LAST week, early on a clear sunny morning in Philadelphia, photographer Paul Hosefros and I stood in front of Independence Hall making exposure calculations, checking camera angles and attending to all manner of major and minor details. Every so often Hosefros stopped to go live for an interview on local radio and TV.

The attention and hubbub, as work-bound Philadelphians whizzed by us on buses and in cars, was caused by the photograph Hosefros plans to make on July 4 for the city of Philadelphia. It's an ambitious group portrait -- you might call it a portrait of America at the Millennium -- that the city has modestly billed as "The Photo of the Century."

Hosefros, an award-winning photojournalist and senior Washington photographer for the New York Times, has been hired by the city to make a huge group portrait of more than 100 people in front of Independence Hall on Independence Day. But these won't be just any 100 folks. Each was born on the Fourth of July -- and each will represent a different year of the 20th century. That means a crowd ranging in age from 100 to just born.

That also means one of the most difficult -- if also enjoyable -- photo assignments of Hosefros's long and distinguished career.

Over the years Hosefros has covered any number of Independence Day celebrations in Philly for his newspaper -- Independence Hall, the Liberty Bell, etc., being natural backdrops for presidents celebrating the holiday -- and he has gotten to know several Philadelphia officials in the process.

Last March, Hosefros noted, one of them called and said, "Hey, what are you doing on [this] Fourth? Wouldn't it be great if you could come up and take a picture."

"I thought it was going to be a case of bring a camera, take a picture -- case closed."

But it took only one meeting for Hosefros to see just how ambitious the project was to be -- and how technically challenging it would be to pull off. Happily, over the ensuing months, Hosefros got a ton of technical help -- not to mention advice from friends and colleagues -- and went into last Monday's technical run-through confident that he had amassed both the photographic know-how and top-of-the-line equipment to pull it off.

There were at least a dozen of us outside Independence Hall that day. [I've known Hosefros for nearly 20 years and eagerly signed on as a second set of eyes and hands as he met with his team.] Besides a host of city officials, there was Terry Deglau, manager of trade relations from the professional division of Eastman Kodak, the main sponsor of the Philadelphia event; Tony Corbell, corporate communications manager for Hasselblad USA, who showed up with a caseload of cameras and lenses that I happily would have swiped; and John Shirilla, sales manager for Photogenic professional lighting, the chief lighting consultant for the big event. Also in Hosefros's corner was 32-year-old New York photographer Mike Nemeth, a lighting and technical wizard who has assisted some of the biggest names in commercial and editorial photography, including Fred Conrad and Andrew Eccles.

For the better part of an hour, we measured and calculated. For the Fourth, stepped risers will be built in the street in front of Independence Hall so that none of the subject's faces will be obscured in the photograph. [The plan is to have the crowd dressed either in red, white or blue and to hold tiny flags and sparklers.] Though I initially thought we would have to use an ultra-wide angle camera like the Hasselblad Superwide CM, a medium wide 50mm lends on a Hasselblad 503 CW filled the bill perfectly, as demonstrated by Tony's test Polaroids that morning.

Lighting a picture like this means more than providing flash fill to augment sunlight. Hosefros insisted that flash be the main light source, not only to freeze his 100 subjects, but also to give him greater creative control. It was widely agreed that so large a group would have to be shot at an optimum working aperture of f.22 -- meaning that there would have to be a boatload of strobe power available -- fed by hefty portable generators.

Though Hasselblad will be the main camera choice, Hosefros plans to take the photograph simultaneously in other formats as backup. There will be a color and black-and-white version made in 4 inches by 5 inches, as well as a digital 35mm version. For the main photograph, three Kodak films were chosen -- each to be loaded in a separate Hasselblad back and used on the same camera to assure identical camera position. The first exposure will be made on Kodak's great new color print Portra 400VC film. The second will be made in black-and-white at the same exposure setting on T400CN. The final picture, on transparency film, will be made on the ultra-saturated Kodak E100VS.

Obviously, the logistical hassles for a picture like this are many. Hosefros even added one on his own.

He wants to be in his picture and therefore will have to fire his cameras remotely. But Hosefros's desire to be in the shot is not merely ego.

He was born on the Fourth of July, too.

Next week in this space: Stamps and Coins columnist Bill McAllister.