that forms the image on your retina. When you magnify the image of the leaf, you magnify the pattern of airy discs, which spreads out the light.

Therefore when looking at a compact fluorescent lamp 20 meters away. You won't have more intensity of the blue light harming your eyes. It's same intensity as original.

Not necessarily. If the lamp is small enough, then magnifying its image won't spread the light out very much, so the intensity increases drastically, similar to how a point-like source acts.

Honestly if you're worried about blue light harming your eye, just buy a blue-blocking filter.

 

[cube137]

The light from any point on the leaf will be spread out into an airy disk, the size of which depends on the optical properties of the whole system, including the eye.
For an extended object, yes, the image through the telescope or binoculars is the same brightness as it is through the naked eye. For a point-like source, like a far away star, the brightness is generally increased since even after you magnify the image the object is still unable to be resolved as anything but point-like. (Just like Merlin explained in post #23)
The leaf doesn't have a single airy disc. Every point on the leaf has its own airy disc, and since there are an infinite number of points, there are an infinite number of airy discs. It is this overlapping pattern of airy discs that forms the image on your retina. When you magnify the image of the leaf, you magnify the pattern of airy discs, which spreads out the light.
Not necessarily. If the lamp is small enough, then magnifying its image won't spread the light out very much, so the intensity increases drastically, similar to how a point-like source acts.

Honestly if you're worried about blue light harming your eye, just buy a blue-blocking filter.

Of course I know every point of the leaf has its own airy disc (each parallel ray and angle makes one airy disc).. let's take one single airy disc. The angular diameter of the airy disc is said to be inversely proportional to aperture.. the bigger the objective lens.. the smallest is the angular size of the airy disc. Now going to the 49X of light converging into a point. Let's take the case of one airy disc. Does it mean the 49X of light intensity are spread into the diameter of one airy disc and diluted 49X? Let's take the target as an extended object like a leaf and not a star.

 

[sophiecentaur]

I can't help thinking that introducing the Airy disc into this discussion is not helping at all. We are at a more basic level than that - partly to do with the actual definition of 'Brightness'. Wiki (convenient but not 100%, I know) refers to it as (R+G+B)/3, which implies we are talking in terms of energy from a sub division (pixel) of an image or object and not the total energy being emitted by or received from it. Stars, being point sources, will have a brightness that's independent of the telescope magnification.

How does one design an optical system in which all the light in the naked eyes field of view is collected by the objective lens and it is not spread to different points in the focal plane

A good example of this is a well designed telephoto lens for a camera, in which the sensor is well positioned and the limiting pupil is large enough to produce uniform illumination of the sensor. But even some expensive lenses exhibit Vignetting (darkening of the corners of the picture), which is where all the off-axis light is not getting through the limiting pupil. It's a common problem with eyepieces that you can't see a thing if you move your eye slightly from side to side. But, of course, the pupil is much smaller.
I have to ask just how the direction(s) that the thread is taking is helping to further answer the actual question in the OP? We have dealt with the magnification / amplification question satisfactorily, I think. The link in the OP actually deals with all of this pretty well. Perhaps reading it again (plus the Brightness link) would sort out the problem.

 

[cube137]

I can't help thinking that introducing the Airy disc into this discussion is not helping at all. We are at a more basic level than that - partly to do with the actual definition of 'Brightness'. Wiki (convenient but not 100%, I know) refers to it as (R+G+B)/3, which implies we are talking in terms of energy from a sub division (pixel) of an image or object and not the total energy being emitted by or received from it. Stars, being point sources, will have a brightness that's independent of the telescope magnification.

A good example of this is a well designed telephoto lens for a camera, in which the sensor is well positioned and the limiting pupil is large enough to produce uniform illumination of the sensor. But even some expensive lenses exhibit Vignetting (darkening of the corners of the picture), which is where all the off-axis light is not getting through the limiting pupil. It's a common problem with eyepieces that you can't see a thing if you move your eye slightly from side to side. But, of course, the pupil is much smaller.
I have to ask just how the direction(s) that the thread is taking is helping to further answer the actual question in the OP? We have dealt with the magnification / amplification question satisfactorily, I think. The link in the OP actually deals with all of this pretty well. Perhaps reading it again (plus the Brightness link) would sort out the problem.

