Binoculars and light amplification

[cube137]

http://www.rocketmime.com/astronomy/Telescope/Magnification.html

im studying from above how image is magnified in a binocular or telescope.
In binocular say 7X. can you say light is amplified or jus magnified? if amplified, is it 7 times? if just magnified and not amplified. how come using binocular on the sun can blind person faster than naked eye?

also for example you are viewing buildings at daytime and suddenly you see the sun reflected from the building glasses... is the effect like looking at the sun directly.. or how much reduction if not same exposure?

 

[mgkii]

Hi @cube137 It's definitely magnified. If you think back to the way you can burn things with a magnifying glass, you're taking all of the solar energy that would normally hit the ground over the area of the magnifying glass, and focusing it into a tiny area. Same goes for looking at the sun through a telescope; if you stare at the sun unaided with just the area of your pupil letting in light you'll go blind. Pump in rays from the area of the telescope lens through your pupil and you'll go blind more quickly!

I think (open to challenge) if you want amplification, you would need to be adding additional light from another source - think of the analogy of how a guitar amp works; takes in a small voltage and amplifies it to a larger one, but you feed it additional voltage from an external source.

Regarding your question on reflected light then there's a number of factors in play. If you ignore any loss through the reflected surface, from the lenses themselves, etc then there's no difference to looking at the sun direct - just like shining a torch in your eyes directly or into a mirror first. However, the other factors will undoubtedly have a reducing effect - not all light may get reflected; the lenses may have coatings which reduces throughput, etc.

 

[cube137]

Hi @cube137 It's definitely magnified. If you think back to the way you can burn things with a magnifying glass, you're taking all of the solar energy that would normally hit the ground over the area of the magnifying glass, and focusing it into a tiny area. Same goes for looking at the sun through a telescope; if you stare at the sun unaided with just the area of your pupil letting in light you'll go blind. Pump in rays from the area of the telescope lens through your pupil and you'll go blind more quickly!

I think (open to challenge) if you want amplification, you would need to be adding additional light from another source - think of the analogy of how a guitar amp works; takes in a small voltage and amplifies it to a larger one, but you feed it additional voltage from an external source.

Regarding your question on reflected light then there's a number of factors in play. If you ignore any loss through the reflected surface, from the lenses themselves, etc then there's no difference to looking at the sun direct - just like shining a torch in your eyes directly or into a mirror first. However, the other factors will undoubtedly have a reducing effect - not all light may get reflected; the lenses may have coatings which reduces throughput, etc.

thanks for sharing.. but isn't magnify and amplify same meaning?

 

[mgkii]

Pretty sure the answer is no. Any use of the word magnify I can think of involves looking at the same "stuff" more closely, or in the case of lenses taking the same amount of light and concentrating it into a smaller area. By contrast, I can't think of any use of the work Amplify that doesn't involve adding more "stuff" to the original - e.g. amplify sound = plug in a powered amplifier; or amplify light you need to add more light

There's plenty of references out there to the difference between magnify and amplify - here's a couple of examples :
1. Magnification is increasing the size of something; amplification is increasing the contrast of something. If you were to amplify an image, the contrast between lights and darks would be increased, allowing subtle details to be seen. To magnify it would instead make it larger, allowing smaller details to be seen. Amplifying a sound makes it louder because it increases the contrast between the highs and lows of the waves.

2. Magnify is to make something look bigger . Amplify is to make the amount (volume) bigger.

 

[cube137]

Pretty sure the answer is no. Any use of the word magnify I can think of involves looking at the same "stuff" more closely, or in the case of lenses taking the same amount of light and concentrating it into a smaller area. By contrast, I can't think of any use of the work Amplify that doesn't involve adding more "stuff" to the original - e.g. amplify sound = plug in a powered amplifier; or amplify light you need to add more light

There's plenty of references out there to the difference between magnify and amplify - here's a couple of examples :
1. Magnification is increasing the size of something; amplification is increasing the contrast of something. If you were to amplify an image, the contrast between lights and darks would be increased, allowing subtle details to be seen. To magnify it would instead make it larger, allowing smaller details to be seen. Amplifying a sound makes it louder because it increases the contrast between the highs and lows of the waves.

