Seeing

On Seeing Further

cevans — Mon, 13 Jun 2011 11:45:00 +0000

On Seeing Further

"All things move and nothing remains still" -- Heraclitus

The history of astronomy can be read as a story of better and better vision. Over the centuries, we have supplemented our vision with technology that allows us to see further and more clearly; while Ancient astronomers, who relied only on their naked eyes to perceive the universe, managed to make star catalogues and predict comets, Galileo, pressing his to a telescope, saw all the way to the moons of Jupiter.

Optical telescopes and the human eye are fundamentally limited; early astronomers were forced to gaze into telescopes for hours on end, waiting for moments of visual stillness long enough to allow them to quickly sketch drawings of the features they were simultaneously trying to understand. Between a telescope (incidentally, "telescope" is Greek for "far-seeing") and the celestial bodies beyond, the Earth's atmosphere itself is in turbulence, the optical refractive index bleary -- which presented early astronomers with a view of the universe that was blurred, twinkling, always in flux. This is because the sky is not transparent. Thermal currents passing through the Earth's atmosphere cause air density (and hence the refractive index of air) to vary, to warble like a desert mirage. Light does not pass through this unaffected. Quite the opposite, in fact -- thermal currents are like thousands of lenses floating around in the air. We call this phenomenon "astronomical seeing," and it's why stars sparkle, why even the moon seems to be swimming in water when peered at through an optical telescope.

It wasn't long before Galileo and his fellows had seen as far as their technology -- and their vision -- could reach. In the years to follow, new far-seeing tools popped up as needed: X-ray telescopes, gamma ray telescopes, high-energy particle telescopes, even telescopes floating in space. As time progressed and our science grew more refined, we tried wavelengths previously unnoticed; we paid attention to new qualities; when we thought we'd seen it all, we looked again, our vision evolving beyond biology as we began to "see" with technology.

The inevitable result was that though the physical universe never changed, we did, because we looked differently.

This different-looking triggered perhaps the most important conceptual leap in the science of the 20th century: the realization that there is more to reality to what can be seen. The years between 1880 and 1930* saw massive upheavals in the way science was conducted -- during this period, we moved from the strict empiricism of Newton to the reliance on unobservable and theoretical constructs that dominates the discipline today. We began to peer into previously unseen worlds; we parsed the structure of the atom and discovered elementary particles. Once we were there, our physics no longer had bearing. We needed to invent and codify new ways of seeing, ways not dictated by observable phenomena; and so our understanding of time and space gave way to general and special relativity, quantum mechanics, and alternative geometries. The intellectual legacy of this radical change -- and its relevance to my point here -- is in the primacy it lends to subjectivity, to not only the instruments of seeing, but those who peer into them.

Astronomy, too, zygoted in the early 20th century. Photography solved the problem of hand-drawing findings between patches of blurry sky. Infrared, radio, X-ray, and finally gamma-ray astronomy came to prominence, filling our coffers with surreal images of a previously invisible world. We used spectroscopy to study stars; our sun was found to be part of a galaxy, and the existence of other galaxies was settled by the great Edwin Hubble, who identified many others, rapidly receding from our own, at impossibly large distances. We created the model of the Big Bang. We stumbled upon cosmic microwave background radiation. All of a sudden, the story of the universe as we knew it vaulted out of the visual world and into a rich and million years-long narrative of unseen forces and galaxies so distant they bordered on theoretical abstractions. Like science itself, visual perception of the cosmos evolved from the physical to the theoretical; when we speak of "seeing" astronomical images, we're talking about a highly mediated experience, captured by mechanical sensing devices, where invisible qualities are color-coded into something the human eye can register as information.

The eye is almost universally a symbol of intellectual perception; in Taoism, in Shinto, in the Bhagavad Gītā, the eyes are the sun and moon. Is it any wonder that the ancients conflated astronomy and astrology? That those who look out at the universe have so often been mystics, seekers, and seers? We speak of "visionaries" in all fields as people who are capable of seeing furthest -- beyond the blurred intermediary of the physical world and straight to the heavens.

