Brightest Images

[syed]

FRIENDS,
I have learnt a thing while searching for information about binoculars which quite puts off the passion for them.
VIEWING WITH BINOCULARS OR SCOPES CAN NOT BE BRIGHTER THAN VIEWING WITH NAKED EYES NO MATTER WHATEVER BE THE APERTURE.

IMAGES ARE THE BRIGHTEST WHEN VIEWED WITH NAKED EYES.
This fact really makes me disappointed.
Is it true?
if it is then why so much hype about light gathering power of binoculars and scopes.They can't be brighter than your eyes!!

ANY REPLIES??B (:B (:

[John P]

My eyes haven't quite mastered the X8.5 magnification yet, so I'll stick with my bins thanks.;)

[etudiant]

It may be that the benefits of the light gathered by the objective lenses is not easily perceived in daytime. Dusk is a better time to appreciate the extra brightness binoculars bring. Birds lost in the dark jump into life through binoculars.

[Kevin Conville]

My eyes haven't quite mastered the X8.5 magnification yet, so I'll stick with my bins thanks.;)

Thanks John, that made me smile. |;|

[Surveyor]

Hello syed;

These are just my thoughts and someone more knowledgeable may be able to confirm or correct this.

While technically correct that the luminous flux entering the objective will be reduced by transmission losses (lumens) the field intensity will be greater, same lumens in less area (entrance pupil/exit pupil ratio or power) yields higher lux values. Take the moon for instance, looking at it with the naked eye is a comfortable view but looking through a higher-powered optic can be downright uncomfortable. The intensity applied on a small angular portion of the retina as compared to 90% of the power applied to a very large angle covering the whole retina. Magnification changes the perceived brightness, for example you may measure a light source to be 200 lux at the objective and measure 1000 lux in the exit pupil.

Ron

[Kevin Conville]

Sounds right to me Ron.

Syed-
What is your point anyway? You still need magnification, right?
You obviously cannot see as well with the naked eye so does some abstract bit of knowledge from a white paper mean you'll quit using binoculars?

I, and countless others, can cite anecdote after anecdote that conflicts or contradicts your statement. I prove it to myself almost every evening.
Look up twilight factor and see if any of that makes sense to you.

"why so much hype about light gathering power of binoculars and scopes.They can't be brighter than your eyes!!"
If one can gather more light with the naked eye compared to binoculars still has nothing to do with a 50mm binocular gathering more light than a 32mm bino. They are mutually exclusive concepts.

Use your binos, enjoy them, and see more!

[syed]

NOT RIGHT SURVEYOR!!
In fact the brightness perceived is lesser in binoculars than perceived by the eye .
I have read somewhere that this is due to second law of thermodynamics(don't know why?)
As you increase the aperture in order to have a brighter image you need also to increase magnification to limit the size of exit pupil and the increased magnification decreases the image bightness by an equal amount.
So you end up where you began.
FAINTER THAN THE NAKED EYE.
ARE LARGE APERTURES REALLY SO UNIMPORTANT?
(7 mm eye beating 150 mm binocular in brightness!!)B (:B (:

[Surveyor]

NOT RIGHT SURVEYOR!!

FAINTER THAN THE NAKED EYE.
ARE LARGE APERTURES REALLY SO UNIMPORTANT?
(7 mm eye beating 150 mm binocular in brightness!!)B (:B (:

Hi syed;

Try a simple experiment. Find a bright light (100 watt bulb at 10') and look at it naked eye then with a binocular. DO NOT use the sun. ;)

Best
Ron

[ThoLa]

FRIENDS,
I have learnt a thing while searching for information about binoculars which quite puts off the passion for them.
VIEWING WITH BINOCULARS OR SCOPES CAN NOT BE BRIGHTER THAN VIEWING WITH NAKED EYES NO MATTER WHATEVER BE THE APERTURE.

IMAGES ARE THE BRIGHTEST WHEN VIEWED WITH NAKED EYES.
This fact really makes me disappointed.
Is it true?
if it is then why so much hype about light gathering power of binoculars and scopes.They can't be brighter than your eyes!!