Ok. I'm just confused by the difference between sources as extended object and light sources. This is because in my daytime use of the binocular tracking birds in flight.. I can see many sunshines.. sometimes sunlight reflecting off shiny poles and windows.. so wonder how it magnifies in my focal point and affect my eyes.

Anyway. When you use a magnifying glass on paper. It burns.. so does it burn because the airy disc has so much light intensity or is it because the sunlight is spread to large area in the paper. I guess it is the former. Isn't it. Is there a test of this where the paper are detectors. Anyway. I learned in this thread there is a difference between sources as extended object (like leafs) and light sources (light sunlight reflecting off poles, etc). that is not in the original web link.

 

[Drakkith]

Now going to the 49X of light converging into a point. Let's take the case of one airy disc. Does it mean the 49X of light intensity are spread into the diameter of one airy disc and diluted 49X?

The basic idea to take away is that for an extended object the brightness of the object decreases with magnification. In this specific example, the increase in light-gathering ability of the binoculars over the eye is directly countered by the reduction in brightness by the increased magnification.

Ok. I'm just confused by the difference between sources as extended object and light sources. This is because in my daytime use of the binocular tracking birds in flight.. I can see many sunshines.. sometimes sunlight reflecting off shiny poles and windows.. so wonder how it magnifies in my focal point and affect my eyes.

They can behave like extended objects, like point sources, or somewhere between, depending on the details.

Anyway. When you use a magnifying glass on paper. It burns.. so does it burn because the airy disc has so much light intensity or is it because the sunlight is spread to large area in the paper.

The sunlight isn't spread to a larger area, it's spread to a smaller area. A magnifying glass is not a compound optical system and doesn't behave exactly like we've discussed here.

 

[sophiecentaur]

so wonder how it magnifies in my focal point and affect my eyes.

Of course it can hurt your eyes if you spend any time looking directly at the reflections. But our eyes can obviously cope with the occasional glimpse of the Sun, directly, or we would all be blinded by now. A good reflection from a mirror surface would be as bad as looking directly at the Sun with your telescope. You don't need me to tell you to be careful.
Have you actually been reading all the posts on this thread and your original link? You have been getting the same messages many times yet you don't seem to be accepting it. You can't always expect answers to be couched in precisely the same terms that you want. Just look for the meaning in all the above posts.

 

[cube137]

The basic idea to take away is that for an extended object the brightness of the object decreases with magnification. In this specific example, the increase in light-gathering ability of the binoculars over the eye is directly countered by the reduction in brightness by the increased magnification.
They can behave like extended objects, like point sources, or somewhere between, depending on the details.
The sunlight isn't spread to a larger area, it's spread to a smaller area. A magnifying glass is not a compound optical system and doesn't behave exactly like we've discussed here.

So for point sources, magnification won't increase the size.. and I assume, magnification won't increase the intensity either? So it's like the point sources are already using the objective lens as magnifier... right?

Now for the ultimate question. something I will never test.. what happens to the sun on the focal plane of the telescope.. do you consider the sun as composed of many point sources or an extended object?

 

[sophiecentaur]

So for point sources, magnification won't increase the size.. and I assume, magnification won't increase the intensity either? So it's like the point sources are already using the objective lens as magnifier... right?

Now for the ultimate question. something I will never test.. what happens to the sun on the focal plane of the telescope.. do you consider the sun as composed of many point sources or an extended object?

You have justified the points I made in my last post. A point source becomes an airy disc: already discussed at length. Magnification will not alter the energy falling on the image: already discussed.
The angle subtended by the Sun is about 0.5°. Is that a "point"? The Moon is about the same apparent size and we can see many features with the naked eye. That is definitely not a point. : We already discussed the idea of replacing a distribute source by a set of points so that would apply to the Sun, also.
I am sorry to appear grumpy but you really could do us the courtesy of reading what people have already written.

 

[cube137]

You have justified the points I made in my last post. A point source becomes an airy disc: already discussed at length. Magnification will not alter the energy falling on the image: already discussed.
The angle subtended by the Sun is about 0.5°. Is that a "point"? The Moon is about the same apparent size and we can see many features with the naked eye. That is definitely not a point. : We already discussed the idea of replacing a distribute source by a set of points so that would apply to the Sun, also.
I am sorry to appear grumpy but you really could do us the courtesy of reading what people have already written.

