IF THERE IS such a thing as anti-information, it's the Sackler Gallery's new presentation of old photographs from Persia.

The show is billed as "a revealing look at Iranian society at the turn of the century." In the first place, there was no "Iran" until Persia changed its name in 1935. And although these ancient albumin and silver prints are fascinating, the captions tell almost nothing about the people and places depicted.

The photographs were taken by Antoin Sevruguin, a Russian Christian of Armenian descent who ran a commercial studio in Tehran from the 1880s to the 1920s. Thereby must hang a tale, but the Sackler doesn't tell it.

Among those who sat for him were Qajar Dynasty rulers Naseroddin Shah (reigned 1848-1896) and Mozaffaroddin Shah (r. 1896-1907), but we're told little about them. Ministers, courtiers and courtesans are included, with virtually no explanation of their roles. Ceremonies are shown, but their significance is not explained.

Perhaps most mystifying of all is a group portrait of "Nur Mahmud and His Family (ca. 1890-1910)." He was "a well-known Jewish doctor in Tehran" is all the caption says of a scene filled with 29 people, including a woman who certainly is in purdah and apparently is in a harem, although other women in the picture are barefaced.

If the Sackler didn't want to tell us anything about turn-of-the-century Persia, why did they bring it up? It's a curious lapse by this usually excellent arm of Mr. Smithson's institution for the increase and diffusion of knowledge.

ANTOIN SEVRUGUIN: Photographs of Iran -- Through May 26 at the Sackler Gallery, 1050 Independence Ave. SW. Open 10 to 5:30 daily. Metro: Smithsonian. Good wheelchair access.