A photograph, which allows for us to linger over a passing moment, is a form of voyeurism. Unlike the tradition of painting, in which the artist creates and orchestrates forms until they achieve a poetic, revelatory cohesion, photography (despite how much planning may have come into play) presents us with what was found. Painting may flirt with voyeurism, but its layered complexity has nothing to do with “capturing a moment in time.” (In fact, it was photography that dumped that baggage at painting’s doorstep.) When photography is at its best, its composition may remind us of that in painting; but a great photograph’s mysterious power lies in its ability to give monumental, contemplative weight to the causal act of looking. If painting, which teaches us to see, is poetry, photography, which encourages us to look more closely at the world around us, gives poetic possibility to everyday observation.

Walker Evans (1903–75), more than any other American photographer, gave poetic dimension to the act of looking — to the voyeuristic act of lingering over another person’s face, home, town, or predicament. His offhand ease with the camera and with his subjects (a kind of styleless style), coupled with his ability to order the world precisely within the frame, fuses into a dreamy lyricism and a candid classicism that is peculiarly American and unequaled in art.

Evans’s ordinary magic is made abundantly clear in the more than 150 digital, vintage gelatin silver, and gravure prints and book plates on view in the exhibition “Walker Evans: Carbon and Silver,” which opens today at the UBS Art Gallery. Curated by John Hill and Sven Martson, photographers who worked with Evans, the exhibition is presented by the Yale University School of Art, where Evans served on the faculty.

Born in St. Louis, Evans lived in Chicago, Paris, and New York. Self-taught, he was moved by Eugène Atget’s views of Paris and by the unadorned purity of picture postcards. In America during the 1930s, Evans not only defined for us what our country looks like — its buildings, signage, and people, both metropolitan and rural — he also contributed greatly to what and how we feel about those very subjects.

Evans’s plainspoken photography focuses on popular culture, often nameless faces, and seemingly mundane subjects such as streets, junkyards, graves, store windows, factory workers, and subway riders. His photojournalism, which never really strove to be “high” art, is an art of and for the people. It also had the power, decades later, when American artists were looking for something that was uniquely ours and ours alone, to give birth to Pop Art. But what sets Evans apart is that his photography (unlike Pop Art, which separates out and then exploits popular culture) embraces America eye-to-eye. As with all great folk art, Evans’s photography is transcendent because, straightforward and without pretense, it is not about us. Rather, it is us.

The UBS show centers on the definitive period of Evans’s oeuvre, the documentary photography he made between 1935 and 1936 when, commissioned by the Farm Security Administration to record the lives of rural families at the height of the Great Depression, he and James Agee focused on poverty-stricken Southern sharecroppers. The exhibition also includes books, including a number of editions, some of them foreign, of the book (published in 1941) “Let Us Now Praise Famous Men,” the resulting project between Agee and Evans. Here, too, are spreads, from Fortune magazine, of portraits of

Detroit laborers and of “Common Tools”; the Hart Crane book “Brooklyn Bridge,” as well as a vitrine filled with Evans’s cameras.

The 1930s period of Evans’s long career is the most familiar and oft-represented. In that sense, little new will be gained from the exhibition at UBS.The difference here (the hook, as it is) is that the curators, with digital technology at the ready, have digitally enlarged a number of Evans’s photographs to poster or mural scale. The enlarged images, also reproduced at roughly 8 inches by 10 inches, provide us with the ability to compare large to small.

One of the first images in the show is that of “Allie Mae Burroughs, Wife of a Cotton Sharecropper” (1936). Digitally enlarged to approximately 8 or 10 feet high, and facing the street, Burroughs, in a print dress and set against weathered clapboard, her thin lips tightly held, her eyes a glaze of distrust, disinterest, and depression, looks down at us. Certainly, the image will help to draw viewers into the gallery; much more detail can be gleaned; and there is precedent for enlarging Evans’s photographs. (Evans himself did so for an exhibition at MoMA.) But many of the digital images lose rather than gain power when blown up to poster or mural scale, where they can seem to have more to do with those 50-foot-tall figures that peer down at us from contemporary advertisements than they do with Evans’s inimitable magic.

Granted, Evans is such a great photographer that some of his photographs still work well when seen so much larger than what we are used to. Enlarged, some are even transformed — landscapes can feel as big as life — but bigger Evans is rarely, if ever, better Evans.

At 30 inches high,”Sharecropper’s Wife, Hale County, Alabama” (1936), of a standing, barefoot woman dressed in a flowing, ragged dress, has the grace and delicate grays of a Renaissance angel in a grisaille panel. And the figures moving within and in front of an open doorway in “Roadside Stand Near Birmingham” and in “Garage in Southern City Outskirts” (both 1936), also at 30 inches high, allows for us to see more clearly that Evans could find rhythms in nature that equal those Balthus composed in his paintings of “The Street.” But Evans’s photographs, intimate and soft-spoken, work best at an intimate, one-to-one scale, where their poetry is allowed to unfold slowly; and their wallop of a punch is allowed to sneak up on you. At UBS, Evans’s poetry at times is shouted as if through a bullhorn. Evans collected, condensed, and distilled things into images that feel completely unique and newly found. When his postcard views are made larger than life, they tend to shift back toward ordinariness.

Evans never preached or delivered messages, and when his photographs of tenant farmers take on the scale of advertisements and posters, not only do they begin to feel like out-of-scale chamber works, they also bring with them the sermonizing baggage of posters. And I cannot help but think that the main reason for the enormous enlargements in the show at UBS have more to do with because-we-can technology and contemporary taste for the gargantuan photograph than to do with the inherent needs of an Evans image.

Technically speaking, the richest images in the show tend to be the gelatin silver prints. Still, the digital images do not disappoint, and many of the prints are startlingly beautiful. The best wall in the UBS show is filled with nine wooden church portraits taken in the Southeast in 1936. Cropped and hung closely together, each façade has a unique frontal presence that relates as much to a human countenance as to architecture. The windows and doors take on the power of eyes and mouths. The piano-key rhythms of cast shadows under broken floorboards, the wavering shadows of passing clouds across clapboard, the tattered benches, forlorn steeples, and bare-bones quality of the buildings and compositions all give the photographs the raw, naked atmosphere of a person at his most vulnerable. Evans may be just taking pictures and recording information (and we feel that, too); but he presents us with the souls of these buildings.

Until November 9 (1285 Sixth Ave., between 51st and 52nd streets, 212-713-2885).