The Pentax SMC D FA 645 55mm F2.8 AL (IF) SDM AW ($1,199.95 direct) was the first lens that Pentax released with the 645D digital medium format camera, and with good reason. It’s a standard-angle design, which is an excellent lens for general use, and it’s quite sharp. Like the 645D, it’s weather-sealed, so you can take it out and shoot in rain and shine alike. The $1,200 price tag is a bit on the high side—Mamiya’s similar lens for its digitial medium format system can be found for around $800. But even though the 645D is now priced $1,200 below its original $10,000 asking price, getting into digital medium format photography is not an inexpensive proposition.
The lens itself is fairly squat when you consider the big image sensor it’s designed to cover. Even though the 645D’s 40-megapixel CCD sensor is a bit smaller than a 6 by 4.5cm film frame, this lens produces an image circle that lets you pair with your 645N film camera if you choose to do so. It measures 3.2 by 2.7 inches, weighs about 14.7 ounces, and supports 67mm filters. A reversible lens hood is included. When paired with the 645D its field of view is roughly equal to a 43mm lens—a focal length that Pentax 35mm SLR shooters are familiar with in the form of the legendary SMC FA 43mm f/1.9 Limited lens. If you opt to use it with film, it’s a bit wider, acting more like a 35mm wide-angle lens.
I used Imatest to check and see just how sharp this lens can get, and the results were impressive. Even at f/2.8 it exceeds the 1,800 lines per picture height that we use to classify an image as sharp. At f/2.8 it scores 2,325 lines, which increases a bit as you stop the lens down. Edges are a little softer than the center wide open—but still quite sharp—but you get more even scores by f/5.6, where the average is 2,462 lines. It peaks at f/11, scoring 2,544 lines there. Distortion is a nonissue. You should feel free to shoot the lens at any aperture in order to get your shot, as the image quality throughout its range is excellent.
If you’re interested in the 645D system, the Pentax SMC D FA 645 55mm F2.8 AL (IF) SDM AW is a good lens with which to get started. It’s very sharp, sealed against the elements, and it can be used on film, if that is still part of your workflow. If you already have a stable of 645 lenses from your analog days, you may feel that you can skip it, especially if your work is restricted to the studio. But if you plan on shooting with the 645D outdoors and want to take advantage of its sealed design, pairing it with a similarly sealed lens is a necessity.
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