I’d like to begin to explore the technical aspects of photography today.  A lot can be learned from what is ultimately the simplest of cameras, namely the pinhole camera.  You can make a pinhole camera simply by taking a pin and punching a hole in the front of a cardboard box (see the accompanying figure A) and putting some sort of photosensitive material: film, paper, or imaging chip on the opposite side.

Suppose that we have some object that we wish to photograph.  In physics books this is usually a candle, or a tree, or a minimalist arrow.  Let’s go with an arrow.  The thing is that every point on the arrow emits light rays in all directions.  However, the pinhole only allows a single ray to enter the camera.  This is true for every point of the arrow.  As a result a perfect inverted image of the arrow forms on the camera’s image plane.  The image plane, defined by the back of the box, is a distance f (for focal length) from the pinhole.  Interestingly for a perfect pinhole camera f can be any value.  Also, regardless of how far the object is from the pinhole the object is, a sharp image of it forms at the image plane.  The camera has infinite depth of focus or field.

We typically define a parameter called the f-number of the camera that defines depth of focus.  It is the focal length f divided by the diameter of the pinhole d.

I recently went to see an Ansel Adams exhibit entitled At the Water’s Edge,” at the Peabody Essex museum in Salem, Massachusetts.  I have had several such encounters over the years, and encounters are truly what they are.  Years ago I went to an exhibit at the Palace of Fine Arts in San Francisco, then again in San Francisco about ten years later, and then there was a major retrospective at the Museum of Fine Arts in Boston.  What I find interesting is how my view of photography and these works,  in particular, has evolved.

Early on I was taken by the sharpness of detail, how you can see every blade of grass or every nuance in the bark of a tree.  Sharpness in a picture relates to what we call resolution.  Later, particularly at the MFA exhibit, I was taken, really overwhelmed, by the dynamic range in these pictures.  Dynamic range, as already suggested, is the number of shades of grey between black and white in your picture.  The power of Adams; pictures, their inherent luminescence, owes widely to careful placement of the dynamic range.   This is the zone system that Adams’ created.  He would painstakingly measure the brightest and dimmest elements in his picture and then develop, first the negative, and then the print so as to just place these levels within the gamut of grey levels that the photograph allows.  Ultimately, the choice of film developer, paper developer, exposure times, and development times – not to mention some very well chosen dodging and burning in, modified the linearity of response in the final print, the so called gamma.  Linearity means, plain and simple, if I double exposure does recorded density also double.  If it isn’t then gamma isn’t one.

In the next few weeks, I’d like to explore all of these photographic elements in detail.  The point, for now, is that achieving a “technically good” image requires matching.  You’ve got to match the resolution of your lens  to that of your detector, be it digital or film, and then to the resolution of your print, be it a computer screen or printer,  And then the printer resolution needs to be matched to the resolution of the paper as the eye sees it.  Similarly you’ve got to match the dynamic range in the scene to that of the detector and then again to computer screen, printer, and paper. Again, as always, the eye is the ultimate arbiter and task master.

In the world of analogue photography Adams’ zone system was very hard to implement and exploit for 35 mm roll film cameras. Simply because it was hard to keep every picture in the roll within the same set of exposure and development conditions, there was a lot of compromising to be done.  However, just as Eastman’s invention of roll film made it so easy to take pictures, that they for the most part became bland and mediocre, digital photography, particularly if you shoot in raw format, has brought technical proficiency easily within everyone’s reach.  You are left to concentrate on artistic vision.  And as I walked through At the Water’s Edge, I came to realize that when all was said and done, Ansel Adam’s greatness lay in his vision.

The form of photography we spoke about in the last blog is called autoradiography.  You might ask whether this is really a form of photography and whether it truly belongs in a blog about photography.  The thing is that light comes in many flavors.  Light is an electromagnetic wave, much like the waves at a beach.  The distance between one wave and the next is referred to as the wavelength.  Visible light has wavelengths between about .350 microns and .750 microns.  Remember that a micron is a thousandth of a millimeter. But the spectrum of electromagnetic radiation extends beyond visible light.  Increasing wavelength we have infrared light, microwaves, sub mm waves, and radio waves.  In the other direction we have ultraviolet light, X-rays, and gamma rays.  So really we are taking a pretty narrow view, if we confine ourselves to visible light simply because that is what the human eye can see.

