Compound vision

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Figure 3 - Cross section of a pixel on a color digital camera CCD sensor. From the Wikicommons and in the public domain.

Figure 1 – Cross section of a pixel on a color digital camera CCD sensor. From the Wikicommons and in the public domain.

We have been talking about camera lenses, those big objects in the front of your camera that form the image.  But remember that, as we discussed when we considered CCD arrays, that there is a second type of lens in your imaging system.  These are the microlens array (see Figure 1 ) that lie atop the CCD elements. The purpose of these microlenses, you may recall, is not specifically to image but rather to collect as much light as possible and direct it to the photosensitive array elements.  On camera sensor chips there is often considerable dead space and the task of these lens is to collect all this light and bring it to the sensor.  This becomes really essential as you put more and more pixels onto the chip, and you need to maximize the signal because of the limited surface area and well-depth.

Compound Eye of the House FlyThis concept of a sensor element or pixel which reads a single point and outputs a grey level, or color, but not an image, is, of course a copy of compound eyes in nature.  Figure 2 shows a the compound eye of a fly. Figure 3 shows the microlenslet array of the house fly’s eye in a scanning electron microscope.  The compound eye of arthropods provides tremendous field of view and makes the animal very sensitive to motion, as anyone who has tried to swat a fly or mosquito soon realizes.

The situation with the compound insect eye is not quite identical to that of the microlens in a CCD array.  Insects eyes are closer to what would happen if each microlenslet covered several pixels; so that you could form a crude image.  But if you think of that situation light would be coming in from everywhere and each pixel array, called an ommatidium, having a low resolution image of the whole scene.  This is the popular view of movies etc., but not really what happens.  The ommatidia are designed to limit the amount of light coming in from extremen angles.  As a result the image is only of the scene immediately perpendiculr to ommatidium.  So what the insect sees is a tiled view of its world.  Part of the key to all of this is that something that moves between ommatidia is rapidly detected, which is what the insect needs to find food and escape being eaten.

Figure 3 - Scanning electron micrograph of a house fly's eye showing the microlens array. From the Wikimedia Commons by United Nation and in the public domain under creative commons license.

Figure 3 – Scanning electron micrograph of a house fly’s eye showing the microlens array. From the Wikimedia Commons by United Nation and in the public domain under creative commons license.

The resolution of such eyes is however, very limited.  For instance, the resolving power of the honey bee’s eye is only 1/60th that of the human or vertebrate eye.  What a vertebrate can resolve at 60 feet (18 m) the bee can only resolve at a distance of one foot (0.3 m). To see with a resolution comparable to our vertebrate eyes, humans would require compound eyes about 22 m or sixty 70 feet in diameter.  All of this brings to mind Vincent Price as “The Fly, 1958.”  “Phillipe help me!”  Although I have to say that I prefer the 1986 remake with Jeff Goldblum and Geena Davis.

Spherical aberration

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Figure 1 - Spherical aberration, (top) an ideal lens, (bottom) a lens with spherical aberation. From the Wikimedia Commons by Mglg and in the public domain under creative commons license.

Figure 1 – Spherical aberration, (top) an ideal lens, (bottom) a lens with spherical aberation. From the Wikimedia Commons by Mglg and in the public domain under creative commons license.

I know that I have spent a lot of time discussing the issue of image sharpness or resolution.  It is a personal obsession.  Still if you read some of my posts on how a camera works, you may wonder why you can’t just stick a big honking magnifying glass in front of your camera, perhaps add your own toilet paper role to make it light tight, and call it a day.  Or, to put this question differently and to the point, why do we need to spend so many $$$ to get a good camera lens?  The answer to this question ultimately is that you need to correct for lens aberrations.  That’s where all the dollars go, and the first of these to consider is spherical aberration.

Back on September 16, 2012 we talked about Snell’s Law, which describes how light is bent as it moves from one medium, say air with its low index of refraction, into glass with its higher index of refraction, or vice versa.  That, friends, is really all you need to figure out what any lens, regardless of how complex its shape is, will do with light.  There are many computer programs, called ray tracing programs, that can do this for you, including one with the unlikely name of “FRED” that will do this for you, or rather for the optical engineers, who are designing all these wonderful lenses for us.