Optical, radio, X-ray, and WMAP all-sky images. Images via online sources, animated GIF by yours truly.

*As an interdisciplinary aside: this period was simultaneous with the rise of modernism and abstraction in the arts. Could this movement from the pragmatic and visible to the invisible and conceptual be attributed to a common zeitgeist? Could it be that the early 20th century saw an unprecedented amount of cross-pollination between the arts and sciences, leading to a moment of cultural fertility?

Read this article on the World Science Festival blog here.

cevans Mon, 06/13/2011 - 07:45

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Kindle vs. iPad in the Sun

rallain — Thu, 12 Aug 2010 07:43:05 +0000

Kindle vs. iPad in the Sun

There is this commercial that has been coming on lately showing some people reading the Kindle at the beach. Why is this a selling point? It has to do with the way the Kindle works compared to something like the iPad. I would take a picture, but I have neither of these devices. Instead, I will make a diagram.

Maybe you can't tell from my diagram, but I am using the black rays to represent light reflected from the Kindle and red rays to represent light produced from the iPad. And that is the key. The Kindle does not have a light source, it is very similar to a piece of paper. The iPad is kind of like a flashlight in that it is a light source.

So now, you are in the bright sunlight. For the kindle, the brighter the external light source, the more light is reflected. This is good. Your eyes adjust to bright light to not let as much light in. The result is that you can see the Kindle just fine in the sunlight. The iPad only produces a finite amount of light. The brighter it is outside, the less you can see it. First, your eyes are adjusting to just looking at brighter things (so that doesn't help). Also, there is more light reflecting off the surface of the iPad making it harder to see the image below the glass (this is just like looking through dark windows.)

In the opposite case - in a dark room, clearly the Kindle is at a disadvantage. You need some external light to view it and read in bed. This is actually better for your eyes (so I am told), but it might disturb anyone else in your bed that wants to go to sleep.

In the end, I have neither of these devices. I still read dead-tree books. Oh, and I doubt I would ever take even a book to the beach. It's not that I don't want to relax, I would just rather play or dig a big hole.

rallain Thu, 08/12/2010 - 03:43

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Dead tree books don't have backlights either. They have a little more contrast than a kindle, and use even less power. But a Kindle holds way more books per cubic inch, and you can read it with one hand without a holder.

Oh- and you can always turn the light on to read the Kindle, but you can't turn the sun off to read the iPad.

The link you provided in the text is broken. The correct link shoulb be looking through dark windows.

Thanks - it was a link typo. I fixed it.

Amazon investors are scared of the iPad, The iPad has had a major impact on the price of shares of Amazon in recent months, as investor sentiment for Amazon has been waning ever since the iPad was released - http://tinyurl.com/35aw49r

That's why I'm still waiting for a smartphone that uses e-Ink technology. I cannot use my cell phone in the full sun. I can dial numbers and call people on it but I cannot read the menus or the lists of phone numbers.

It seems to me there is a profitable (not the same as largest) market for actually usable outdoor cell phones.

Any thoughts on the upcoming Mirasol screens from Qualcomm? Having color capabilities in a reflective screen seems like a game-changer.

For the iPad there are some Anti Reflection folio for the display. It works perfect. Only some colour brilliance fade away. But you can look at the display with direct sun lightning. and the fell of touch is better too.
Best regards

My brother was being an idiot about this. He was going with a lot of other idiots on the web saying the reason was because of the glare. NOT true.

The reason is the type of LCD they use in the devices. The kindle uses and oldschool reflective LCD -- almost like the ones you find in cheap watches and the old Game Boys. This type of LCD looks grey-greenish when the unit is off (or even when it's on provided the LCD screen isn't all black).

The iPad uses a back-lit LCD screen. These things look black when the unit is off. They're the choice for notebooks and similar devices because they give better colour and contrast.

You don't need backlighting to see whats on a reflective display because the light reflects off the back of the lcd. However, because it doesn't produce light of its own, you won't see it at all in the dark.