2. Magnify is to make something look bigger . Amplify is to make the amount (volume) bigger.

are you familiar with magnification principles of binoculars or telescopes in the link i shared in the first image? if you do.. well in binocular or telescope.. do you consider the brightness as many times increased or same brightness as original view?

 

[sophiecentaur]

thanks for sharing.. but isn't magnify and amplify same meaning?

Both terms are in common use by non-technical people so you can't rely on what you read in many places. I think it's pretty sure to say that 'amplification' needs an 'amplifier', which uses a source signal (input light / sound/ etc) to control the power from another energy source and produce a more Powerful output signal.
So a simple lever can only be a Force Magnifier because the energy got out, by raising a weight, say, can only be less than the energy put in. But a servo system can be a Force Amplifier because it uses electrical (or other) power to do the work.
I would beware using Dictionary and Encyclopaedia entries as arbiters of such things and rely more on a number of 'learned' articles. The more you know about a topic, the more errors you find in 'journalistic' sources. (Same goes for News Reporting)

 

[mgkii]

are you familiar with magnification principles of binoculars or telescopes in the link i shared in the first image? if you do.. well in binocular or telescope.. do you consider the brightness as many times increased or same brightness as original view?

I am familiar with the principle. The brightness is increased - think back to the magnifying glass burning something. However, I still maintain that this is magnification and not amplification as you're not adding anything new into the mix, just focussing what's already there to start with.

 

[sophiecentaur]

in binocular or telescope.. do you consider the brightness as many times increased or same brightness as original view?

The 50mm (say) telescope gathers much more light energy than your 2mm (say) pupil so this can produce a brighter image than with the naked eye without using an 'amplifier'.

 

[cube137]

I am familiar with the principle. The brightness is increased - think back to the magnifying glass burning something. However, I still maintain that this is magnification and not amplification as you're not adding anything new into the mix, just focussing what's already there to start with.

for a binocular of 50mm objective size and 7 X magnification.. how many times is the brightness increased? 7 times too.. what ? how do you compute for it? thanks

 

[cube137]

I was asking all this because what if you were viewing the green leaves with very strong sunlight at 8X. I heard blue light can cause macular degeneration. If you use naked eye. Let's say you only view the scenery with many shadows and some with sunlight.. but say only 7 degrees of the field of view has strong sunlight.. now when you aim your 8X binocular with 7 degrees field of view.. you would see entirely the green leaves with strong sunlight.. won't this produce strong blue light that can harm the eyes (versus viewing with the eyes only where majority of the scene are dark or without sunlight). I know the arguments that if the naked eye scene and binocular scene are equally bright.. the binocular glassses may even attenuate the blue light making one with binocular safer... but I'm talking of the bright sunlight on the leaves at only 7 degree field of view.. this would produce 7x8=56 degree apparent field where the entirely is leaves with strong sunlight and more blue light.

 

[sophiecentaur]

Remember, there are two things at work; magnification and aperture (objective diameter, in this case). A wide objective lens will gather more light and can reduce diffraction effects ( which may or may not be relevant, depending on other aberrations. Light power reaching the eye will be proportional to lens area but, afaik, will also be proportional to the field and the two can cancel each other out.
I know nothing of how blue light can affect macular degen; does it depend only on incident energy density or total input to the eye?

 

[cube137]

Remember, there are two things at work; magnification and aperture (objective diameter, in this case). A wide objective lens will gather more light and can reduce diffraction effects ( which may or may not be relevant, depending on other aberrations. Light power reaching the eye will be proportional to lens area but, afaik, will also be proportional to the field and the two can cancel each other out.
I know nothing of how blue light can affect macular degen; does it depend only on incident energy density or total input to the eye?

http://www.reviewofoptometry.com/continuing_education/tabviewtest/lessonid/109744/
https://www.macular.org/ultra-violet-and-blue-light

What do you mean by "Light power reaching the eye will be proportional to lens area but, afaik, will also be proportional to the field and the two can cancel each other out."? I'm familiar with the basic of how telescope magnification work.. but rephrase it.. thanks.