ANY REPLIES??B (:B (:


Let's hope that professional astronomers will hear about this interesting new finding.
There will be lots of formerly very expensive professional equipment available for very low prices soon.
I#ll have a reservation for a 3m telescope (even if my eyes are brighter).
T

[lucznik]

FRIENDS,
I have learnt a thing while searching for information about binoculars which quite puts off the passion for them.
VIEWING WITH BINOCULARS OR SCOPES CAN NOT BE BRIGHTER THAN VIEWING WITH NAKED EYES NO MATTER WHATEVER BE THE APERTURE.

IMAGES ARE THE BRIGHTEST WHEN VIEWED WITH NAKED EYES.
This fact really makes me disappointed.
Is it true?
if it is then why so much hype about light gathering power of binoculars and scopes.They can't be brighter than your eyes!!

ANY REPLIES??B (:B (:

I'm not sure what exercise in logic would have brought you to a conclusion that by looking through a passive optical instrument like a binocular with all its glass and prisms you would somehow have more light hitting your eyes than is available to the naked eye but, it certainly was flawed logic. Binoculars magnify the view. They do not manufacture extra light.

I think your problem syed, is that you have misunderstood the point and purpose of binoculars to begin with. They do not exist to make things brighter but rather to allow you to view them in detail from farther away. A binocular allows you to see, study, and admire the subtle differences and colors of a bird's plumage, their behavioural characteristics, and other unique attributes from a distance that does not scare them away. Sure, you lose a couple percentage points in overall light loss but, you do get to enjoy the view closeup - which you would not be able to do with just your naked eyes.

[J. Moore]

I'm not sure what exercise in logic would have brought you to a conclusion that by looking through a passive optical instrument like a binocular with all its glass and prisms you would somehow have more light hitting your eyes than is available to the naked eye

In his original post he mentioned binocular hype, which does seem to suggest that binoculars gather "more" light.

Eagle Optics Leica page states that one of its binoculars is a "light gathering wonder", and says "Leica's optical glass works powerfully behind the scene to reduce stray light and generate increased light transmission and contrast."

http://www.eagleoptics.com/index.asp?pid=3818

While I do not not think such language is false, or actually states the binocular gathers more light than the human eye, it is arguably misleading in that respect.

And with respect to night vision binoculars, I assume you do not regard those as "passive"?

Best,
Jim

[lucznik]

Eagle Optics Leica page states that one of its binoculars is a "light gathering wonder", and says "Leica's optical glass works powerfully behind the scene to reduce stray light and generate increased light transmission and contrast."

http://www.eagleoptics.com/index.asp?pid=3818

While I do not not think such language is false, or actually states the binocular gathers more light than the human eye, it is arguably misleading in that respect. I definitely can see where a casual or uneducated reader could come to an erroneous conclusion here. This is the ever-present problem with advertising copy. I will point out that a more careful reading reveals that what Leica is saying is that it generates increased light transmission and contrast relative to their competitors' (and their own) current and/or previous offerings.

And with respect to night vision binoculars, I assume you do not regard those as "passive"?
Correct. I would regard night vision optics as "active" optical instruments. The fact that they require batteries to operate would be one way of telling the difference.

[Swedpat]

FRIENDS,
I have learnt a thing while searching for information about binoculars which quite puts off the passion for them.
VIEWING WITH BINOCULARS OR SCOPES CAN NOT BE BRIGHTER THAN VIEWING WITH NAKED EYES NO MATTER WHATEVER BE THE APERTURE.

IMAGES ARE THE BRIGHTEST WHEN VIEWED WITH NAKED EYES.
This fact really makes me disappointed.
Is it true?
if it is then why so much hype about light gathering power of binoculars and scopes.They can't be brighter than your eyes!!

ANY REPLIES??B (:B (:

Hi!

I know there are yet many answers, but I want contribute with some comments. If we are talking about RELATIVE brightness, which is the same as how bright an image appears (not the same as how dazzled you will be looking against a light source), the answer is no. But still it may be yes...

I want to explain: theoretically the relative brightness can never be higher than the exit pupil. And because of the light loss due to the reflections of the lens system (even if the light loss can be decreased with an antireflex coating) the brightest possible binocular will still be dimmer than the naked eye.

Despite that, we can during some circumstances experience a brighter image through a binocular. There are two reasons of this:

1: the much narrower apparant field of view in comparison to the naked eye.