On the other hand, you can't see back-lit lcds in intense light (such as sunlight) in the same sense that you can hardly distinguish the shine of a flashlight in an open field under the sun. The sunlight is just so much brighter and yes -- your eyes are adjusting to the brighter light.

Some devices like video cameras have reflective - backlit screens. You can use them outdoors without the backlighting or indoors with the backlighting on to provide visibility. Again, just look at the colour of the screen when the unit is off to quickly see whether it's a reflective screen or a non-reflective one.

The whole light-reflecting-off-the-glossy-screen is not the main reason why you can't clearly see the iPad under the sun. Try it with any notebook and see for yourself. Then try shining a flashlight at the ground with the sun out.

Here is how to use the iPad as e-reader under direct sunlight.

1) Use white text on black background mode
2) Use maximum brightness
3) Use polarized sunglasses.
4) Move it around a little for better result.

Below is example.

http://www.youtube.com/watch?v=NksXmYdji1A

I'm currently reading a book in the sun on my iPad next to my girlfriend reading a good old fashioned dead tree book. She has to wear dark glasses, and I do not - one small advantage of having a screen with lower contrast I guess!

I am thinking of getting my wife a kindle to read on holiday in Turkey, which I am hoping will be sunny. I had a look at the screen in the shop and it does look totally different to an ipads. Also part of the reason she wants a kindle is because she thinks its lighter than a book to hold as she has arthritis.

Why is it dark inside?

rallain — Mon, 12 Apr 2010 21:07:39 +0000

Why is it dark inside?

This was a great question. When you come inside after playing in the sunny outside, why is it so dark?

Simple answer: because your eyes are smart. When you are outside, there is a lot of light. Really, it is too much light. To compensate for this, your pupils (the part of your eye that light goes through) closes some. And then, when you go back inside your pupils are still small. Inside (even with the lights on) is not nearly as bright as outside. Not enough light is getting through your pupils and so everything looks "dark".

Here is a simple demo. While inside, take a flashlight (not too bright - just a plain one) and shine it in someones eye. Watch the eye and you can see the pupil get smaller. I showed this to some kids and they thought it was awesome. Here is a video.

rallain Mon, 04/12/2010 - 17:07

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As Ben Goldacre would say "I think you'll find it's a bit more complicated than that".

Pupil reactions are part of the story, but there's some other equally awesome anatomy, biochemistry and neurophysiology involved.

The diameter of a typical young person's pupil varies from about 2mm in bright light to about 8mm in the dark (older people's pupils don't dilate quite as much in the dark). Since the amount of light entering the eye depends on the area of the pupil, this increases the sensitivity of the eye about 16 times. This 16 times improvement is pretty impressive, until you realise that the human eye can adjust its sensitivity by a factor of about 1 million!

Obviously there's other stuff going on.

One factor is that the eye adjusts its response to light by utilising a form of "gain control" in the nerves in the retina. The signal being sent to the brain is adjusted to allow for the overall brightness. When you come inside into a darker area, the signal is "turned up", so that your vision becomes more sensitive. This doesn't happen instantly, so things appear dark to begin with, but quickly start to appear brighter.

Another mechanism for adjusting the sensitivity of the eye is the regeneration of photopigments in the photoreceptors (the light-sensitive cells in the retina). Photopigments are molecules that change shape when they absorb light, setting off a chemical reaction that ultimately results in a nerve cell sending a signal down the optic nerve to the brain. Once a photopigment molecule absorbs a photon, it takes a while (and some fancy biochemistry) for it to change back to its original shape, "resetting" it so that it is ready to react to light again. When you come inside there are fewer photons hitting the retina, so more photopigment molecules can be reset. This is a slower process, so your vision becomes more sensitive over a period of a few minutes.

A fourth mechanism comes into play if you move into a really dark area. Your eyes have two types of photoreceptors, known as cones and rods. The cones work well in brighter conditions and allow for colour vision because there are 3 types of cones that respond differently to different wavelengths of light. Rods don't work well in bright light, but are very good at detecting small amounts of light. Because there is only one type of rod they can't distinguish colours, and because of the way they are spread out over the retina they aren't very good at seeing fine detail.