 

[davenn]

What do you mean by "Light power reaching the eye will be proportional to lens area

the larger the lens or mirror the more light that is gathered

but, afaik, will also be proportional to the field and the two can cancel each other out."?

what field ??

I'm familiar with the basic of how telescope magnification work..

that statement is in contradiction to everything else you have posted in the thread so far

your complete answer was given to you in post #2 and backed up in post #4
Dave

 

[lychette]

thanks for sharing.. but isn't magnify and amplify same meaning?

Magnify and amplify are words in common usage. When they are used in physics they are usually defined in a specific way.
In optics magnification means size of object/size of image (standard textbook definition)so there is no confusion with amplification or any other term.
Note...'size' may be linear or angular. So magnification of X7 could mean that the image is 7 times longer than the object or that the angle subtended at the eye by the image is 7X the angle subtended at the eye by the object.

 

[cube137]

but, afaik, will also be proportional to the field and the two can cancel each other out."?
what field ??

that quotation about "field" came from sophiecentaur.. I was asking her (or him?) what he meant by it when she said "but, afaik, will also be proportional to the field and the two can cancel each other out".. well sophie?

 

[cube137]

I asked all this because I'd like to know the following regard blue light magnification.

Supposed you are in a forest in a shade in overcast sky.. and you saw a tree with sunshine shining on it and you aim your 8X binocular into it.. in your eyepiece, the entire leaves in the tree would be exposed to sunshine.. would this transmit more blue light to your eyes than when you don't use the binocular and the sunshine in the leaves is just 7 degrees in your field of vision with the rest without sunshine?

 

[sophiecentaur]

I as referring to field of view - i.e. how many degrees wide. Sloppy of me, without a definition. Sorry. I did think that Field was a well known term, aamof.
I'm a him with a PF profile. The name is historical and too late to change, I think.
My point was that the field will define the portion of the scene that's admitted to the sensor array / film / retina. That tells you how much of the energy source is available. The area of the objective governs how much of the energy from each point on the source its gathered. I think that means that doubling the magnification (linear) will reduce the useful energy admitted to the sensor, which requires doubling of the objective diameter in order to obtain the same brightness of image. I think that's the right argument.

 

[davenn]

that quotation about "field" came from sophiecentaur.. I was asking her (or him?) what he meant by it when she said "but, afaik, will also be proportional to the field and the two can cancel each other out".. well sophie?

ahhh ok, not sure what he is getting at there either ??

in your eyepiece, the entire leaves in the tree would be exposed to sunshine.. would this transmit more blue light to your eyes than when you don't use the binocular and the sunshine in the leaves is just 7 degrees in your field of vision with the rest without sunshine?

well considering that is the leaves are green, as is common ( I haven't seen many blue leaved trees ), there is going to be little or no blue light coming off themDave

 

[sophiecentaur]

I think a more 'ideal' scenario than 'the leaves' would be better to discuss this problem with. A black screen with a white patch in the middle would be more appropriate, I reckon. We could discuss colours later on.

 

[Merlin3189]

You've got it right with the 7 x 50 binoculars. The image is magnified 10x, it looks 10x as big. The diameter of the objective lens is 50mm and its area is about 2000mm² which is bigger than the pupil of your eye (at up to about 50mm²) So it allows through at least 40x more light than your unaided pupil would and therefore has more light available to make a brighter image.
The magnification works against this concentration of light, since as the image is made bigger, the light is spread over a larger area. If the image is 10x larger, then its area is 100x greater. So with the numbers above, you actually get a dimmer image with the binoculars 40% as bright as with your unaided eye. However I took a maximum value for your pupil and a more realistic area for your pupil area might be 5mm diameter, about 20 mm², meaning the 50 mm diameter binocular objective would collect about 100x more light than your pupil and, after allowing for magnification, the image would have the same brightness.
There is yet another link in the chain known as the exit pupil of the telescope, which represents the area of pupil needed to accept all the light leaving it. This exit pupil is calculated by dividing the objective diameter by the magnification, so the 7 x 50 binoculars have an exit pupil of about 7mm. All the light from the binocular will enter your eye only if your pupil is at least 7mm diameter, otherwise some will be blocked.
After all that the small amounts lost by reflections at lens (and prism) surfaces probably don't make much difference to the image brightness, though they may affect the quality by lowering contrast and maybe producing spurious image effects.

