Large-format view cameras have been a mainstay of high-end landscape photography for a century. Photographers like Edward Weston, Ansel Adams, Eliot Porter and others used large-format view and field cameras, in part, for the image quality their large-format films delivered, and, in part, for their movements, which could correct converging lines, increase depth of field and add emphasis to foreground elements by slightly distorting them.
Today's ultimate image quality in digital terms comes via medium-format digital cameras and backs. Just as the larger "full-frame" image sensors can yield better image quality than APS-C and smaller formats, medium-format cameras surpass full-frame with their even larger sensors and greater resolutions. The trade-offs, besides cost, have been that medium-format cameras are much slower than DSLRs and their CCD sensors don't do high ISO and Live View well. Now, however, new cameras based on the first medium-format CMOS sensor—a new 44x33mm, 50-megapixel unit from Sony—are coming online, and for landscape photographers, in particular, they're worth a careful look. The cameras are the Hasselblad H5D-50c, Pentax 645Z and Phase One IQ250 (the Phase One is a back that mounts to fit several popular medium-format cameras, including Phase One's 645DF+). We'll look at them shortly.
Why Bigger Is Better
In film, bigger is better because you don't have to blow up a big negative as much to produce a given size print. To make an 8x10-inch print from a 4x5-inch negative, you're just blowing the image up 2x linearly, or 4x in area. To make an 8x10 print from a 1x1.5-inch 35mm negative, you're blowing up the image 8x linearly and 53x in area. While 4x5 TRI-X and 35mm TRI-X are slightly different emulsions, the grain is about the same size, and blowing it up 53x makes for a grainier print than blowing it up 4x. And, of course, with 53x as many grains covering the image, detail is far better with the larger format. And this doesn't even take into consideration difference in aspect ratio. While a 4x5 negative fits an 8x10 print perfectly, you have to crop off some of the long dimension of a 3:2 aspect-ratio 35mm image to fill the paper in an 8x10 print, so the difference is even greater.
With digital, larger sensors can hold more pixels of a given size for more detailed images, and larger sensors can collect more light, which improves signal-to-noise ratio for cleaner images.
Photonic noise, the main noise source in most images, varies as the square root of the photon count. If a sensor collects 100 photons, there are 10 photons of noise, a 10:1 signal-to-noise ratio. If the sensor collects 10,000 photons, there are 100 photons of noise, for a 100:1 photonic S/N ratio.
If you put two trays—a one-inch square and a two-inch square—out in the rain for a given amount of time, each will collect the same height of water, say, one inch. But the larger container will contain more water—in our example, four cubic inches versus one cubic inch. Just as larger trays collect more water than smaller ones when left out in the rain for a given amount of time, larger sensors collect more photons than smaller ones when given the same exposure (say, 1⁄250 sec. at ƒ/8).
However, a given ƒ-stop, ƒ/8 in our example, produces less depth of field with a larger sensor when producing the same field of view and perspective. If we want the same depth of field in a photo taken with a full-frame camera as a Micro Four Thirds camera with a sensor about one-quarter area, we'll have to stop down the full-frame camera's lens two stops to ƒ/16, in our example. Doing so requires using a longer exposure time if we want the same image brightness, and that could result in blur in images of moving subjects or handheld shots. This isn't a problem in landscape photos made with a solid tripod and good technique, but it's a consideration for action like birds in flight. Or, we could shoot at 1⁄250 sec. at ƒ/16 and raise the ISO two stops to brighten the underexposed image, but this would result in a noisier image due to less light on the sensor (lower photonic signal-to-noise ratio).
Note that the new 50-megapixel CMOS sensor measures 44x33mm, which is actually not quite "medium format" (that would be more like 53.9x40.4mm). The 44x33mm sensor is 1.68x the size of a "full-frame" DSLR sensor (which, in turn, is 2.36x the size of an APS-C sensor).
Hasselblad was the first to announce a CMOS medium-format camera, although Phase One beat them to the market by a couple of months. The H5D-50c features the 44x33mm 50-megapixel CMOS sensor, 16-bit losslessly compressed 3FR RAW files with a dynamic range of 14 stops, storage on CompactFlash UDMA7 cards or tethered computer hard drive and shooting up to 1.5 fps. You can choose among eye-level and waist-level finders, or use the 3.0-inch 460K-dot LCD monitor. Single-point AF functions down to EV 1, and Hasselblad's True Focus corrects for focus-and-recompose situations. Shutter speeds range from 12 minutes to 1⁄800 sec. (with flash sync at all speeds). Dimensions are 5.3x5.2x8.1 inches and five pounds with 80mm lens and battery. Hasselblad offers 12 leaf-shutter lenses from 24mm to 300mm (equivalent in framing to about 19mm through 237mm on a full-frame DSLR), plus the HTS 1.5 tilt-shift adapter, which provides view camera-like movements with lenses from 24mm to 100mm. There are also extension tubes for close-ups and a teleconverter. List Price: $27,500.