Figure 2 - A point source as imaged by a system with negative (top), zero (centre), and positive (bottom) spherical aberration. Images to the left are defocused toward the inside, images on the right toward the outside. From the Wikimedia Commons and released into the public domain by mdf.

Figure 2 – A point source as imaged by a system with negative (top), zero (centre), and positive (bottom) spherical aberration. Images to the left are defocused toward the inside, images on the right toward the outside. From the Wikimedia Commons and released into the public domain by mdf.

Suppose, as shown in Figure 1, we consider what will happen to light coming in from far away, aka infinity.  The top panel shows a perfect lens, where all of the rays come to a point focus.  In the bottom panel a ray tracing program has been used to apply Snell’s law of refraction to each ray, taking into account the shape of the lens.  As an aside this lens has one planer surface and one convex surface.  Hence, it is called a plano-convex lens.  What you see happens is that the further off center (the center line is called the optical axis) the ray is the closer to the lens it is focused.  As a result the net affect at the image plane, where the film or camera sensor lies, is that the image gets blurred.

As an aside, the condition shown in Figure 1 is referred to as positive spherical aberration.  The off optical axis rays are bent too much.  With different shaped lenes you can get negative spherical aberration, where the off optical axis rays are bent too little and come to a focus to the right of the image plane.

Figure3 - Example of an aspherical lens shape. From the Wikimedia Commons, originally uploaded by Pfeilhöhe and in the public domain under creative commons license.

Figure3 – Example of an aspherical lens shape. From the Wikimedia Commons, originally uploaded by Pfeilhöhe and in the public domain under creative commons license.

Take a look at Figure 2, which looks at what happens to a point source of light.  Remember that we are interested in points because and image is composed of an infinite number of points – que Seurat Seurat. Here a point source of light is imaged by a system with negative (top), zero (center), and positive (bottom) spherical aberration. Images to the left are defocused toward the inside, images on the right toward the outside.  The blurring of the system due of spherical aberration is clearly seen here.

This raises the question whether you can design a lens to eliminate spherical aberration, that is to be “aspherical?”  The answer is that yes you can, at least for a single wavelength or color.  And happily you can use these same ray tracing programs to design the lens shape and surface for you.  Figure 3 shows an example of an aspherical lens.  You may have seen such shapes before.  This kind of complex aspheric shape is what is used in eyeglasses to correct for spherical aberration.

There are other ways to correct for spherical aberration. One is to use multiple lenses with compensation spherical aberration.  Another is to make the lens of variable or graded index of refraction, by depositing some dopant* into the lens that alters the local index of refraction.  Such a lens is called a GRIN lens for graded index (of refraction) lens.  All of this, I hope, is starting to sound expensive, and we have only corrected for one of many types of lens aberration.

* Dopant is a fancy science word for something added in a small amount.  For instance suppose you made a lens out of calcium carbonate (calcite), you might want to dope it with small amounts, a few percent by weight, of magnesium carbonate.

 

Escape from the Tower of Orthanc

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Figure 1 - The Tower of Orthanc, (c) DE Wolf 2013

Figure 1 – The Tower of Orthanc, (c) DE Wolf 2013

OK, so we are officially in the “Dog Days of Summer.”  Let’s be quite clear about this.  While the term is generally applied to the sultry days of summer, when the temperatures are the hottest, it’s original meaning, and therefore physicist’s meaning, goes back to Roman times when the dog star Sirius rose just before or coincident with the rising of the sun.  It is, in fact, the case that due to what is referred to as precession of the equinox, this coincidental rising is not longer true.  What’s that you say?  The Earth spins on it’s axis like a top.  The top tilts slightly and the axis rotates slowly about the vertical, see Figure 2.  The top was a subject of endless amusement in Dr. Victor Franco’s classes on advanced mechanics.  This precession is also why we declare it to be the “Age of Aquarius,” the sun no longer rising on the day of the vernal equinox in the constellation of Ares, as it did in ancient times but rather in the constellation of Aquarius.

Figure 2 - Precession of a top or gyroscope. From the Wikimedia Commons and in the public domain under creative commons license.