2: The eye cups of the binocular can cover the face so the eyes will be protected from stray light.

Anyway, using a high quality glass with a high class coating, you will never experience the image to be dimmer than your naked eye as long the exit pupil is as least the same as your eye pupil.

Regards, Patric

[Robert / Seattle]

I think Syed was perhaps confused by the fact that the human eye has a reduced exit pupil in bright light, and that no matter how much light an optic delivers, it will not appear brighter than any alternative optic that also exceeds this daylight minimum. This is why, of course, there is no daytime functional difference in perceived light gathering between a 10x42 and a 10x32 binocular, for example - that is, until light levels drop and the relative light gathering of the two configurations become apparent. This is also why older folks, with inherently diminished exit pupils, derive little or no apparent benefit from a larger objective lens under most any condition.

This is perhaps better explained by Michael Porter here:
http://www.birdwatching.com/optics/light-to-the-eye.html --
which in summary is quoted below:

"You often hear that a larger exit pupil makes a binocular brighter. It's true, but only within limits. We can see only the light that enters through our pupils.

"In daylight, when the pupils are perhaps as small as 2 millimeters, part of the column of light coming through the binocular will fall on the iris (pigmented part) of the eye instead of the pupil. That part of the light does not contribute to the brightness of the image. ...

This is the reason that a binocular such as an 8x32, with an exit pupil of 4mm, usually gives just as bright an image as an 8x42 binocular of equal quality.

The older a person is, the less the pupil dilates in dark conditions. That's why compact binoculars, such as an 8x32, seem to be just made for an older person. For pupils that remain relatively small even in dim conditions, the smaller objective lens and smaller exit pupil provide just as bright an image as a larger, heavier, more expensive binocular."

[mooreorless]

If you are looking at an object at 100 meters with a true fully multicoated 10x70 mm or 80mm binocular in very low light , can you see as good as if you were standing 10 meters away looking dark adapted naked eyes in both instances?
Regards,Steve

[Robert / Seattle]

If you are looking at an object at 100 meters with a true fully multicoated 10x70 mm or 80mm binocular in very low light , can you see as good as if you were standing 10 meters away looking dark adapted naked eyes in both instances?
Regards,Steve

I think under those conditions, the binocular would trump the eye, i.e., deliver more light to the eye than it would otherwise gather.

[lucznik]

I think under those conditions, the binocular would trump the eye, i.e., deliver more light to the eye than it would otherwise gather.

It might appear brighter due to both the magnification of the image and the fact that the binocular causes a bit of a tunnel effect which makes things look brighter because everything around the periphery of the image is a black circle but, this is an optical illusion.

Every time light hits a glass surface in the light path through the binocular a small percentage of that light is reflected away and lost. This causes the final image hitting the retina to have less light than was available to the naked eye. This is a simple matter of physics and is not dependent on "conditions." The binocular might indeed still trump the naked eye and you may indeed be able to see things better through a binocular in low light than you can with the naked eye but, this is not due to an increase in light but rather to an increase in magnification.

[lucznik]

If you are looking at an object at 100 meters with a true fully multicoated 10x70 mm or 80mm binocular in very low light , can you see as good as if you were standing 10 meters away looking dark adapted naked eyes in both instances?
Regards,Steve

Actually, you might be able to see better because the tunnel effect common to all binoculars can serve to help you focus more keenly on the item of interest thanks to the fact that much of your peripheral vision is effectively blocked out. This has nothing to do with any increase in light. In fact, the image you are looking at through that fully-multicoated 10x70 or 80 binocular is always going to be darker than what was possible with the naked eye because, as already explained, every time the light passes through or is refracted by a prism as it travels the optical path of your binocular, a small percentage of that light is reflected away and lost.

Total light "transmission" really is only a part (though admittedly a large part) of overall image quality.

[lucznik]

** deleted as I think I discovered a fundamental error in my example. **

[syed]

Guys
The main point is that we are not talking about the "total amount of light".
We are talking about brightness which in the simplest terms is

(TOTAL AMOUNT OF LIGHT)/(AREA OF IMAGE)

The total amount of light gathered by a binocular or scope can be greater than the amount of light gathered by the eye .
BUT THAT DOESN'T MAKE A DIFFERENCE.
As soon as you divide it by image area you get the same brightness (in fact lesser than what your naked eye can see).
Leave magnification aside and you get nothing big out of a large aperture.