So suppose we had a painting that contained a pigment that contained arsenite, ⁷⁶As.  ⁷⁶ As has a half life of just over a day.  This means that if you start off with a gram of ⁷⁶As, it will give off gamma rays so fast that a day later you will only have ½ a gram, two days later ¼ gram etc. On the other hand if you have a gram of copper ⁶⁴Cu, it decays twice as fast; so a 1/4 gram after one day and 1/8 gram after two days.  So suppose you have a green pigment in a painting and want to determine if it contains arsenite, an arsenic ore, or malachite, a  copper ore, you simple place a sheet of photographic film under the painting for an an hour or so develop it and repeat the process a day and then two days later.  After 24 hours the density of the film below a green region decreases in half if it is made of arsenic or to 1/4 if it is made of copper.  Then to a 1/4 for arsenic or a 1/16 for copper after 48 hours.

It’s as simple as that, except for one thing.  There is very little ⁷⁶As in arsenite.  It is almost completely ⁷⁵As.  There’s a similar story for copper, which likes to be either ⁶³Cu or ⁶⁵Cu.  Atoms consists largely of two types of particles: protons and neutrons.  All arsenic atoms have 33 protons.  The so called isotopes differ by the number of neutrons.  In ⁷⁵As there are 22 neutrons.  In ⁷⁶As there are 23.  Now here’s the problem, natural samples of arsenite have precious little ⁷⁶As, certainly not enough to expose a photographic film in an hour.

To turn ⁷⁵As into ⁷⁶As you’ve got to shoot neutrons into your painting.  To accomplish this you have to take your painting to your local nuclear reactor and transmutate the metals in your pigments..  Most art museums don’t have nuclear reactors in their basements.  Fortunately, many physics departments do.  These are the basics of neutron activated autoradiography.  Remember this next time you want to catch a Spanish forger.

* For those who want to dig into this a bit more deeply check out Neutron Activation of Paintings.

I can’t quite remember the details, but a while back one of my Facebook friends posted a video dealing with some previously unknown Amazon tribe, or some such, losing their culture, anonymity, and homes to the press of lumbering.  The video was very sad, but viscerally didn’t ring true.  So I made some comment like “sad, if true.”  One of this friend’s friends (what does that make them to me?) fired back angrily that it didn’t matter if it was true, it was still sad.  I’m sorry, but my mother taught me that above all, and despite whatever the political agenda, the truth matters.  In my adult life I have frequently been confronted with the dilemma of whom should I go with, this guy (fill in the name) or my mother.  Experience has taught me, always go with what your mother taught you.

My mother was Sally Wolf (1917-1988).  She was not an opera singer, but she was very wise.

This desire to deceive with image manipulation is not new – witness the Shroud of Turin.  The desire to believe suspends all credulity. But let’s consider the Spanish Forger, who was a late 19^th century forger of medieval illuminated manuscript pages.  Scientists used a form of photography where the paintings were overlaid with photographic film so as to measure the rate of radioactive decay of pigments in the pictures.  The greens were found to contain a pigment called “emerald green” that consists of copper arsenite, not known to be used in artists’ paints until 1814.  The story of green pigments and their evolution in the 19^th century is itself very interesting, so perhaps another time.  As for the Spanish Forger, he won in a sense.  His forgeries are collected today for his artistry and in 2009 the Victoria and Albert Museum purchased a large collection of them.

I just wanted to say a bit more about RMONEY.  After posting last night I decided to take a look for myself.  All I did was zoom in on the picture to exam the edges.  I’ve zoomed in on the boy with the N and the boy with the E.  You can see very clearly the rectangles where the letters were pasted in, particularly in the case of the E.  Also, when you look at the folds in the fabric of the letters, they don’t register with the folds in the rest of the shirts.  So again, with a little objective scrutiny one can fairly easily label this picture as “black magic.”