TECHNOLOGY CENTRAL SHUTTERS SHUTTER AT HIGH SPEED In the age of megapixels and color spaces we often take the basic compo- nents of camera technology for granted. Photographers tend to overlook the ingenuity of the shutter mechanism installed in HC lenses – and yet it is no less of a technical feat than all the other components in the H System. BY HaNNS W. FRIEDRICH At Hasselblad in Gothenburg/Swe- central shutter, on the other hand, PhOTO: RICHARD DawSON den, Tomas Johansson, the developer freezes any movement far more in charge of the central shutter mech- effectively while also completely sup- anism, cranks a test unit, sets it off pressing the influence of the ambient and watches it fire away for minutes light. The photo on the left illustrates at incredible speed. “The H camera the concept: spray water could never might not take 20 pictures per sec- have been frozen as effectively in a ond, but that has nothing to do with well-lit studio with the H3D set to a the shutter,” he remarks with a grin. flash sync speed of 1/125 second. The Swedes are proud of their shut- A focal plane shutter generally ter. It’s one of the H System’s core uses a vertical slit to expose every components and the ‘mechatronical’ pixel or grain line by line, thus cover- device is as simple as it is ingenious. ing the image plane at rapid speed. H System users enjoy its unsurpassed Flash photography requires the first precision and versatility. Laymen will shutter curtain to open entirely ask, what’s the big deal with a shutter before the second can shut the film mechanism that shoots only 1/800 window. It calls for a 1/60, 1/125 or, second at maximum speed? Even at best, 1/250 second shortest flash amateur cameras with focal plane shutters – installed in the camera, as opposed to every lens – are known to SYNOPSIS fire away at 1/8000 second. But, the • The H System’s central lens pros will know. Central shutters have shutter allows for flash photogra- obvious advantages: for example, phy at 1/800 sec – the camera’s flash units can be used throughout fastest shutter speed. In this all shutter speeds – including the area, it outshines the focal plane 1/800 second setting. shutters found in 35mm systems. • The patented ’mechatronical‘ ADVANTAGES OF THE shutter built in Sweden causes CENTRAL SHUTTER almost no vibration, uses a mini- There is, in fact, a whole array of mum amount of movable parts positive assets in the central shut- and consumes very little energy. ter. It allows for approximately three • Super high-tech materials and exposure values more flash sync a sophisticated control board speed than a focal plane shutter. inside every H lens ensure super- This means flash photography with lative operation. almost entirely suppressed ambient • The shutter is very precise light, providing the photographer and reliable. Its lifespan extends with absolute control over his light- far beyond 100.000 exposures. ing. What starts out being beneficial • Hasselblad’s True Exposure in the studio proves to be downright mode guarantees correct indispensable in some flash scenar- exposures independently of the ios outdoors. aperture setting. Richard Dawson took this Where the exposure is longer and picture for GQ magazine using subjects are moving, available light a Hasselblad H3D-39 with may lead to an unsharp secondary the flash set to 1/800 to virtually exposure whith blurry contours. The freeze the spray water significantly faster sync speeds of a 2/2008 33 24470_UK_VIC_0208_3235_T_Shutter33 33 25.04.2008 6:40:39 Uhr TECHNOLOGY CENTRAL SHUTTERS hair. The construction is designed think. Counter impulses – generated to cause minimal abrasion and work by magnetic fields – prevent the seamlessly. blades from bouncing back (and forth!) after opening or closing. The TWO VERSIONS OF 20 fastest internal speeds, from 1/250 THE SHUTTER to 1/800 seconds, are each controlled by a reference table, listing the con- Hasselblad builds the shutter in two ditions, length and strength of the sizes: one measures 20 millimeters electro-magnetic impulses. The in diameter, the other 28. The large tables are installed in the shutter’s version is used for high-speed and control board and become increas- tele lenses. The larger the shutter, the ingly sophisticated at faster speeds. more difficult to build. For instance Designers went to great lengths to the blades of the 20 mm version weigh puzzle out these lists with sophisti- 0.13 grams and the shutter spring cated measuring tools and high-speed develops a force of about 7 Newton, cameras. The extreme precision they the equivalent of 700 grams. The obtain is then made real when every large 28 mm shutter, in turn, requires shutter is gauged and