Delineating the exceedingly subtle difference between naturalistic and pictorialist photography is one of those scholarly exercises that only a connoisseur would cluck over. That would be Christian Peterson, the acting curator of photography at the Minneapolis Institute of Arts, who has mounted a nostalgic show that does just that.

"Peter Henry Emerson and American Naturalistic Photography," which opens Saturday, offers about 80 landscapes and genre images by 24 naturalistic artists working between 1890 and 1930. All are Americans except Emerson, an Englishman whose books and portfolios -- often lavishly illustrated with platinum prints or photogravures -- helped define the field for progressive amateurs and professional enthusiasts in the United States.

Emerson, a distant relative of American philosopher Ralph Waldo Emerson, was an early influence on Alfred Stieglitz, who went on to become one of the most important photo promoters and art dealers of the early 20th century (and, not incidentally, to marry Georgia O'Keeffe). The show and its very pretty catalog ($39.95, published by the institute) include a couple of early Stieglitz photos in a sentimental, moralizing, anthropological mode -- one of a barefoot peasant girl resting in a field against a bundle of firewood, the other of a bonneted woman mending nets on a beach.

The other big-name American is Edward S. Curtis, whose 20-volume ethnographic and somewhat romanticized record of American Indian tribes staked his claim to photographic immortality. Several Curtis images are shown, including a quite handsome gravure profile of Bear Bull, a Blackfoot with an impressive topknot of hair.

Peterson contends that Curtis falls into the "naturalist" camp because of the similarities between his work and Emerson's. Like Curtis, who artfully documented the lives of Indians, Emerson brought ethnographic rigor to his studies of the peasants of England's Norfolk Broads, a marshy coastal region where industrialization threatened rural values. Both accompanied their images with extensive writing about the culture and lifestyles of their subjects.

Naturalism vs. pictorialism

A Cuban-born, English-educated doctor, Emerson devoted his career and independent income to the promotion of photography as an art. His 1889 book "Naturalistic Photography for Students of the Art" was enormously influential. Reacting against the prevailing taste for sharp-focused allegories patched together from several negatives, Emerson insisted that photographers should stick to Nature with a capital N.

That meant rural subjects such as landscapes, agrarian lifestyles and rustic domestic scenes. He advocated sharp focus for a photo's main subject and softer focus for background and edges, an approach that he believed imitated human vision, but was controversial among photographers.

The pictorialists, a successor art movement, often took the soft-focus aesthetic to extremes of muzziness as they self-consciously positioned themselves as artists. Their compositions were also more formulaic and imitative of paintings. Emerson, too, was influenced by art, particularly French Barbizon painters J.B. Camille Corot and Jean-Francois Millet, whose solitary peasants in evening landscapes echo in the show's photos of farmers haying and gathering reeds.

The photos

There are some lovely compositions in the show and catalog, notably Emerson's iconic "Gathering Water Lilies," which inspired William B. Post's "Summer Days," a lyrically stagy scene of a woman in a boat plucking a lily from a pond. Henry Troth's "In Springtime, Pennsylvania," is an exquisite platinum print of woods and a flower-filled meadow. Sarah J. Eddy's "Sunny Kitchen" is, likewise, a Vermeeresque hymn to wash-day drudgery wherein a woman bends lovingly over a tub of dirty clothes as though worshiping a newborn babe.

For all its scholarly bona fides, this is a really boring show. Very few of the photos have any intrinsic interest and a great many are excruciatingly banal, treacly, moralizing or sentimental. Also, given the slow photographic technology of the time, virtually all are staged and therefore preposterously artificial and frozen despite their claim to "naturalism." See especially Emerson's own "During the Reed Harvest," John G. Bullock's pictures of cats on a stoop and a girl feeding a pony, Harry G. Phister's antique wooden wells, Eddy's ridiculous old gent by a fireplace, William E. Dassonville's hymns to muddy roads and virtually all the landscapes.

Even making allowances for changing taste and the narrowness of the show's premise, this is the sort of tedious stuff that would try the patience of a dissertation committee. One must applaud a museum for encouraging the investigation of scholarly byways, but it would be infinitely more rewarding if the paths went somewhere of interest outside academe.

Mary Abbe • 612-673-4431