One more point is that if you view stars with the help of your binoculars than they are really brighter than naked eyes because stars are point sources as viewed from earth and hence there is no reduction in thier brightness as magnification is increased.
But if you talk about extended objects ( AND BIRDS CERTAINLY ARE EXTENDED OBJECTS ) the eyes are still the brightest because as a larger aperture increases the total amount of light yet the magnification produced by it increases the image area BY THE SAME AMOUNT and hence the brightness,which is a ratio of the two quantities , remains the same NO MATTER HOW MUCH LARGE YOUR OBJECTIVES ARE.
Doesn,t that indicate that BIG binoculars are a waste when the goal is to view faint objects or in faint conditions.
WHY SO MUCH MONEY FOR APERTURE.
So still lucznik
EYES ARE THE BRIGHTEST!!!B (:B (:

[lucznik]

So still lucznik
EYES ARE THE BRIGHTEST!!!B (:B (:
I believe that is what I have been saying. The view with the naked eye is always brighter than that of the view as seen through an optical instrument.

I simply am also pointing out however, that brightness of an image is only one aspect of its potential enjoyment and that the purpose of the binocular is not to increase brightness but to make the object of interest appear closer. Using an 8x binocular for example, you are able to look at a bird, a deer, etc. that is 100 yard away and observe them as if they were only 12.5 yards away. It is unlikely that most such wild animals would allow you to actually approach so close. So too, the terrain might prohibit your approach even if the object of interest in question wouldn't mind.

[Swedpat]

It might appear brighter due to both the magnification of the image and the fact that the binocular causes a bit of a tunnel effect which makes things look brighter because everything around the periphery of the image is a black circle but, this is an optical illusion.



That was exactly the same I meant with the effect of that the apparant FOV is narrower than with naked eye.
But I am not convinced that it's always just an illusion. Because the tunnel effect compared to the naked eye view will exclude some light from the outer area which is now black I think the eye really can get an increase of the perceived brightness. Especially during low light conditions.
There is also argument who pleads for that a binocular with a narrow apparant field of view may provide a brighter image than an equal powered/exit pupil sized, with wide apparant field of view. This has been discussed earlier here on Birdforum.

An example is if I am stargazing. A 10x50 with 65deg AFOV will hold more stars in the field than a 10x50 with 50deg AFOV. Though the exit pupil is the same this results in a lower total light amount reaching the eye with 50deg AFOV. This OUGHT to result in that the eyes sensitivity for the light may increase.

An example of the difference between naked and "armed" eye is if I a sunny day looking naked eye at the blue sky. If I instantly put my 7x42 to the eyes at the sky I perceive an instant eye strain because of a more intense lightning sky I feel through the binocular. Is this just an illussion? It may be, but I am more convinced when it comes to the stargazing example.

Excuse my chicken english...

Regards, Patric

[Surveyor]

Syed;

I do not pretend to understand this and could not explain it even if I did. Instead let me pose a question, actually two to consider.

1. In the attached picture, does the illuminance of the exit pupil appear to be brighter than the direct light?
2. If the metrics on the exit pupil side of the optics are all less than the direct light side, why does the tinder not ignite in ambient light?

Per your last CN post, luminance is the light falling on an object, in this case the eyes. Illuminance is the light reflected by the object, or Luminance times the reflectance, the photo in this case. In the attached photo I would assume the concrete to have a higher reflectance than the tinder. Luminace is measured at the object surface, the value falling on the surface, so it does not matter if the source is a star, the sun or a light bulb 10' away (distance independent). Illuminance can be measured at any distance, therefore inverse distance rule applies.

Confusing, isn’t it?
Have a good day.

Ron

Click on thumbnail to enlarge

[Swedpat]

Ron,

Long time ago I tried aiming the binocular, it was a 10x50, to the sun with the eyecups placed on the eyepice. It soon melted a hole on the eyepiece-cup.
Actually, I wonder: does that mean you with a binocular of 10x get the same temperature we would have beeing 10times closer the sun? It sounds logical, or? Closer to the sun than the planet Mercury, it had been HOT...

