Lou Stoumen’s Sea of Hats, 1940. I count only three women in a very large crowd.

Next time you see a Ken Burns documentary, think of Lou Stoumen. It was Stoumen who invented a track that allowed a camera to slowly pan up and down while zooming in and out of historic photographs. He developed the technique for his 1956 documentary, The True Story of the Civil War, and it advanced the possibilities of film narrative. Before he moved to Los Angeles in 1945 to become a filmmaker, Stoumen was one of the supreme photographers of city life, especially the tidal agitations of Times Square. One of his most famous images, Sea of Hats, is a table of contents of urban human congestion. The bottom half of the photo is clogged up with men in fedoras. (It’s 1940: I count only three women in the very large crowd.) Above the mess of hats arise, like headlines or tombstones, signs of the times: a gigantic advertisement for Camel cigarettes (“Slower Burning CAMELS give you EXTRA MILDNESS, EXRA COOLNESS, EXTRA FLAVOR”) and a board announcing the New York Times’ latest bulletins. Another Stoumen picture, a distant overhead shot, shows Times Square in the rain, Broadway cutting across Seventh Avenue to form a gleaming “X” that marks the spot of the then-center of American culture.

The Museum of Photographic Arts has substantial holdings of Stoumen’s work, and a bunch of them appear in the tossed-salad exhibition Eyes of a Nation: A Century of American Photography, which the museum intends as a top-hits list and celebration of the photographic record our culture has kept of itself, from the late 19th Century to the present. The photos, drawn from the museum’s permanent collection, round up the usual stellar suspects — Walker Evans, Garry Winogrand, Carleton Watkins, Ansel Adams, Edward Weston, among many others — and the contents are organized according to theme: Pictorialism; Modernism; Landscape; Artistic Lens; the Urban Experience; Social Documentary. What the exhibition really expresses is photography’s scary, all-consuming appetite for physical reality, even when physical reality is conjured as a dreamy near-nothingness, as in Minor White’s 1959 picture of the Golden Gate Bridge. Of the bridge we see only one of its towers, a tiny erector-set assembly bobbing on the plump fog that hovers above the bay waters and land’s end. For White, photography was a visually induced meditative state that could transport us to spiritual spaces irreducible to material reality. He photographed the physical (ecstatically) in order to reveal the immaterial.

The exhibition visits the different sorts of investigations that photography has pursued. Photographs inquire into the self and its surround, of course, and they also inquire into the medium’s capabilities. Photography began pushing against its limitations quite early, when Pictorialism, at the beginning of the 20th Century, tried to “elevate” this evidence-gathering activity to the level of fine art. Shoot me, please, because I will never develop a taste for the way most pictorialist imagery decorporealizes the body, vaporizing flesh and bone. It was a wrong-headed “refinement” of a medium that didn’t have to aspire to fine art as it was then defined by painting and sculpture. And cheesy piety was built into the program, a piety most annoying in portraits of women by George H. Seeley, Clarence H. White, and Gertrude Kasebier, who depict their subjects as aimless maidens, matrons, and madonnas. A 1902 image of a woman’s torso by Edward Steichen, modeled blatantly after Rodin, is more interested in vague mythy eroticism than in clarity of form. (It looks like something you’d find on a Baroque church ceiling.) Edward Weston’s crouching nude, on the other hand, made ten years later, asserts Modernism’s new precision: while it defines the body’s granulated curves in graphite-black outline, it sacrifices nothing of the body’s sexual allure.

It’s a pleasurable jolt to pass from the faint evocations of Pictorialism to the assertive tonal structures of Paul Strand. Strand’s work in the 1920s paralleled the efforts of writers to purge language of obfuscation, ornament, and melodrama — clarity of tone, texture, and light was everything. The leaf edges in Strand’s Iris look like sharpened knives, and its surrounding ferns are as beautifully configured as lace. Photographic Modernism demanded finely articulated energy and design. We look at Edward Weston’s Plaster Works, Los Angeles and see not a building but a construct of chalky planes and cylinders and angles. The building itself looks modeled in plaster, and Weston is clearly reaching for some photographic equivalent to the planar inflections of Cubism.

