Thursday, May 31, 2007
Is There A Medium-Format Digital In Your Future?
When it comes to ultimate digital image quality, nothing beats medium-format cameras and digital backs. The word 'medium' might be tepid—the image quality is anything but.
Larger pixels, or photosites, increase the signal-to-noise ratio and ulti-mately, the sensor's dynamic range, which correlates to better shadow and highlight detail in a photograph. When engineers harnessed the higher dynamic range of a large pixel and combined it with a greater number of those pixels, photographers could make virtually lossless enlargements at huge print sizes. Medium-format digital capture was born.
The current standard in medium-format sensors is a CCD that approximates the 645 film format (50.7x39mm). Its increased information-gathering ability over small-frame sensors is no different than that same ability when comparing medium-format and 35mm films. The difference is that unlike self-contained D-SLRs, medium-format sensors are also integrated via digital backs into existing film cameras.
To meld a digital sensor with a film camera, it has to work around the film-based mechanics. Because the sensor itself is packaged within a ceramic structure that protects the sensor and contains support electronics, a truly 645-sized sensor would be packaged too large to fit within the film rails of a 645 film camera. Thus, the package is designed for 645, and the sensor itself shrinks accordingly to fit within the package.
In the case of Kodak's 39-megapixel KAF-39000 sensor, found in Phase One P45 and Hasselblad H3D-39 and CF-39 backs, the slightly smaller-than-645 size translates to a magnification factor of approximately 1.1x. Compensating for this isn't too much to ask, particularly for photographers used to 1.5x or greater magnification that often comes with D-SLRs.
Manufacturing larger sensors brings additional challenges. Because a typical wafer of raw silicon measures about eight inches in diameter, the change from a small-format sensor to 645 means that instead of one wafer producing dozens of sensors, only a handful can be extracted. Since damage on any part of the chip makes it useless, the manufacturing process is exponentially more difficult and expensive.
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