A normal lens is a normal lens is a normal lens… except when it’s not. When using film, the size of the film determines what a normal, long, and wide lens are. An 80mm lens is long when using 35mm film, normal when using 120 film, and short when using 4×5 film. Using a digital back is no different. A P45+ or P25+ is roughly 3mm smaller on each side than 645 film.But if you’re used to 35mm or large format, then you may have a hard time adjusting. This calculator is designed for people who know one lens system really well (e.g. large format lenses for 4×5 film), and want a quick way to find out what the equivalent lens is when using a Phase One digital back. Simply enter a number into the blue under the system you know, and all equivalent lens for each system will appear in the yellow.

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