The photographer and curator John Szarkowsky once wrote: “The world now contains more photographs than bricks, and they are, astonishingly, all different.”

Eyes of a Nation is an index to that diversity and measures what I think of as photography’s appetites. It’s a medium that devours what’s there. And the American things that are there include landscapes, guns, kids, crosses, movie theaters, crowds, and cityscapes. In the “kids” category are Helen Levitt’s pictures of New York children (while one girl menaces another, the boy behind her lifts her dress to have a peek) and Lewis Hine’s photographs that helped to reform child-labor practices. The four kids in Hine’s Sweepers and Mule-Room Boys look as if they’re posing for a line-up, and if you shuck your own oysters, see Hine’s Oyster Shuckers at Alabama Canning Co. and imagine a 12-year-old shucking ten hours a day. One subgenre of “guns” is “kids with guns,” and one of its most famous images is William Klein’s 1955 Gun #1: a boy, closely watched by another, points his gun right in our face, a bit of motiveless, homicidal fury in a pint-size package.

The day I was in San Diego to cover this exhibition I experienced one of those passages when art and life stream unexpectedly into each other. After spending a few hours in Balboa Park, I went to my hotel in Little Italy, where Carnival was getting raucously under way. Walking India Street among the loud and the tipsy, I recalled another subnarrative in Eyes of a Nation, the one that documents partying and its consequences, then and now. The “now” is a 1975 photo by Leon Levinstein of a wasted, emaciated Mardi Gras celebrant dressed only in a G-string. (But the whole point of Carnival is that it’s Fat Tuesday, right?) The “then” includes John Gutmann’s freaky 1937 images of masked Mardi Gras strutters. Stoumen, too, made pictures that get the allure of deranged night life: the club-goers in Carioca Night Club, double-exposed, blur their happy way into powdery street lights, and the drunken sailors in another Stoumen image have that too-intently focused look (“Where am I? Why am I here?”) that many of us will recognize. The party-goers mini-narrative more or less concludes with People in Gaol, a wages-of-sin image by Weegee (born Arthur Fellig and the sassiest crime photographer of the post-war years) of over a dozen semicomatose bodies in a drunk tank, dumped one on top of another like sacks of onions.

Photography has always spent a lot of energy looking at itself, at its means and methods. In the 1850s, the inventor of photography, Henry Fox Talbot, was taking pictures of his colleagues taking pictures, and over a hundred years later, Lee Friedlander created a body of angular self-portraiture where he photographs himself watching himself as a shadow on a sidewalk or reflection in a shop window. Photographers have also been deeply in love with vernacular signage, none more so than Walker Evans. His image of a penny-picture window display (Photographer’s Window Display) crowds several sheets of wallet-sized studio portraits. It reminds us that photography can be an act of intimacy or a public epidemic — or, in our own digital days, both at once. When Eastman invented the Brownie, photography finally went from being a pictorialist fine-art pursuit to the most demotic visual language in the whole wide world.

While walking through Eyes of a Nation, I was reminded that part of the enterprise of creating an archive of the democratic masses is keeping record of the have-nots. One wishes that the eyes of our nation were more steadfastly on the poor. I suppose most viewers who warmly admire Depression-era photos of the displaced and the destitute pay slight attention to those populations. A photograph has two contrary actions: in exposing experience, it seals it off. The reality of deprivation in Arthur Rothstein’s image of a migrant family in 1936 Oklahoma is locked into our sense of historicized beauty. It requires moral effort to relate that visual evidence to contemporary fact, and to reckon with the fact that, now, too, the poor are still plentifully with us, though usually they don’t quite seem to be among us. Rothstein’s picture is composed so that the last thing we see, after we do our human-interest panning of the faces of the vigilant mother and her children — guarded or shy or happy — is the pair of open scissors in the hands of the youngest. ■

Eyes of a Nation: A Century of American Photography is on view at the Museum of Photographic Arts until May 6. 1649 El Prado, 619-238-7559; mopa.org.