Regards, Patric

[Surveyor]

Ron,

Long time ago I tried aiming the binocular, it was a 10x50, to the sun with the eyecups placed on the eyepice. It soon melted a hole on the eyepiece-cup.
Actually, I wonder: does that mean you with a binocular of 10x get the same temperature we would have beeing 10times closer the sun? It sounds logical, or? Closer to the sun than the planet Mercury, it had been HOT...

Regards, Patric

Hi Patric;

As I stated, I do not feel qualified to explain this. But from what I have seen it has more to do with the area captured by the objective lens. For instance with a 8x20 bino I have not been able to burn a hole in paper, but have no problem with a 8x50.
Yesterday, I took a 50 mm doublet, a 60 mm biconvex and a digital thermometer outside but the conditions were partly cloudy and windy. I did not do any good with the 50 mm lens on paper but was able to raise the temperature of the thermometer from 65 degree to 175 degrees on a 150 mm x 3 mm steel shaft in about 1 minute with it. The 60 mm lens burned thru 6 layers of tissue paper in about 10 seconds.

Best,
Ron

[syed]

Illuminance is the light reflected by the object, or Luminance times the reflectance, the photo in this case. Luminace is measured at the object surface, the value falling on the surface, so it does not matter if the source is a star, the sun or a light bulb 10' away (distance independent). Illuminance can be measured at any distance, therefore inverse distance rule applies.

Ron,
If luminance is measured at the object surface then it has to change with the distance from the source of light as the intensity of light at a particular surface changes according to the inverse square law.
Doesn't in that case we find that there is not much of a difference between luminance or illuminance?
Reflectance would just be a constant quantity and hence your equation should mean that both luminance and illuminance have same physical dimensions (which can't be true).

So, I didn't get the point .
Maybe a link to a useful source will do the job.
Thanks!!

[Surveyor]

Syed;
I know that I can not explain this. But I will make a stab and think I may have a link that helps.

Deleted first example, terrible rambling reference. Far too simply stated. In general I consider that if I point a light meter toward a source that generates light, I am measuring the luminance at that point, if I point a meter at an object that reflects light, I am measuring illuminace and I know that it is far more complex than that. Hope the link helps.

http://www.crompton.com/wa3dsp/light/lumin.html

http://www.energybooks.com/pdf/D1150.pdf

Best
Ron

Since you mentioned photography, I thought of an example that may help or confuse the matter even worse. I took a light meter and measured the light falling on a wall at a picture frame. I then set the camera to that value, f2.8 @ 1/10, and took pictures at 3 distances at that setting and the spot measured looked to be exposed the same in each frame. I then took the meter to each position and measured the reflected light. They came out to be f4@1/10, f11@1/10 and f5.6@1/10 with the diffuser in place on the first set and diffuser removed on the last set. As I stated I do not really understand this myself and could be totally in error. That is why I am asking questions myself.

[iporali]

if it is then why so much hype about light gathering power of binoculars and scopes.They can't be brighter than your eyes!!


Syed,

Actually, yes they can in certain extra special cases - with the help of your eyes.

I'll take a heavily exaggerated example.
Imagine a sunny day and yourself looking at a rocky scenery, where there is a dark tunnel/cavity on the rock. Your eye pupils are stopped down at 2 mm and you only see darkness inside the tunnel. Now you take your 10x32mm binoculars and look at the tunnel. The dark view covers a larger area of your retina and your eye pupils gradually dilate: you start to see something. The eye pupil keeps dilating to 5 mm, but because the exit pupil of the binocular is only 3.2mm, your eye adaptation doesn't help anymore. Now your astro-large-bino-hype-friend hands you 10x50s, suddenly the exit pupil fills your eye pupil with light from the dark tunnel gathered by a 50mm objective and you can clearly see that hatching peregrine falcon in the darkness. "Maybe large binoculars are not just hype after all..." - or what do you think? ;)

Best regards,

Ilkka

[Surveyor]

Syed;

I found this quote in Wikipedia for Luminance.

Luminance is invariant in geometric optics. This means that for an ideal optical system, the luminance at the output is the same as the input luminance. For real, passive, optical systems, the output luminance is at most equal to the input. As an example, if you form a demagnified image with a lens, the luminous power is concentrated into a smaller area, meaning that the illuminance is higher at the image. The light at the image plane, however, fills a larger solid angle so the luminance comes out to be the same assuming there is no loss at the lens. The image can never be "brighter" than the source.