As the light gets dimmer, it reaches the point where the cones can't detect the light anymore. At this point the rods take over, allowing the eye to detect very dim light at the cost of losing some detail and colour vision. You can observe this if you go into a dark room (or turn off the light at night). Initially you can't see anything, but if you wait you can gradually start to make out shapes. After a few minutes you can see quite well, although not as well as with the lights on, and everything is in shades of grey, not colour.

BTW, there's another cool trick you can do with pupil reactions that doesn't depend on the amount of light. If you look at your eyes in a mirror, and then move closer to the mirror, your pupils will get smaller. The size of your pupils is linked to where your eyes are focussed - the closer you focus, the smaller your pupils.

photon

The previous descriptions have all missed perhaps the most critical part of the light adaptation story in the vertebrate eye:

One of the last steps of the phototransduction cascade is the closing of cation channels in the photoreceptor cell membrane in response to light stimulation. For small amounts of light this has the main effect of hyperpolarizing the cell slightly, which decreases the likelihood of neurotransmitter release onto the target cells that pick up the signal for further processing. However, with a large quantity of light hitting the receptor, the closing of the cation channels may significantly reduce the intracellular concentration of calcium. Reduced intracellular calcium in turn upregulates the hydrolysis of GTP to cGMP by the guanylyl cyclase. Increased concentration of cGMP causes more cation channels to open and thus resets the dynamic range of the cell's response curve.

I can understand though how this step is easy to miss, the others being more intuitive.

Seeing through windows - light and dark

rallain — Thu, 14 Jan 2010 17:20:27 +0000

Seeing through windows - light and dark

Here is a picture of something you have seen before.

These are two pictures of the same location in my house. The one on the left is taken when the Sun was up outside and the other one when it was dark outside. For both pictures, I had the same lights turned on inside. So, why does it do this? Why can you see stuff outside when it is bright outside, but you don't see a reflection of the stuff outside? Why when it is dark outside, does the opposite happen? You know what I am going to do next, right? Diagram. Here is a diagram for when it is dark outside.

The person can see the blue box because the light from the lamp reflects off of it (I drew that light as blue arrows).
When light hits the window, some of it goes through the window and some reflects off the window.
Some of the light reflected from the window goes to the person so that the person can see a reflection of the blue box and the light.
Some of the light goes through the window. So, if you were outside in the dark, you could see the light and the blue box.

Now, what if it is not dark outside.

Now there is a lot of bright light outside (from the Sun). This light reflects off the giant red monolith that just happens to be there. Again, some of that reflected light goes through the window so that the person can see it. Some of that light reflects off the window also. The person inside can see the monolith, but this light is too bright for the person to see the reflections from the inside of the room (but they are still there).

If the inside light is not too bright, a person on the outside could not see inside because the light reflected from the outside is too bright. The light from the inside is still getting out, it is just too difficult to detect.

This is essentially how a one-way glass works.

rallain Thu, 01/14/2010 - 12:20

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When I was a little kid I was amazed to realize that when I was up inside a tree (in the summer) I could see somebody looking for me but they couldn't see me. It took a while for me to work it out that I was in deep shade, hidden behind the glare of the leaves, making me invisible, while he was in broad daylight.

It was only a little later that I waved through the window to somebody outside through, but they couldn't see me until I moved up close to the window.

Nice connection of how one-way mirrors work to everyday experience.

In my evil-scientist-with-enormous-financial-resources dreams, I make all my one-way windows using faraday rotation and polarizers. True one-way viewing! Of course, in my dreams I've also invented a broadband faraday rotator.

Net curtains are so sneaky. When you can't see out of them, that means other people _can_ see in.

For one way glass the surface of the it is so shining with extra polishing materials that effect on reflection methods. If you are outside and inside room is having same brightness then also you ca not see any objects inside the room. because the shining surface does not allow the sunlight ray to pass through the glass. It is completely reflected.

Views from Physics Tutor

I very informative piece.