Now I'm no expert on this and had to do a lot of checking before replying. I find the conclusions difficult to swallow, because I feel I do see things more brightly through my 10x50 binoculars or my 70x112 telescope even though their calculated brightnesses are only around 100%.
I wonder whether this is a property of the retina & brain, whereby 100x as much light spread over 100x the area is more detectable, even though physically it is the same brightness? (That is my speculation.)
Or maybe because we are talking about point sources (at least, I am, talking about stars) magnification of a point does not produce a bigger point: the light entering my unaided eye gets spread over an Airy disc and the light from the telescope is still imaged on my retina to a similarly sized Airy disc - only the spaces between the stars being magnified? (Also speculation. Only just thought of that one!)

Edit. PS I'm sure we have astronomers on PF. I hope one of them will shed a bit of light on this.

 

[sophiecentaur]

Try the astronomy forum. People don't always stray out of their favourite playgrounds.

 

[cube137]

You've got it right with the 7 x 50 binoculars. The image is magnified 10x, it looks 10x as big. The diameter of the objective lens is 50mm and its area is about 2000mm² which is bigger than the pupil of your eye (at up to about 50mm²) So it allows through at least 40x more light than your unaided pupil would and therefore has more light available to make a brighter image.
The magnification works against this concentration of light, since as the image is made bigger, the light is spread over a larger area. If the image is 10x larger, then its area is 100x greater. So with the numbers above, you actually get a dimmer image with the binoculars 40% as bright as with your unaided eye. However I took a maximum value for your pupil and a more realistic area for your pupil area might be 5mm diameter, about 20 mm², meaning the 50 mm diameter binocular objective would collect about 100x more light than your pupil and, after allowing for magnification, the image would have the same brightness.
There is yet another link in the chain known as the exit pupil of the telescope, which represents the area of pupil needed to accept all the light leaving it. This exit pupil is calculated by dividing the objective diameter by the magnification, so the 7 x 50 binoculars have an exit pupil of about 7mm. All the light from the binocular will enter your eye only if your pupil is at least 7mm diameter, otherwise some will be blocked.
After all that the small amounts lost by reflections at lens (and prism) surfaces probably don't make much difference to the image brightness, though they may affect the quality by lowering contrast and maybe producing spurious image effects.

Now I'm no expert on this and had to do a lot of checking before replying. I find the conclusions difficult to swallow, because I feel I do see things more brightly through my 10x50 binoculars or my 70x112 telescope even though their calculated brightnesses are only around 100%.
I wonder whether this is a property of the retina & brain, whereby 100x as much light spread over 100x the area is more detectable, even though physically it is the same brightness? (That is my speculation.)
Or maybe because we are talking about point sources (at least, I am, talking about stars) magnification of a point does not produce a bigger point: the light entering my unaided eye gets spread over an Airy disc and the light from the telescope is still imaged on my retina to a similarly sized Airy disc - only the spaces between the stars being magnified? (Also speculation. Only just thought of that one!)

Edit. PS I'm sure we have astronomers on PF. I hope one of them will shed a bit of light on this.

My question is this. Since the objective lens collect 40 times more light and focus this to a point. Why doesn't our retina detect this single point as 40 times brighter.. or does it? Because it seems our eyes detect the brightness as the same as the original view. But there is 40 times more brightness. Note I'm talking of a single angle.. so you can't reason as magnification got bigger it spreads to larger area.. this is for total of all angles.. I'm talking of just one angle.. one ray and one focus that is 40 times brighter and hitting one retina...

 

[Merlin3189]

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

 

[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

Ok. Supposed there was a black screen with a white patch in the middle which sophie suggest to use as initial example. Or supposed let's use the example of black screen with a source of blue light at the center that span 7 degrees. Using the 8X binocular, the eyepiece (apparent) field of view would be 7x8=56 degrees. So this means the blue light is indeed magnified to your eyes (meaning your retina receive more blue light overall) using the binocular versus just staring at the background using naked eye?

