RUDY ARNOLD and Hans Groenhoff shot thousands of aviation photos in the '30s and '40s, recording an industry that was taking off. Owning just about every picture the two ever took, the Air and Space Museum has unshelved a good sampling of them for "Focus on Flight: Four Decades of Aerial Photography."

Arnold, a former journalist, was the historian of the two. While official photographer for New York City's Floyd Bennett Field, he captured the image of practically every important person and plane that passed through there. There's Wiley Post leaning alongside the "Winnie Mae," before their flight around the world in 1933. And Jacqueline Cochran climbing into the last of the famous Gee Bee racers for an England-Australia race in 1934.

Groenhoff, a former fashion photographer, took an artist's viewpoint. A glider pilot, his love of flight influenced his sight. Parts of planes appear in every picture. At the Miami All-American Air Maneuvers, he not only snapped the sky trails of trick pilots, he also photographed the crowded grandstand from a vantage point under a prop plane, just to the right of a wheel.

A photo of steeplechasing in Warrenton, Virginia, shows horses and riders galloping between plane wing and struts. And if Groenhoff's clouds are particularly outstanding, it could be because, as he has recently said, he'd sometimes fly after a cloud all day just to take its picture.

Groenhoff, who retired last year, and Arnold, who died in 1966, are represented in the exhibit by 80 black-and-white photos and 80 color slides. Aero-nuts from nine to ninety will no doubt watch the slide show at great length, playing name that plane.

FOCUS ON FLIGHT: FOUR DECADES OF AERIAL PHOTOGRAPHY -- At the Air and Space Museum, on the first floor in the West gallery, through October, 1985.