Figure 2 – Precession of a top or gyroscope. From the Wikimedia Commons and in the public domain under creative commons license.

This is a time of wonderful late summer light in New England.  We have effectively seven seasons here, each beautiful in its own right: winter, early spring, late spring, summer, late summer, fall, and winter.  I spotted a wonderful old apple tree in a forgotten orchard meadow.  It was surrounded by gloriously golden lazy Susans.  The light was not what I wanted.  So I have returned four times in early morning, but have yet to find exactly what I am looking for, and now the lazy Susan’s are beginning to give up the ghost.

So, after another disappointing failure with the apple tree, I decided to visit my winter haunt – our local mall – to see what was about.  It is a quiet time in the mall.  Still it is fun to people watch and to search for photographic opportunities.  Mall security can get a bit testy if you snap away with a long telephoto.  But the IPhone provides a degree of anonymity.  It is already fall in the mall, and I observed the various indigenous peoples: beautiful and fashionable women who, since we are in the safety of the ‘burbs, will share a smile with you, long-legged teenage girls who, one can only hope, will find the rest of their clothes before school starts, and babies brought there to be entertained but really delightfully entertaining themselves.  They too are ever ready to share a smile or wave with you.  There are also the sulking teenage boys trying unsuccessfully to look as threatening as possible.  This included one young NY Yankees fan, who wore and A-Rod tee shirt and seemed oblivious to the possibility of abuse by hoards of Boston Red Sox fans.

I wandered past the new Microsoft store.  I was tempted to go in an find out what all the fuss about the “Surface RT” was.  I am a loyal advocate of PC products.  Perhaps it was old geezer prejudice, but there was something not so reassuring about the clerk with aqua blue hair.  I have no problem with dyed hair – but really, aqua!  It seemed a bad fashion decision and did not instil confidence that this woman would know what she was talking about.  Or maybe it had nothing to do with the young woman with blue hair and more to do with years of experience with products that Microsoft assured you that you had to have and then abandoned.

So I moved on.  And then I found it at the altar of the Lego Store, “The Tower of Orthanc!” And there was Gandalf the Grey about to be rescued by eagles.  When you have young children you make the excuse that the magic of such places is to see them again through a child’s eyes.  It is nonsense.  The reality is that you yourself still have a child’s passion, still believe in magic, but are too proud and self-conscious to venture in.  And good thing.  The glorious “Tower of Orthanc” cost $195.  The magic ended there and I bid a hasty retreat town the steps that spelled “Escape from the Tower of Orthanc.”

Figure 3 - Escape from the Tower of Orthanc, (c) DE Wolf 2013

Figure 3 – Escape from the Tower of Orthanc, (c) DE Wolf 2013

 

 

Running of the bulls

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Every year at this time we are greeted (bombarded?) by images of the “running of the bulls.”  One cannot help but feel sorry for the bulls, who seriously would rather be anywhere else.  This fails to mention the point that these primitive mythic games, shades of the Minoan Minotaur and Pablo Picasso, invariably do not work out well for the bovine participants.  Also one cannot help but exclaim something to the effect of “what morons!”

Still, I was struck today by this particularly bizarre photograph by Jesus Diges of EPA/Landov from Aug. 15, 2013, showing the traditional El Pilon bull run at Falces, Spain honoring  of the Virgin of Nieva*. The El Pilon bull run, as can be seen, is held on a very treacherous hill.  Runners have to avoid the bulls on an 800-meter long narrow slope with the mountain on one side and a rather steep cliff on the other.

I pondered a bit, as to what makes this image work against a myriad of other “running of the bulls” pictures.  I think that the first two points that catch your eye are the blood-red shirts and the lone bull, careening down the hill. The red is important because like someone thrilled by an aerialist performing without a net, there is an aspect of perverted voyeurism in all of this!   The broken diagonal of the path creates a dramatic interest.  Indeed, the composition of the photograph is very well done.  The dust tossed up by the bulls and the panicking runners creates a wonderful sense of motion.  The precarious foothold of the observers presents a sense of real danger.  Note in particular the photographer leaning dangerously over the edge to photograph the scene. Also, I find appealing the way the foreground is sharply in focus, while the lone bull and the background fades just slightly to out of focus.  The one aspect that throws the image off is the fellow in the red shirt, who prods the bulls with a rather large stick.  You realize with that, that absent this sadistic, mischievous fellow, the bulls might just stop and graze peacefully on the surrounding grass.  Still, when I first saw this gore-geous image, an immediate caption came to mind. “Uh, oh!”