Ok. Thanks for all help. I bought a binocular over $1000 so just want to make sure I understand how not to damage my eyes :) As I use it spanning across the landscape.. each of the message here will echo in my mind... thanks again..

 

[Drakkith]

So for point sources, magnification won't increase the size.. and I assume, magnification won't increase the intensity either?

The size of the air disc will increase proportional to magnification, but a true point source will not increase in apparent size. For point-like sources, such as stars, their angular diameter does increase with increasing magnification, but when even the closest and largest stars are less than one-thousandth of an arc-second in angular diameter, far smaller than their airy discs, they don't appear to get any larger until you get a LOT of magnification and a LOT of aperture.

Now for the ultimate question. something I will never test.. what happens to the sun on the focal plane of the telescope.. do you consider the sun as composed of many point sources or an extended object?

All extended objects can be thought of as being composed of an infinite amount of point-sources.

Ok. Thanks for all help. I bought a binocular over $1000 so just want to make sure I understand how not to damage my eyes :) As I use it spanning across the landscape.. each of the message here will echo in my mind... thanks again..

Don't look directly at the Sun. Don't stare at bright reflections. Don't get caught peeping into people's windows. That's about all you need to be worried about.

 

[litup]

One thing about magnification Vs amplification: Magnification increases resolution by using lenses bigger than our eyes. Amplification only makes the image brighter through electronic means. The resolution stays the same. If you use a bigger lens you get both increased resolution and brightness but electronics can make that image brighter yet but does not help resolution, the ability to separate two close spaced objects.

 

[jbriggs444]

One thing about magnification Vs amplification: Magnification increases resolution by using lenses bigger than our eyes.

Lens size has essentially nothing to do with magnification. You can get very high magnification with tiny lenses. Look at the size of the lens on a microscope.

Magnification is determined by the ratio of the image size to the size of the original. That will turn out to depend on the focal lengths of the lenses in use and on their exact arrangement. It will not depend upon their size.

If your resolution is diffraction-limited then using a larger lens (i.e. larger aperture) can improve matters. If your resolution is intensity-limited then using a larger lens (i.e. larger aperture) can improve matters. If your only problem is that the image is too small or too far away to make out clearly then magnification is a remedy. Magnifying an image reduces its intensity. This can put you into an intensity-limited situation. Hence the motivation for bigger lenses.

 

[cube137]

http://imageshack.com/a/img921/9752/kqlfcp.jpg

In the above. Binocular magnification increases the area 7X but the brightness stays the same. Does it mean the central portion retina still have the same photon density per unit area or more photon density per unit area? Is the effect of the larger apparent field of view more blue light entering the peripheral retina or can it affect even the central retina creating more photon density?

 

[sophiecentaur]

http://imageshack.com/a/img921/9752/kqlfcp.jpg

In the above. Binocular magnification increases the area 7X but the brightness stays the same. Does it mean the central portion retina still have the same photon density per unit area or more photon density per unit area? Is the effect of the larger apparent field of view more blue light entering the peripheral retina or can it affect even the central retina creating more photon density?

Apart from the possibility of some Flare, how / why would any more light fall on the centre of the retina? The optics of the eye are fairly good.

 

[cube137]

Apart from the possibility of some Flare, how / why would any more light fall on the centre of the retina? The optics of the eye are fairly good.

So the effect of telescope magnification

The basic idea to take away is that for an extended object the brightness of the object decreases with magnification. In this specific example, the increase in light-gathering ability of the binoculars over the eye is directly countered by the reduction in brightness by the increased magnification.
They can behave like extended objects, like point sources, or somewhere between, depending on the details.
The sunlight isn't spread to a larger area, it's spread to a smaller area. A magnifying glass is not a compound optical system and doesn't behave exactly like we've discussed here.

here's the mystery..

i removed the objective lens from my binocular and point it at sun focusing on the ground. you can see the central focus is much much brighter than the sunshine on the ground. isn't it that binocular or telescope just magnify the image to become larger with SAME brightness.. so how come the focus in the ground is much much brighter?

 

[davenn]

So the effect of telescope magnificationhere's the mystery..

i removed the objective lens from my binocular and point it at sun focusing on the ground. you can see the central focus is much much brighter than the sunshine on the ground. isn't it that binocular or telescope just magnify the image to become larger with SAME brightness.. so how come the focus in the ground is much much brighter?

