BetterPhoto Q&A
Category: Traditional Film Photography

Film speed

Thank you

Marie

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June 18, 2002

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June 20, 2002

Marie

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June 20, 2002

Resolving power of film varies. In general, the slower the speed, the higher the resolution. This is particularly true in families of films, such as Kodak Gold 100 compared to Gold 200 or Gold 400 (now Gold Max). However, Kodak's Portra 400NC, Portra 400VC, and Supra 400, all professional films, have a significantly better print grain index (PGI) than Kodak Gold 100! So does the "high end" consumer film, Royal Gold 400. Gold 100 (now called "Bright Sun Film") is very nearly as grainy as the Portra 800 and Supra 800. PGI is Kodak's wacky "graininess" comparison system for color negative film that nobody else uses.

Conclusion:
You cannot assume that slower speed is less grainy between families of films, even from the same manufacturer. You need to read the data sheet for each film you're considering using.

For films other than Kodak's color negatives (including Kodak's B/W and slide films), the diffuse rms granularity figure and MTF curve show how fine grained the film is and what to expect in apparent sharpness. Particularly applicable to "apparent sharpness" as perceived by the human eye is the MTF curve. However, it's not the far end of the curve that's important. For apparent sharpness as perceived by the human eye, it's how high the curve is for the "middle" numbers from about 20 to 60 line pairs per millimeter. The higher the curve through this region, the more a human will perceive it as having greater sharpness!

-- John

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June 21, 2002