 

[sophiecentaur]

Since the objective lens collect 40 times more light and focus this to a point.

But, as Merlin has been saying (and me, also) there is no such thing as a single point when you are dealing with power flow. An object consists of infinitesimal elements, each of which produces an infinitesimal amount of energy - that is an energy flux density. In the case of astronomy, all the star images are the size of the diffraction pattern and they are still not absolute points, as far as the energy coming out of your binos or into your eye. A cm² or a 1° subtended diameter of image will send light in a cone that fills your pupil and produce a given signal level from each of a number of retinal cells over an area of your retina. Your binos have a larger objective lens and will collect more light but that light is spread over a bigger area of retina (a magnified image). If all the light entering the objective got into your pupil then the increase in brightness would be in the ratio of the areas of lens and pupil (but, as Merlin says) it doesn't all get there. IF it did, you would find only one viewing position where you could actually see anything. So you have some proportion of all the gathered light entering your pupil (making things brighter) but it forms a bigger image so the energy flux density is lower so it won't be as much brighter than you might have assumed.
I guess the design of binos and spotting telescopes gives a is based on the fact that most scenes are bright enough to allow you to see things and the exit aperture is made big enough for comfortable viewing. That could account for Merlin's experience with his equipment. I would imagine that telescope systems designed for photographing faint astronomical objects may be arranged differently, to get the image as bright as possible at the expense of needing to get the camera alligned more precisely (? Could that be right, Merlin?)

 

[cube137]

But, as Merlin has been saying (and me, also) there is no such thing as a single point when you are dealing with power flow. An object consists of infinitesimal elements, each of which produces an infinitesimal amount of energy - that is an energy flux density. In the case of astronomy, all the star images are the size of the diffraction pattern and they are still not absolute points, as far as the energy coming out of your binos or into your eye. A cm² or a 1° subtended diameter of image will send light in a cone that fills your pupil and produce a given signal level from each of a number of retinal cells over an area of your retina. Your binos have a larger objective lens and will collect more light but that light is spread over a bigger area of retina (a magnified image). If all the light entering the objective got into your pupil then the increase in brightness would be in the ratio of the areas of lens and pupil (but, as Merlin says) it doesn't all get there. IF it did, you would find only one viewing position where you could actually see anything. So you have some proportion of all the gathered light entering your pupil (making things brighter) but it forms a bigger image so the energy flux density is lower so it won't be as much brighter than you might have assumed.
I guess the design of binos and spotting telescopes gives a is based on the fact that most scenes are bright enough to allow you to see things and the exit aperture is made big enough for comfortable viewing. That could account for Merlin's experience with his equipment. I would imagine that telescope systems designed for photographing faint astronomical objects may be arranged differently, to get the image as bright as possible at the expense of needing to get the camera alligned more precisely (? Could that be right, Merlin?)

Ok. 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 (which as you say makes the image not so bright or not proportional to area of objective lens and eye pupil) but all the angles seen by the objective lens is focus to one single point.. would this turn it into a laser? how does one do this... or theoretically.. how must the light collector (formerly objective lens) have to be designed?

 

[davenn]

Ok. 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 (which as you say makes the image not so bright or not proportional to area of objective lens and eye pupil) but all the angles seen by the objective lens is focus to one single point.. would this turn it into a laser? how does one do this... or theoretically.. how must the light collector (formerly objective lens) have to be designed?

you really need to go do some reading on telescope and other optical instrument systems
Again, despite your earlier comment of knowing about how they work, it's very obvious you don't understand the basics, else you wouldn't be asking these same questions over and over

do some google searching on optical ray paths for lenses and telescopes

here's a starting point with images showing ray paths etc I will let you
start doing some further research yourself

http://www.bing.com/images/search?q=ray+paths+for+telescopes&FORM=HDRSC2

would this turn it into a laser? how does one do this...

no it doesn't ... a laser is a different ball game

a laser is a coherent light source, light from stars, the sun and other objects is non-coherent

https://en.wikipedia.org/wiki/Laser

Dave

 