calibrated indi- two motors to move the 0.22 gram vidually in the factory. The H shutter comes in two types: shutter blades with a speed equal to 2 The electronic control mechanism the smaller 20 mm version (left) that of the smaller model. At 35 N warrants exposure speeds with supe- has one motor; the larger, more and 3.5 kg, the springs call for five rior accuracy. It’s highly beneficial sophisticated 28 mm shutter uses times the tractive force, making the in specialized fields like aerial pho- two motors for compatibility with 28 mm version far bigger and more tography where it guarantees 100 telephoto and high-speed lenses sophisticated. An even larger mecha- percent synchronized exposures nism for even bigger and faster lenses using various lenses. It also enables could no longer be manufactured True Exposure. Here, an electronic under reliable, economic conditions control considers that the shutter sync speed – all depending on the known to use both central shutters camera system and type of shutter. and focal plane shutters. The general Exposures take as long as the flash inclination, though, has always been sync speed, or longer: i.e., even if toward the central shutter. Users the shutter speed is set at 1/2000, prefer advanced flash compatibility it might still take 1/125 second for to lighting-fast shutter speed. The the shutter to perform. Any move- ‘mechatronical’ central shutter was ment during this time – whether by in fact built before the H camera, as the camera or the subject – can lead the H1 requires lenses with absolutely to visible distortion as is frequently precise, electronically controllable seen in sports images. The central internal shutters. The mechanical shutter, on the other hand, will have levers in the lens bayonet are thus nothing to do with this ‘rolling shut- made redundant. The central shutter is installed effects from opening the shutter the middle. The light-weight, ter’ effect. It sits in the optical center inside the lens, back to back with from the middle to the outer sides, high-speed blades guarantee pre- of the lens right behind the aperture. THE HAssELBLAD the aperture. There are no side first leaving the light through in cise exposure speed at 1/800 sec For this reason, it makes no differ- CENTRAL SHUTTER ence that the central shutter cannot open or close with infinite speed. It 1 The basic principle behind the opens first in the middle and closes shutter control system, conceptual- last in the middle: the fast, aperture- ized and patented in Sweden, is as the moving system. This is a clever – especially not if it is to perform at – which opens in a circular fashion like opening and closing mechanism simple as it is ingenious: a mecha- idea that boasts a number of advan- 1/800 second. However, we would from center to edges – clears a small has no optical repercussions and nism transfers the angular movement tages: for one, the shutter will remain expect no less from the H lenses. aperture faster than a wide-open one. doesn’t lead to vignetting. of a lever onto the shutter blades. open or closed without using any Speeds of 1/500 second and slower Since the introduction of the H1, the An added bonus of the central The core piece, a powerful, M-shaped energy whatsoever. Both states are use, almost exclusively, the force photographer no longer has to cor- shutter is that it causes virtually no spring, would normally keep the stable and autonomous. of the spring to open and close the rect the exposure – something even vibration. The forces applied by the lever locked in the center position. As a whole, it’s a motor-less shutter shutter. The lever moves in tandem most experienced photographers tiny, ring-shaped shutter blades are It is attached to an anchor held by solution that uses very little energy. with the speed of the powerful coil as would overlook – when the aperture neutralized almost entirely. The two two fixed neodymium magnets on With the majority of shutter speeds, it springs freely. The magnetic field is small. curtains of the focal plane shutter, by both sides, i.e., in the open or closed the magnetic-field-enhanced ‘push’ will compensate for any mechanical 3 Hasselblad makes no compro- comparison, spring off in the same state. When the anchor touches one described above is only really needed abrasion using a nominal amount of mises when it comes to the accuracy direction only to hit resistance and of the magnets, the magnetic circuit to help compensate the nominal fric- energy. Faster speeds, on the other of the shutter. Internally, the Swedes cause camera shake. Normally, any is closed and a large holding force is tion caused by the shutter. The spring hand, call for more acceleration.