Okay, can you explain how the two-position rear-view mirror works? You know the device, some idiot drives behind you with his high-beams on. The light from his headlights, reflected from your rear-view mirror, blinds you. You reach up and flip the little lever that tilts the mirror in a specific way and the light is no longer in your eyes but you can see behind you. A bit dimmer but you can still maneuver.

off the top of my head, without resorting to looking at my rearview mirror, i'd say that the two position rearview mirror in normal position reflects light mostly off the shiny surface off the back of the mirror. when you flip it, you change the angle of the shiny mirror so you don't see the refllction. instead you are seeing the reflection off the glass front of the rearview mirror.

since shiny mirrors reflect near 100% and glass only about 7 or 8%, the bright lights look dimmer in the flipped position.

That sounds good Rob, I appreciate your trying, except for one small catch. Unless the mirror was made in a very special way, perhaps if it was wedge shaped in cross section, wouldn't the front and back surface of the glass be parallel? And if parallel how would tilting the mirror, which is what the lever does, shift the reflective surface used from one to the other? Or have I failed to understand some basic concept?

I feel a bit foolish not knowing what must be some very basic scientific principle that allows this simple device to work but it remains quite mystifying.

To expand on what rob was saying:

The shiny mirror surface is still there, and would still be reflecting light better than the "secondary mirror", but of course now it's pointed away from the rear window (pointed up?) and there is less light reaching your eyes by that path than light coming in through the rear window and reflecting directly off the secondary mirror. That's why you still see the car behind rather than the interior of your own.

(The details of how you switch between the two is engineering, and therefore not a "catch", but some other blog's problem.) :-)

Re: rob and Art at 6 & 7

You're both right of course - the glass is wedged. You can verify this yourself by moving your head up and down to see both reflections.

Unfortunately I can't do this myself in my current car - I've got one of them newfangled auto-adjusting mirrors. Soon the toggleable glass wedge rearview mirrors will be a thing of the past.

A demo for the color black

rallain — Wed, 08 Jul 2009 13:35:01 +0000

A demo for the color black

What do you see when you are in a completely dark room with no lights?

That is a great question to ask. It can bring out some interesting ideas. Anyway, here is an easy demo to show the color black. The basic idea is to build a box that has a small opening. Here is what it looks like from the outside:

As you can see, just a basic box. I have a door on the top, and I put a paper towel tube for a window. To make it look pretty, I covered it with black paper (so you couldn't tell where I stole the box from).

To demo this to students, I first go around and let everyone look inside. I ask "what color is the inside?" Most people will say black, but some will say "I can't see anything". If you press them, they will agree it is black (stress - what color is it?). This is what they see:

The next step is to open the door on the top and let them look inside. Or, if you like, you can ask what color the inside of the box actually is. The real reason I colored the outside of the box black is so that they would perhaps assume the inside is also black. With the door open, this is what a student would see inside:

In case you are curious, that is a picture of me with a burger king crown on (long story). You could put anything in the box that you think is amusing. Hopefully, students 'see' that if no light is reflecting off my image, then you won't see it (which is what we call black). This box is actually a type of black body. Although light does go into the tube, it gets absorbed a little each time it reflects off an inner wall. By the time any light would reflect back out, it has been mostly absorbed.

Here is the next-level question:

Suppose I mount a mirror on the back wall of the inside of the box. If you keep the top lid closed and look in, what would you see?

Here is a picture if you can't handle not having the answer. As a note, I put a platter from a hard drive back there and had trouble lining it up. But you get the idea.

rallain Wed, 07/08/2009 - 09:35

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Rhett - you come up with the coolest blog posts! Great stuff - really stimulates the synapses in the noggin' to ponder such things!

Awesome! I was initially confused by the picture with the mirror, but I get it now after a bit of thinking. Thanks for sharing!

Ligtly bolt together a registered stack of degreased double-edged razor blades. Be careful not to ding the sharp edges. The two sharp sides are eye-sucking black despite (because of!) the polished mirror blade edges. (Store with silica gel desiccant - they rust.)