Given equivalent technology, larger pixels can collect light more efficiently than smaller ones. But a given sensor area will hold more smaller pixels than larger ones so, overall, the total amount of light collected is almost the same for a given-size sensor, regardless of pixel size—144 one-inch-square trays will collect the same amount of water as one 12x12-inch tray: 144 cubic inches. So, in terms of noise, which is largely a function of the amount of light collected, sensor area is more important than pixel size/count. In the DxOMark.com Low-Light ISO ratings, the top 27 cameras have full-frame sensors; the top APS-C model ranks 28th, the top Micro Four Thirds model, 72nd. (DxOMark.com hasn't tested the new medium-format CMOS sensor as of this writing.) The top six cameras are full-frame models of 12, 16, 12, 16, 24 and 36 megapixels, respectively (there's only about a 1⁄3-stop difference from first to sixth); and the highest-ranking APS-C model is 24 megapixels, the highest pixel count available in APS-C at this writing.
Also bear in mind that more pixels can deliver more resolution. An 80-megapixel image can reproduce finer detail than a 20-megapixel one because it has 4x the sampling rate. This means better detail in landscapes and wildlife portraits. And, if noise is a concern, downsampling the 80-megapixel image to 20 megapixels actually improves the signal-to-noise ratio. Phase One's Sensor+ technology takes advantage of this by binning—combining data from four pixels into one—to turn their 80-megapixel IQ280 back into a 20-megapixel back that can deliver ISO performance 4x better than it can at full resolution (i.e., ISO 1600 in 20-megapixel Sensor+ mode has the same noise as ISO 400 in normal 80-megapixel mode).
Additionally, some sensors are tuned for high-ISO performance (the Sony a7S, Nikon D4S and Nikon Dƒ, for example), while others are designed for maximum performance in good light/low ISO (the Sony a7R and Nikon D810, for example). Medium-format CCD sensors have been geared for superb low-ISO image quality, but the new CMOS sensor should deliver much improved higher-ISO performance, as well. As mentioned, DxOMark.com hasn't tested the 50-megapixel medium-format CMOS sensors yet, but we expect them to score higher than the CCD sensors, certainly in low-light ISO and dynamic range, if not color bit-depth.
|CMOS Gives Rise To A New Generation Of Medium-Format Cameras
As mentioned above, until very recently, medium-format digital cameras and backs used CCD sensors, while full-frame and smaller DSLRs and interchangeable-lens mirrorless cameras used CMOS. When digital started going mainstream more than a decade ago, CCD offered advantages over CMOS. Today, CMOS offers far better high ISO/low-light capability, better dynamic range and better Live View capabilities—many medium-format cameras don't even offer Live View on the LCD monitor.
Within the last year, three medium-format cameras, each built around a 50-megapixel Sony CMOS sensor that measures 44x33mm, have become available. These cameras are bringing DSLR-like shooting to medium format. Note that while each uses the same basic sensor, each camera manufacturer has its own processing algorithms, Bayer filter array and other tuning that gives each camera its own look.
Besides being far and away the lowest priced at $8,499, Pentax's 645Z offers the most DSLR-like experience of the new 50-megapixel CMOS trio, with a 27-point phase-detection AF system that works in light as dim as EV -3 (ISO 100) and can keep up with the camera's very quick (for medium-format) 3 fps drive rate, shutter speeds from 30 to 1⁄4000 sec., an ISO range of 100-204,800, a tilting 3.2-inch, 1037K-dot LCD monitor, and a weather-sealed and cold-proof body. It's also the only medium-format digital camera that can shoot HD video—1080 at 60i and 30p. There are two slots for SD/SDHC/SDXC cards, Eye-Fi cards and Flucards (which add the ability to control the camera wirelessly via a smart device). You can choose from two 14-bit RAW formats, Pentax's own PEF or Adobe's "universal" DNG. As with all medium-format digital cameras, there's no AA filter on the image sensor. The D-LI90 lithium battery (the same one used in the K-3 DSLR) is good for 650 shots (per CIPA standard). Dimensions are 6.1x4.6x4.8 inches and 3.2 pounds (body only). The 645Z accepts Pentax 645 lenses from 25mm to 400mm (and Pentax 67 lenses, via adapter), but performs best with the new 645AF2-mount lenses, which currently number two (D FA 645 55mm ƒ/2.8 SDM AW and D FA 645 90mm ƒ/2.8 Macro AW SR). Maximum flash-sync shutter speed is 1⁄160 sec.; there are no leaf-shutter lenses.
| Greater Care Required
To get the most out of medium format, it's imperative that you do everything possible to eliminate sources of image blurring. This means using a solid tripod, focusing carefully (manually, using Live View, if available), using a cable release to avoid jiggling the camera as you depress the shutter button and using mirror lock to let vibrations settle down before making the exposure.
Phase One IQ250
Phase One's IQ250 is actually a back, not a camera (although Phase One will be happy to sell you one in a kit with a Phase One 645DF+ camera body). The back is available in mounts for a number of popular medium-format cameras (including tech cameras, although with some lenses, the sensor's microlenses can cause problems when using the movements). The $34,990 back provides ISO settings from 100-6400, Live View on the 3.2-inch, 1150K-dot touch-screen LCD monitor (or on tethered computer via Phase One Capture Pilot), 14 stops of dynamic range, exposure times from one hour to 1⁄10,000 sec., and rugged construction from aircraft-quality aluminum. The IQ250 can shoot at 1.2 fps and has a big 2 GB image buffer to keep the images flowing.
The 645DF+ body accepts a wide range of Phase One Digital focal-plane lenses and Schneider Kreuznach leaf-shutter lenses, plus Mamiya AFD lenses, and is compatible with Hasselblad V lenses. Flash sync goes as high as 1⁄1600 sec. with leaf-shutter lenses.