Tuesday, April 16, 2013
When it comes to resolution, for most pros some is good, more is better and too much is just right
Medium-format sensors are CCD units, and they and the onboard processing are optimized for optimum image quality in good light (i.e., low ISO settings). DSLR sensors today are CMOS units, optimized for better performance at higher ISO settings (less light). So low-light specialists will be better off with a full-frame DSLR for the better high-ISO performance. But for ultimate image quality in good light, you can't beat a medium-format sensor, especially those 80-megapixel units. (Phase One's Sensor+ technology "bins" pixels—combines data from four pixels into one—to increase the ISO capability four times, at reduced pixel count: The 80-megapixel IQ180 back has a normal ISO range of 35-800 at 80 megapixels and a range of 140-3200 in Sensor+ mode at 20 megapixels. Medium-format companies are also working on medium-format CMOS sensors, which should provide even better low-light performance (as well as DSLR-like live-view and even video capabilities).
Many medium-format backs can be adapted to a wide range of medium-format cameras—Mamiya, Phase One, Contax, Hasselblad V and H, and even view/technical cameras. Thus, when an exciting new sensor (or camera body) becomes available, you need only upgrade that. With a DSLR, the sensor and body are a unit—if you want to upgrade one, you have to upgrade both (this is also the case with the Leica S/S2 and Pentax 645D cameras; they have built-in sensors, not separate backs).
Most medium-format cameras accept a number of leaf-shutter lenses. Leaf shutters offer the advantages of quiet operation with less "recoil," as well as flash sync at all shutter speeds, even at full flash power (focal-plane-shutter DSLRs have maximum flash-sync shutter speeds of 1⁄300 sec. or slower, and those that offer "high-speed sync" do so at much reduced flash power).
Many newer medium-format digital cameras provide touch-screen operation (only a few DSLRs do, none of them high-end models) for quicker and easier shooting. This, plus versatile tethered operation, and the superb image quality combine to make medium-format digital the ultimate choice for many pro and fine-art photographers.
Doing The Math
|The more pixels an image contains, the larger you can blow it up before the pixels themselves become visible to the eye. Of course, factors like viewing distance come into play—the farther you are from a print when you view it, the less likely you are to see the individual pixels making up the image. Viewed at close range, those giant billboard images aren't very sharp—and they're pretty pixelated.
For the print publishing industry (magazines like this one), you generally want 300 pixels per inch. Thus, simply dividing the image's resolution in pixels by 300 tells you how big you can publish it in inches: an 80-megapixel image from a medium-format camera measures 10328x7760 pixels, meaning you can run it 34.4x25.9 inches at 300 ppi. For a 36.3-megapixel image from a Nikon D800, pixel measurements are 7360x4912 so, dividing those figures by 300, you can run it 24.5x16.4 inches at 300 ppi. Images from 24-megapixel DSLRs measure 6000x4000 pixels, so they can be published at 20x13.3 inches at 300 ppi.
These are measurements of area, of course. Resolution is a linear measurement, so many lines per millimeter or per picture height. An 80-megapixel image contains 2.2X as many pixels as a 36.3-megapixel image, but, all other things being equal, it provides only a 1.4X increase in linear resolution. That's still a goodly increase, but not the more than double you may expect from the more-than-double pixel count. Similarly, going from a 24.3-megapixel DSLR (6000x4000-pixel image) to a 36.3-megapixel DSLR (7360x4912-pixel image) produces just a 1.22X increase in linear resolution (lines per mm or per picture height). But in each case, file sizes increase with the total number of pixels, not the linear resolution: Double the pixel count, and you double the file size—and the space required to store the image and the processing power needed to process it. Note that amount and type of compression (none, lossless, lossy) also will affect file size.
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