IF IT'S Friday, that must mean a new slide film has been unveiled.

Actually, it only seems as if film makers -- most notably Kodak and Fuji -- have been cranking out new color emulsions every week. Still, there is no denying that the past few years have seen an explosion in the number of slide films available to amateur and pro alike -- to the benefit of us all.

Different slide films see different colors, or the same colors differently, and serious color photographers tailor those differences to the type of work they are doing.

Looking for otherworldly, intense greens? Fujichrome Velvia is for you.

Want golf-ball grain in low light? Push the heck out of a 100-speed film like Ektachrome 100-Plus Professional or go with Fuji's 1600D.

Looking for great skin tones? One of my favorites is Kodak's E-100SW with its built-in warm cast.

See what I mean?

The newest entry into the crowded company of slide films is Fuji's highly touted Provia 100F, a film whose principal claim to fame is incredibly tight grain structure, to rival, if not surpass, that of the legendary Velvia (ISO 50), not to mention those of the hot new Kodak Ektachromes -- 100S, 100SW and 100VS -- the new Provia's closest competitors.

There is no doubt: This is the tightest-grained 35mm color slide film I've seen. I would have to go back to my early days as a photographer -- to when I was using Kodachrome at an ISO of 10 (that's right, 10!) -- to rival the grain in this new film. In terms of grain (but only in terms of grain) this film rivals and probably beats, that old Kodachrome's legendary successor, Kodachrome 64.

What does this mean to the average photographer?

Big prints, that's what.

This is a film that can produce spectacular prints by conventional projection enlargement -- -and who knows what miracles can be had when the image is scanned digitally? Under the right conditions, that can translate into exhibition and salon prints 16 by 20 inches and beyond that will look as if they were shot in medium format, not just piddly little 35mm.

(Important note: In gauging a film's performance, grain is only one criterion. There also is acutance -- a film's ability to produce a sharp edge between two different, adjacent tonal areas -- and resolution -- the ability to resolve fine detail like hairs, eyelashes, etc. The new Fuji film performs admirably on these counts but is off the charts when it comes to grain.)

To give you an idea of how tight the grain is, there I was in my darkroom, performing a decidedly unscientific yet effective test. I compared 35mm frames of the same image, one made on Provia 100F, the other on 100VS Ektachrome. In the dark I placed each image in my enlarger, projected it down onto a white sheet of paper and used my grain focuser to literally focus on the grain in the picture.

Only I couldn't do it with the 100F. There wasn't any.

Now if grain were the only criteria for judging a color film, this review could end here. But, unfortunately for Fuji, there is the little matter of color -- the way the film actually "sees" and renders its subjects. Here, I am bound to say that the new Fuji film falls down when compared to the big three Ektachromes, especially the 100VS, which I previously have dubbed the "Velvia Slayer."

I will concede right off that judging color rendition is subjective. But it is significant, I think, that when I had my test rolls developed by StarLab Photographic Services in Bethesda, owner Ron Fine and staff agreed with me that the 100F was no match for the VS in several key areas. For example, I shot in about half a dozen different places, did a few available light portraits, too. By themselves, the 100F results would have been fine, but compared to the Ektachrome the red on a shiny red convertible had appreciably more snap, the skin tones on my friend Morris were better with the Kodak and -- perhaps most telling -- the rendition of a white brick building against a brilliant blue sky was far more accurate with the VS, lacking the decided yellowish cast of the Provia 100F. (For the record, obviously I used the same lens to test both films.)

Finally, as a longtime critic of Fuji's fictitious, overly optimistic, film speeds, I am happy to report that, unlike its predecessor, Provia 100, Provia 100F does seem to be a real 100-speed film. That is: where in the past I would have to rate Provia at an ISO of 64 to get accurate exposures (just as I would have to rate 50-speed Velvia at 32), this time the 100F lived up to its advertised film speed.

Accurate speed. Excellent grain. Somewhat disappointing color. Two out of three ain't bad; in fact, it's pretty darn good.

Questions or comments? Write me c/o Weekend, The Washington Post, 1150 15th St. NW, Washington, DC 20071 or via e-mail at fvanriper@aol.com