[cube137]

you really need to go do some reading on telescope and other optical instrument systems
Again, despite your earlier comment of knowing about how they work, it's very obvious you don't understand the basics, else you wouldn't be asking these same questions over and over

do some google searching on optical ray paths for lenses and telescopes

here's a starting point with images showing ray paths etc I will let you
start doing some further research yourself

http://www.bing.com/images/search?q=ray+paths+for+telescopes&FORM=HDRSC2Dave

I understood it that eyepiece shows greater angle in the object subtended so greater magnification. My question above is because I understand how telescope works already from the inputs of guys here. So I'm asking what kind of optical system can you make all the available light in the scene focus into one single point.. this can produce a laser.. is there weapon like this where you use all the available photons in the scene and focus on a point (I know not how telescope work)

 

[davenn]

So I'm asking what kind of optical system can you make all the available light in the scene focus into one single point..

again, that has already been answered ( a single lens)... a magnifying glass will do that

the available light in the scene focus into one single point.. this can produce a laser.. is there weapon like this where you use all the available photons in the scene and focus on a point (I know not how telescope work

again, no it can't ... read the last section of my previous postDave

 

[cube137]

again, that has already been answered ( a single lens)... a magnifying glass will do that

As I already understand.. all the available light being focused to a point is only from one very small angle... different angles would have different points of focus. My question is a special design optical system in which all angles from distance is focused to same point.. this would produce a laser. Anyway since you said this can't be designed. Then ok.

 

[davenn]

My question is a special design optical system in which all angles from distance is focused to same point.. this would produce a laser. Anyway since you said this can't be designed. Then ok.

read the wiki link on lasers that I gave you several posts ago

 

[davenn]

All optical systems that magnify the object being viewed are inherently narrow field of view systems
telescope, binoculars, microscope, camera
The higher the magnification, the smaller the field of view, one is proportional to the other

The wider the angle of view, say a wide angle fish eye lens system for a camera will have a very short focal length, less than 20mm
and could have a field of view easily up to 180 degrees. The front of the lens will be highly curved...

Dave

 

[cube137]

Ok. I understand the basic already. To wrap up on my blue light question. Supposed there was a black screen with a white patch in the middle which sophie suggest to use as initial example. Or supposed let's use the example of black screen with a source of blue light at the center that span 7 degrees. Using the 8X binocular, the eyepiece (apparent) field of view would be 7x8=56 degrees. So this means the blue light is indeed magnified to your eyes (meaning your retina receive more blue light overall) using the binocular versus just staring at the background using naked eye? Yes or No. Thanks.

 

[davenn]

Or supposed let's use the example of black screen with a source of blue light at the center that span 7 degrees. Using the 8X binocular, the eyepiece (apparent) field of view would be 7x8=56 degrees. So this means the blue light is indeed magnified to your eyes (meaning your retina receive more blue light overall) using the binocular versus just staring at the background using naked eye? Yes or No. Thanks.

did you read my post #18 ?
same answer for this latest Q from you ...
do you understand why the screen looks black ( or whatever colour you make it) ?
consider again why a green leaf looks green ... ALL colours except green are going to be absorbed
can you then understand why you are going to see somewhere between a tiny amount and no blue light at all ?

Dave

 

[cube137]

did you read my post #18 ?
same answer for this latest Q from you ...
do you understand why the screen looks black ( or whatever colour you make it) ?
consider again why a green leaf looks green ... ALL colours except green are going to be absorbed
can you then understand why you are going to see somewhere between a tiny amount and no blue light at all ?

Dave

Ok. Let's replace the green leafs with the blue of the sky or better yet.. let's make the target view as a compact fluorescent lamp.

http://www.reviewofoptometry.com/continuing_education/tabviewtest/lessonid/109744/

"Nowadays, there's an increase in the use of digital devices and modern lighting—such as LED lights and compact fluorescent lamps (CFLs)—most of which emit a high level of blue light. CFLs contain about 25% of harmful blue light and LEDs contain about 35% of harmful blue light. Interestingly, the cooler the white LED, the higher the blue proportion. And by 2020, 90% of all of our light sources are estimated to be LED lighting. So, our exposure to blue light is everywhere and only increasing."

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? .

 

[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.