*Tradition has it that in 1392 the Virgin Mary appeared to a young shepherd, Peter Amador Vázquez, at this spot in Falces.

A note from Hati and Skoll

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(c) DE Wolf 2013

(c) DE Wolf 2013

I wanted to pause and take note of the fact that today is the one year anniversary of Hati and Skoll.  It was launched on August 19, 2012 and we have now built up quite an extensive readership.  I’m talking about real people who visit the site and read the blog each month – not robots, worms, search engines, or webcrawlers.

I have tried to bring my unique physicist/photographer perspective to the site and blog.  The best part of all of this is the opportunity to see in other photographers’ work, both historical and contemporary, the incredibly varied uniqueness of vision.  On day one of Hati and Skoll, I spoke about the magic of photography.  Nowhere is that more apparent than when you marvel at the uniqueness of vision and at how many people are truly gifted.

I believe that digital photography has made it easier to master the technique of photography.  Surprisingly it has not raised the ante.  Rather it has enabled so many to express their souls and inner vision photographically.

So I just wanted to say that I am very grateful to everyone for their interest, support, and perceptive comments.  I have learned from all of you and from all of the pictures that we have discussed.

 

Faster than a speeding bullet

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You probably heard about, or seen, images were the sense of motion is captured by letting the moving object blur out against a stationary background.  I came across a really wonderful example of this today.  It is an image by David Munoz of Reuters that shows a runner stopping to photograph himself while everyone runs past him in exquisite blurs. This picture was taken on August 11 at the “City2surf” footrace in Sidney Australia.  There were 80,000 participants.

A number of associations come to mind: the comic book “The Flash” and a Star Trek episode called “Wink of an Eye,” where there is a parallel universe where everyone moves at incredible speed relative to “normal” life on the Enterprise.

The picture is brilliantly executed.  I love the way the image axis lies along the diagonal.  The pastels are marvelous.  And a really nice element is the way that the photographer has captured the runners’ shoes.  The contrast between the still runner and everyone else adds a perfect sense of contrast.  This is beautifully executed!

Toilet paper roll dioramas

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Yes, you read that right.  I want to speak today about toilet paper roll dioramas.  A diorama is a small scene created in a small place, like a ship in a bottle.  Small is actually not a requirement of the genre.  When I was a little boy – sorry more tales from the cretaceous – I loved to go the the American Museum of Natural History and when I got home I would use little wooden cheese boxes and plastic animal figures to create my own natural history scenes, or I would invert small plastic strawberry or blueberry containers from our local Pioneer Market to create little zoos.  A more complex contrivance was to take a cereal box, cut a square hole at one end, and an eye hole at the opposite end, and to string a comic strip between two pencils that would stretch across the square hole.  Hold it up to the light and you slowly wind the comic strip in succession and create a kind of miniature movie.

Carrying all these memories, I was delighted this week to come across the simply magical worlds of French Artist Anastassia Elias.  These are magnificent and complex dioramas each contained within the telescopic universe of a toilet paper roll.  Click on one of the images and then click on the right arrow to see a slide show.  I’ve decided that the photos are just as wonderful as the dioramas themselves, which makes it all fair game for Hati and Skoll.  Enjoy these little marvels that ultimately take us back to childhood, when anything was possible and all possibilities were magical.

Twittering away your photo rights

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Many of the readers of this blog access it through Facebook – no fuss, no muss.  There are two user groups on Facebook that I also enjoy: Large Format Photography, and Strictly Black and White.  You post your images there and people give you the I Like thumbs up or even comment on your work.  Again it’s no fuss, no muss.  Well maybe not so much.  I started worrying about who owns the rights to what I post on Facebook.  So I checked out the Facebook Terms of Service.