I also found a term that I had not seen before, luminous emittance, that seems more like what I consider luminance.

Best
Ron

I admit freely to being confused by the terms luminance, illuminance and now lumnous emittance (along with many other terms). :-C

[syed]

Syed,

Actually, yes they can in certain extra special cases - with the help of your eyes.

I'll take a heavily exaggerated example.
Imagine a sunny day and yourself looking at a rocky scenery, where there is a dark tunnel/cavity on the rock. Your eye pupils are stopped down at 2 mm and you only see darkness inside the tunnel. Now you take your 10x32mm binoculars and look at the tunnel. The dark view covers a larger area of your retina and your eye pupils gradually dilate: you start to see something. The eye pupil keeps dilating to 5 mm, but because the exit pupil of the binocular is only 3.2mm, your eye adaptation doesn't help anymore. Now your astro-large-bino-hype-friend hands you 10x50s, suddenly the exit pupil fills your eye pupil with light from the dark tunnel gathered by a 50mm objective and you can clearly see that hatching peregrine falcon in the darkness. "Maybe large binoculars are not just hype after all..." - or what do you think? ;)

Best regards,

Ilkka

You did try but notice that in the above example that you gave the importance of exit pupil comes out naturally but it has nothing to do with light gathering power.
Consider this:

Suppose that now after viewing the tunnel with a 10x50 bin I want an even brighter view of that tunnel. So now this "astro-large-bino-hype-friend" of mine gives me a 25x100 giant in order to further brighten the view (quite happy with the fact that this giant bin will have four times more light gathering power than the previous one).
But as soon as I look eagerly into that giant bin to get a brighter image than the previous case I found the contrary result!!!
As the exit pupil is now 4mm so I found that the view with this big bin is dimmer than the 10x50 mediocre.

So the point is still the same
WHAT HAS LIGHT GATHERING TO DO WITH BRIGHTNESS?
IT IS THE EXIT PUPIL WHICH MATTERS IN DETERMINING BRIGHTNESS.
(And that too is limited to 7mm).
Hence I still repeat
Why so much hype about light gathering power?B (:B (:

[syed]

Syed;

I found this quote in Wikipedia for Luminance.

Luminance is invariant in geometric optics. This means that for an ideal optical system, the luminance at the output is the same as the input luminance. For real, passive, optical systems, the output luminance is at most equal to the input. As an example, if you form a demagnified image with a lens, the luminous power is concentrated into a smaller area, meaning that the illuminance is higher at the image. The light at the image plane, however, fills a larger solid angle so the luminance comes out to be the same assuming there is no loss at the lens. The image can never be "brighter" than the source.

I also found a term that I had not seen before, luminous emittance, that seems more like what I consider luminance.

Best
Ron

I admit freely to being confused by the terms luminance, illuminance and now lumnous emittance (along with many other terms). :-C

I think going out and asking a learned physics lecturer is the best way out of this mystery (google seldom helps in these kind of complicated stuff.You only get more confused).
The next better way would be perhaps a book I think!!;);)

[mooreorless]

Syed, "Suppose that now after viewing the tunnel with a 10x50 bin I want an even brighter view of that tunnel. So now this "astro-large-bino-hype-friend" of mine gives me a 25x100 giant in order to further brighten the view (quite happy with the fact that this giant bin will have four times more light gathering power than the previous one).
But as soon as I look eagerly into that giant bin to get a brighter image than the previous case I found the contrary result!!!"

I am asking is this something you have done in the real world? I think you would find with the example you list being 25x compared to 10x there would be a difference of what you could see with the 25x100mm.
Kindest regards,Steve

[Fireform]

Hmmm. Let's see...

Your statement would be accurate if you had pupils 40 mm across, but I'm betting you don't. A 40mm objective lens has an area of about 1260 square mm, and the binocular focuses the light entering that area down to the area of the exit pupil, or about 20 square mm. Even figuring transmission losses of 10%, far more light reaches the eye through a binocular than reaches the naked eye. Ask any ant that was ever incinerate by a magnifying glass whether or not a lens concentrates light.