The lines between top-tier and mid-level camera models are blurring. We look at the features and capabilities that are most important for your work so you can make a thoughtful decision before leaping into an über-pro hot-rod unit.
And on the subject of formats, if you expose at the same shutter speed and ƒ-stop in the same light, a larger sensor's greater area can collect more photons, and that results in a better photonic signal-to-noise ratio. So, the larger the sensor, the better (assuming equal technology). However, the larger sensor will produce less depth of field at the same settings when using a lens focal length that provides the same framing at a given shooting distance (and, thus, the same perspective). If you want the same depth of field with the larger sensor, you must stop the lens down and either use a longer exposure time to compensate (which could produce blurring with moving subjects or handheld shooting) or use a higher ISO setting to permit shooting at the same shutter speed at the smaller aperture (which results in less light—fewer photons—striking the sensor, largely negating the larger sensor's noise advantage). Or you just could accept the reduced depth of field, and shoot at the same shutter speed and aperture—for some purposes (selective focus, video), less depth of field is actually a good thing.
Today's full-frame CMOS sensors tend to have more advanced technology than medium-format CCD sensors, in a number of ways, offsetting the medium-format CCD's great size advantage. Medium-format scored well in bit-depth at DxOMark.com, taking the top two places, but faired less well in dynamic range (the top medium-format sensor trailed seven full-frame DSLRs and four APS-C models). In high-ISO performance, it's all DSLRs: Full-frame models took the top 19 spots, trailed by an APS-H, then two medium-format models, then five APS-C models. If you're looking for a new camera body, check out www.dxomark.com; while there are other important considerations like resolution, AF performance, shooting speed, durability, etc., DxO should be one stop in your research.
If fine details with stationary subjects in good light are your priority, you can't beat medium-format: 80 megapixels trumps 36.3. But 36.3 megapixels provides a lot of detail; only extreme requirements would find that wanting, and 16 to 24 megapixels are ideal for many pro needs. Also, huge-megapixel images take up lots of space on memory cards, and take time to process—those big medium-format cameras rarely shoot more than one frame per second. If dynamic range is your priority, bearing in mind that practical photographic dynamic range will be somewhat less than DxOMark's figures, the top cameras of all three formats perform well with all sensor sizes. If low light and high ISO are priorities, you can't beat full-frame DSLRs.
Four Thirds System
While it has taken a back seat to the mirrorless Micro Four Thirds System (which uses the same 17.3x13.0mm sensor size) in recent years, the original Four Thirds System is still around in the form of the Olympus E-5, a true pro DSLR, rugged and splashproof, with a complete lineup of lenses, many of which are also weather-sealed. (The original Four Thirds System camera also was a pro model, the Olympus E-1.)
The idea behind the Four Thirds System was to provide lenses designed specifically for digital imaging with a specific sensor size. Other manufacturers essentially adapted their 35mm SLR systems for digital, more recently designing lenses specifically for digital imaging and sensor sizes. By using the smaller 17.3x13.0mm Four Thirds sensor format, the hope was to keep system size down.
Larger-format cameras also have come down in size—the Olympus E-5 is about the size of the Canon EOS 6D, Nikon D600 and Sony SLT-A99 full-frame DSLRs—and it took the mirrorless Micro Four Thirds System to truly realize the size benefits of the smaller sensor. But the E-5 remains a solid pro performer, with quality lenses from a 7-14mm and an 8mm fisheye to a 300mm, providing users with 35mm-camera-equivalent focal lengths of 14-600mm thanks to the sensor's 2X crop factor.
Notable E-5 pro features include superquick AF, a tilting/rotating, 3.0-inch, 921K-dot LCD monitor, a 100% viewfinder, slots for CF and SD media, multiple aspect ratios and multiple-exposure capability.