These clearly state the following: “For content that is covered by intellectual property rights, like photos and videos (IP content), you specifically give us the following permission, subject to your privacy and application settings: you grant us a non-exclusive, transferable, sub-licensable, royalty-free, worldwide license to use any IP content that you post on or in connection with Facebook (IP License). This IP License ends when you delete your IP content or your account unless your content has been shared with others, and they have not deleted it….We always appreciate your feedback or other suggestions about Facebook, but you understand that we may use them without any obligation to compensate you for them (just as you have no obligation to offer them).”

What all this means is that while you retain ownership of your photos, in fact of anything you post on Facebook (Pretty much the same applies on Twitter.), they can use it however they want and can transfer those rights to anyone else.  Psst, this means they can sell your images. If you post a cute picture of your baby, don’t be surprised to find it in an ad campaign somewhere.

But, you say, I can always delete it.  Good luck with that!

An important bottom line here is that you are granting a nonexclusive license.  You can still sell or allow a nonexclusive license to someone else.  That’s all fine and dandy, except that you might want to sell an exclusive license to someone (an exclusive license is one where you grant, hopefully for a huge fee, the rights to your picture and you promise not to sell or grant it to someone else). Not being able to do that diminishes the value of your property.

All of this may or may not seem threatening to you.  People are starting to recognize that privacy is an illusion.  It is however, important to understand your rights.  It’s all part of the democratization of the internet and social media that I keep talking about.

One solution that many people use is to only upload lower resolution images (lower than your best) and to write a big honking watermark on them that bears and proclaims your name or copyright.  It doesn’t change your rights, but it does make you feel better,

For more on this subject see this website by nyccounsel.com.

Marking the end of celluloid film

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I recently posted about the early nitrocellulose-based film that really marked the beginning of the movie film industry – and what a ride it has been.  Well, we are now really on the other end of it all.  2013, perhaps 2014, are widely expected to usher in the end of what is generically referred to as celluloid based film.

In 2011, Fox announced that it would suspend production of film-based movies by 2013, and worldwide 90,000 theaters have converted to digital projection.  Fujichrome delivered its last film stock this past March, and this leaves only Kodak, which is pulling out of the film business as it emerges from bankruptcy.

Should we be sad?  The story is a lot like that of digital photography in general, and it’s all really a matter of what is referred to as Moore’s law.  The law is named after Intel co-founder Gordon E. Moore, who in 1965 described the fact that the number of transistors we can put on a circuit board doubles every two years.  More often it is quoted in terms of a computer performance doubling every 18 months, this because performance depends both on the number of transistors and how fast they are.  As regards photography the point is that when digital photography was introduced images didn’t have the dynamic range or resolution of film.  But it was only a matter of time because of Moore’s law.

We now have the resolution of film, greater dynamic range than film, and unbelievable processing capability.  Compared to film cameras a few decades ago, which had simple light meters that controlled exposure and focusing, today’s DSLR’s are essentially computers onto themselves.  Distributing digital copies of movies is a tenth the cost of distributing film copies.  The special effects that we love so much are easier and cheaper to produce.  Indeed, as we’ve seen you don’t even necessarily need actors and actresses.  It can all be done by computer.  And as we’ve discussed previously all of this means that there is a growing democratization of film production, and film distribution via the internet.  The bottom line is that the technical, creative, and financial aspects of the art are all significantly enhanced.

So as regards the question of whether we should be sad, the answer is probably not.  My one caveat here is that as media succumb to financial pressures and necessity, whole genres of human creativity become lost.  I remain a great lover of silver gelatin photography, and platinum printing, and daguerreotypes.  A number of years ago I went to an exhibit of the work of Chuck Close, where side by side were shown portraits in hologram and daguerreotype and I was left with the realization of how wonderful it would be if daguerreotype printing were still more readily accessible to artists.

Most writers on the subject say that film will never die completely.  I am not so sure.  Roll films, celluloid movie films, are technically complex to produce.  As demand plummets, it seems very likely that financial pressures will drive them to extinction.

I can remember seeing movies as a child, when all of a sudden the image on the screen would melt before your eyes from the heat of the projector. There is a Mash episode that depicts this.  I definitely won’t miss that!