You haven't listened to a thing people in this thread, including me, have told you over and over, have you ?? !

ONE LAST TIME

The light is being focussed into a smaller areaDave

 

[berkeman]

Thread closed for Moderation...

 

[berkeman]

Thread re-opened. Let's try to stay focused on the science here, folks. Oops, sorry for the pun...

 

[Drakkith]

here's the mystery..

i removed the objective lens from my binocular and point it at sun focusing on the ground. you can see the central focus is much much brighter than the sunshine on the ground. isn't it that binocular or telescope just magnify the image to become larger with SAME brightness.. so how come the focus in the ground is much much brighter?

Because the single lens acts as a simple magnifying glass. Without the eyepiece the objective lens can't be used to magnify far-away objects. Any telescope or binoculars needs both the objective and the eyepiece to function correctly.

I wish I had time to find some good pictures and to go into detail on this subject, but I'm doing homework and studying for a physics exam tomorrow.

 

[russ_watters]

here's the mystery..

i removed the objective lens from my binocular and point it at sun focusing on the ground. you can see the central focus is much much brighter than the sunshine on the ground. isn't it that binocular or telescope just magnify the image to become larger with SAME brightness.. so how come the focus in the ground is much much brighter?

There is no mystery here. "Bigger" and "brighter" are two separate things. Binoculars often make things both bigger and brighter. Bigger because of the magnification, brighter because of the size of the lens.

 

[cube137]

Because the single lens acts as a simple magnifying glass. Without the eyepiece the objective lens can't be used to magnify far-away objects. Any telescope or binoculars needs both the objective and the eyepiece to function correctly.

Yes. When I put an eyepiece between the objective lens the ground, the brightness at center is gone.. but it still is not same brightness as the sunshine. A telescope with eyepiece is supposed to make the brightness of target object and the magnified view same brightness. For those who think that a telescope focus all light to a point.. it's not entirely accurate.. the objective lens alone can act like magnifying glass.. But when you put eyepiece.. it redistributes the light to the magnified image. Anyway I still can't understand why the sunshine on the ground is not same brightness as the objective lens plus eyepiece.. you can't reason the telescope focus the light to smaller area (because the eyepiece redistributes) the light. I'm thinking hard and reviewing the thread over and over davenn..

I wish I had time to find some good pictures and to go into detail on this subject, but I'm doing homework and studying for a physics exam tomorrow.

physics exam? I thought physicsforums Mentors are former retired Nobel Laureates.

 

[russ_watters]

A telescope with eyepiece is supposed to make the brightness of target object and the magnified view same brightness.

That isn't true. As I said before, the two issues are not that closely related. This should be obvious given that you can use different eyepieces in the same telescope, which will produce different magnifications and brightnesses.

See the telescopes in my avatar? I can use different eyepieces on them to obtain the same magnification:
3000/40 = 75x
600/8 = 75x (actually, the smallest I have is a 9mm, but close enough...I also have Barlows and focal reducers)

But when viewing the moon through the big telescope, I need to use a filter to block most of the light, otherwise it hurts my eyes. Why? Because it pulls in a lot more light.

you can't reason the telescope focus the light to smaller area (because the eyepiece redistributes) the light.

Which is bigger: the lens or the spot on the ground the lens focuses the light to?

 

[Drakkith]

A telescope with eyepiece is supposed to make the brightness of target object and the magnified view same brightness.

Nope. Only a single magnification for each objective will do this. Changing out the eyepiece in a telescope for one of a different power will alter the brightness of the image.

Anyway I still can't understand why the sunshine on the ground is not same brightness as the objective lens plus eyepiece.. you can't reason the telescope focus the light to smaller area (because the eyepiece redistributes) the light.

See the following image:

Light, in this case from the center of the telescope's field of view, is focused down to a spot by the objective. Since there is nothing at the focal plane, the light continues on, diverging some before the eyepiece catches the diverging light and turns the rays parallel again. These parallel rays then enter your eye. Now, if you take away the eyepiece and place the objective such that the focal plane lies on the ground, the incoming light is focused down to a spot on the ground. So all that light that would be spread out is instead concentrated at a single spot.

physics exam? I thought physicsforums Mentors are former retired Nobel Laureates.

