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

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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. adhere to far stricter standards potential shutter vibration cannot created that keeps the shutter open inside the shutter mechanism is what Ultimately, it is the capacity of the than what is dictated by the ISO be compared with the more violent or closed more dependably. ensures that the blades are fired open shutter blades that constrain the for medium-format cameras. The flap sound of the mirror inside SLR However, the moment the con- at high speed and then brought to a speed. Extreme acceleration could amount of fine-tuning invested by cameras. However, since the H3D nection is cut, the spring yanks the gentle halt on the other side, ensur- simply cause the laminate to dissolve. Hasselblad engineers, combined will optionally open the mirror long lever back to the opposite side where ing that they do not collide with the The 1/800, however, guarantees long with the superior electronic con- before the shutter fires, the smooth it is held by the other magnet. To stop position at full speed. No, the life – even though it already is subject trol options, ensures that all shutter central shutter of H lenses has indis- cut the connection on either side, a four shutter blades are handled with to unimaginable forces which only speeds remain within the tightest of putable advantages. magnetic field is generated to neu- care for they consist of carbon fiber carbon fibers can withstand. tolerance margins – barely one-tenth Over the years, medium-format tralize the magnetic power and also, laminate and measure 0.08 millime- The shutter control mechanism of an exposure value – even though cameras by Hasselblad have been for short exposure times, add force to ters – about the width of a human is far more complex than one would the company’s internal norm would