Someone must have forgotten to give me my check then.

 

[cube137]

That isn't true. As I said before, the two issues are not that closely related. This should be obvious given that you can use different eyepieces in the same telescope, which will produce different magnifications and brightnesses.

About 10 years ago. I bought a lot of astronomical equipments.. but didn't find a dark sky to use them so just put it in closet. I also bought a book Telescope Optics.. so I'm very familiar with basic stuff like Airy discs, exit pupils, etc. I just couldn't find the book now and kinda reviewing because of my new binocular hobby. By the way.. the refractor I bought is called APM 4" Apo.. I bought a special collector item with strehl ratio of 0.989 (equal to maybe 1/10 wavefront error). Do you think it's really good. The following is the spec.

See the telescopes in my avatar? I can use different eyepieces on them to obtain the same magnification:
3000/40 = 75x
600/8 = 75x (actually, the smallest I have is a 9mm, but close enough...I also have Barlows and focal reducers)

But when viewing the moon through the big telescope, I need to use a filter to block most of the light, otherwise it hurts my eyes. Why? Because it pulls in a lot more light.

Which is bigger: the lens or the spot on the ground the lens focuses the light to?

I know exil pupil is the determining factor of brightness. So viewing the moon through your big telescope. If the exit pupil is 7mm.. and you watch it with a smaller aperture and same exit pupil but lower magnification, the brightness is the same right??

I'm applying all it to terrestrial daytime view of my new binocular (I know exit pupil becomes 2.5mm). Looking at the sunshine at ground and fully intact binocular with sunshine shining thru it.. the spot on the ground even with eyepiece is still brighter than the sunshine... I guess the reasoning is like the brightness of the sun when viewed is not the same brightness of the sunshine on the ground.. isn't it.. the sun being brighter than the sunshine on ground.. using an intact binocular with eyepiece, you are magnifying the image of the sun.. and this is brighter than sunshine on ground.. what is the physics explanation of it.. that the sunshine on ground is less brighter than the sun when viewed directly.. by the way.. I know looking at sun naked eye or binocular/telescope can cause instant blindness so it's just theoretical.

 

[Drakkith]

I'm applying all it to terrestrial daytime view of my new binocular (I know exit pupil becomes 2.5mm).

A pair of 50x7 binoculars has an exit pupil of 7.14 mm, not 2.5 mm.

 

[cube137]

A pair of 50x7 binoculars has an exit pupil of 7.14 mm, not 2.5 mm.

Our eyes at daytime has pupil size of 2.5mm.. therefore the effective size of the 7x50 binocular becomes 2.5x7 = 17.5mm.. meaning you are only using 17.5mm of the 50mm objective.. it's like the resolution of 17.5mm objective lens.. you know.. stopping down aperture can lower resolution. etc

 

[Drakkith]

But you're not talking about the exit pupil of the binoculars, you're talking about the entrance pupil of the eye. A very important difference.

 

[cube137]

But you're not talking about the exit pupil of the binoculars, you're talking about the entrance pupil of the eye. A very important difference.

I know the distinction.. but since our pupil doesn't open more than 3mm at daytime.. I automatically assume the 7x50m 7.1mm exit pupil won't be utilized but only less than 3mm. This is why the worlds' best daytime binocular is size 8x30W. http://www.greatestbinoculars.com/a...vski/swarohabicht8x30w/swarohabicht8x30w.html I bought it for $1000. Now with all the data I learned in this thread. I know I have to avoid reflections from sunshine and at least know that viewing trees and leaves won't be dangerious even with more blue light because they won't be concentrated at the macula.. I was concerned before the light intensity would be increased at macula.. but reading that the brightness of the view is the same as the naked eye and only magnification increased (this is the reason for this thread).. then I'm relieved to know it is not harmful. Thanks to all who responded. I guess I'll move on now from theoretically optical physics to just enjoy the views.

 

[sophiecentaur]

There is no mystery here. "Bigger" and "brighter" are two separate things. Binoculars often make things both bigger and brighter. Bigger because of the magnification, brighter because of the size of the lens.

We have all told him as much but he can't / won't take it on board. I have given up.

 

[cube137]

We have all told him as much but he can't / won't take it on board. I have given up.

I already understood it. I'm now moving on from comprehending optical principles to just enjoy the view. Thanks a lot.