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24470_UK_VIC_0208_3235_T_Shutter34 34 25.04.2008 6:40:52 Uhr Central ShutterS – At a glance allow as much as three-tenths, and to a flash unit, they gather the energy the ISO even four-tenths discrep- to generate the magnetic field. In the ancy. In theory, the ISO tolerance 28 mm shutter, the exposure unit is 1 This is how the patented Hasselblad central shutter works norm stocks enough reserves to comparatively large and it is difficult The shutter system is based on a lever attached to a transform the standard 1/800 into a to incorporate into the construction. moving anchor. The movement of the lever is transferred prestigious 1/1000 second. Mechani- However, the optical department onto the shutter blades, while the M-shaped spring cally, nothing would even have to are happy to work with the two, dif- tries to pull the lever to the centre position. On both change. However, this would go ferently sized shutters. The smaller ends, the anchor is held by fixed magnets. The combined against the Hasselblad philosophy. version slots right in without a fuss, force of the magnets is slightly stronger than the force As it is, the HC lens simply ensures while the larger gives birth to high- of the spring, ensuring that the shutter is automatically exact exposure speed while keeping speed lenses such as the HC 100mm held in either the open or the closed position. To open the shutter, a magnetic field is generated with the help sufficient tolerance levels for backup. f/2.2. Here, the depth of field at of coils, cancelling the retention force. For fast shutter And it proves to be very reliable and open aperture is spectacularly low, speeds the coils also add driving force to make the accurate in the field, where consecu- while the speed leaves little room for anchor move faster. In other cases, all that’s needed tive exposures all stay precise within improvement. is a miniscule electric signal 0.02 exposure values. HC lenses are assembled at their partner company Fujinon. The expo- Live Span Beyond sure unit itself, being the complex 100,000 Exposures and highly critical component for the correct functioning of the lens, Shutter designer Tomas Johansson is made in Gothenburg and sent to hasn’t given up his dream of a ‘real’ Japan as a complete unit. All parts are 1/1000 second. “All it should take is assembled with extreme care; physi- a bit of extra fine-tuning and modi- cal dimensions have to be correct fying. The 1/1000 is on my agenda,” and the control lever attached to the 2 True Exposure he says. However, the speed issue blades with utmost precision. The is rarely even raised by users. There tolerance margins for the various Measured shutter speed Measured shutter speed appear to be plenty of other areas that components are abysmal while the at full aperture stopped down can be improved first – but the shut- demands on the material very high. ter mechanism keeps evolving. The workers involved in assembly all The 1/800 second, on the other possess exceptional dexterity as tasks hand, gives the shutter a markedly can be rather finicky. The blades are Time Time Film plane lightlevel Film long life span. The exact number of mounted using a critical, tiny drop lightlevel plane Film exposures is rather open, though it of grease; not enough would result is always likely to extend beyond in premature wear and tear; too 100,000 shots. Johansson points much oil could end up on the lens. The shutter is similar to the aperture diaphragms in integral component of the camera system, designed to toward a shutter that had fired more The aperture and shutter are meticu- centre of the lens and opens and closes in a similar way. compensate for deviations. In shorter exposures, the than 250,000 exposures. Afterwards lously checked and calibrated before However, despite all efforts, the speed of the blades timing for the opening and closing of the shutter is it continued to perform within the leaving as a finished component on remains limited. If the aperture is small, the light open- adapted so that the exposure speed is exact and inde- acceptable tolerance margins and, the long journey to Japan only to ing is cleared a little earlier and closed a little later than pendent of the aperture setting. Extremely fast in addition, displayed no wear and then return to Sweden as the heart when the aperture is wide open. With the introduction exposures are compensated for with a marginal adjust- tear as it was being disassembled. piece of an HC lens. of the H1, Hasselblad’s True Exposure has become an ment to the aperture, in order to keep the generated exposure independent of aperture setting. Only the fast- Since the burden of exposures is est shutter speed combined with the smallest aperture distributed across all H lenses, the Conclusion setting could result in slightly flawed exposures, but for- contingency risk to the shutter is tunately this is a combination that rarely occurs minimal and occurs only rarely. The Those who believe the shutter to be engineers will then inspect the cause a simple component wherin a few of the defect and use their insights to blades open and close, can remain 3 Electronic control for greater accuracy make improvements. true to their conviction. In a sense, The shutter and the aperture are they are right: the central shutter is Exposure tolerances Hasselblad/ISO mounted back to back. They form as reliable as it is frugal, does exactly Thanks to the mechanical design and elec- 0,50 the exposure unit, the heart of every what is expected of it and asks noth- tronic control system, Hasselblad’s centralized 0,40 HC lens. Hasselblad manufactures ing more of the photographer than shutters are extremely accurate in perfor- both the aperture and the shutter in to press the exposure button. The fact mance. The ISO norm (outer curve) would, at 0,30 Gothenburg. Mechanically, the aper- that, internally, a number of inge- a shutter speed of 1/125 second, even allow 0,20 for an 0.4 aperture stop deviation up or down. ture is kept simpler than the shutter. nious controls and magnetic fields 0,10 Hasselblad themselves only allow a tolerance The developers decided to build the are employed to combat mechanical 1/125 1/250 1/500 1/800 of 0.3 values, and then only with speeds 0,00 new version to greater precision vibration and automatically correct upwards of 1/250 second. The listed values -0,10 than the previous unit, which had the shutter speed in relation to the stem from the shutter of an HC 80mm f/2.8.

been supplied by a third party. The set aperture, that the materials can be As we 0,50can see, any deviations remain under ( E V) error E xposure -0,20 0.1 aperture0,40 values and are thus irrelevant in superior shape is obvious. “When pushed to the absolute limit and that -0,30 something requires re-modification many clever minds needed many practice.0,30 If Hasselblad were to transform -0,40 we always make sure we do it the clever ideas and attempts until every- 1/800 second0,20 into 1/1000 second, the lenses would0,10 still perform within the ISO norm, but -0,50 Hasselblad way,” Johansson says. thing finally works, doesn’t have to 1/125 1/250 1/500 1/800 it wouldn’t be an honest solution Shutter speed In addition to the mechanical concern the Hasselblad photogra- 0,00 Hasselblad maximal -0,10 components, the exposure unit has a pher. He can concentrate on taking Hasselblad minimal -0,20 circuit board that is also used for the pictures and simply rely on his gear. ISO maximal -0,30 autofocus motor. What immediately ISO minimal -0,40 stands out on the electronic control For further information please visit 20 mm Shutter, typical -0,50 board are the large capacitors. Similar www.hasselblad.com

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