Basics: Shutters, Shutter Speeds and Exposure

A camera shutter regulates the length of time for which the film or image sensor is exposed to the light: no more, no less. There have been endless designs of shutter, beginning with the photographer's hat or (later) a lens cap: the photographer uncovered the lens, then covered it again. In the 1920s it was apparently quite common, when photographing the interiors of churches, for the photographer to go next door to the pub for lunch during the exposure. Today, more and more cameras offer 1/4000 second or faster, though the number of occasions when most photographers need even 1/1000 second is limited.

exakta & wine

Exakta, wine, torch

Even Roger, who took this picture, can never quite decide whether he likes it. But what success it has, is due to careful exposure. Any more exposure (this was shot with a Nikon D70 digital SLR and Dreamagon soft focus lens) and it loses the moody, lost-in-the-past effect and becomes too literal. The actual exposure time was about 1/5 second; modern digital SLRs allow you to set intermediate speeds between the traditional values (see below).

 

Basically, just two designs of shutter remain popular for serious cameras. One is the reciprocating or leaf shutter, where thin metal blades whip open; stay open for a fraction of a second; then whip closed again. These are normally built into the lens, though on a few cameras they are behind the lens.

Leaf shutter

This is a basic three-bladed shutter; fancier examples normally have 5 blades. The black ring 1 engages with each leaf via the slot 2. When it rotates, the leaves rotate about the pivot 3. Only one leaf has been labelled, for simplicity.

 

leaf shutter

 

 

slit shutter

 

 

The other type of shutter is the travelling slit, where the shutter consists of two curtains going in the same direction, and the exposure time is governed by the width of the gap between them. It is also governed by the speed of movement of the curtains, and on some older shutters, this could be varied, but nowadays it is usually fixed. The shutter is normally just in front of the film (a 'focal plane' shutter) but long ago, in the days of brass lenses, there were travelling-slit shutters that were mounted in front of the lens.

 

Focal plane shutter

As its name suggests, this is just in front of the focal plane. Again, this is a really simple, schematic diagram. Usually the two curtains are independent so that the slit-width can be varied, and so that the shutter does not admit light when it is being re-cocked, i.e. it is 'self capping'. Some very old cameras do however have several slits of different widths on the same blind.

Most modern shutters offer a 'core' range of speeds from 1 second to 1/500 second (leaf shutters) or 1 to 1/1000 or 1/2000 (focal plane shutters). The sequence more-or-less halves (or doubles) with each step: the discrepancies, such as 1/15 instead of 1/16 (half of 1/8) or 1/125 instead of 1/120 (half of 1/60) are not worth worrying about.

The '1/' is normally omitted on the speed dial or setting ring (see below) and therefore runs 1 - 2 - 4 - 8 - 15 - 30 - 60 - 125 - 250 - 500 - 1000. This may be extended to a range of whole seconds, which normally have 's' after them, thus 16s - 8s - 4s - 2s - 1 - 2 etc, and with many modern cameras with travelling slit shutters the sequence is extended in the other direction, this (1/)1000 - 2000 - 4000 - 8000.

 

 

Shutter on Nikon EM SLR

This is a modern, vertical-run 'collapsing blade' moving-slit shutter; older versions often ran side to side across the long dimension of the film (as in the diagram above) and were usually made of cloth, though flexible stainless steel and titanium foil have also been used.

 

focal plame EM

 

 

footballers, goa

 

Footballers, Goa

Fast shutter speeds to 'freeze' action aren't always the best idea. The ball is pretty much 'frozen' here, but the overall mood is very static. Some players are not moving at all, and with others, you can't really tell. Instead of the 1/250 second (at f/5.6) that Roger used here, a shutter speed of 1/30 second (at f/16) might have produced a more interesting, dynamic picture. Leica M4-P, 35/1.4 Summilux, Fuji RFP ISO 50.

Old shutters

Many older cameras use a less linear sequence of 1 - 2 - 5 - 10 - 25 - 50 - 100 - 200 (or 250 or 300) - 500. Allowing for old age and the fact that camera shutters rarely get faster as they get older, you can safely treat 1/5 as 1/4 and 1/10 as 1/8, and 1/25 to 1/100 as 1/3 stop slower than 1/30, 1/60 and 1/125, i.e. open up the lens by 1/3 stop (see the free basics module on lenses).

Easier still, just treat them as the next speed down: 1/15 for 1/25, 1/30 for 1/50 and 1/60 for 1/100, etc. If you are shooting negative film, the exposures will be quite accurate enough. If you want to shoot slides, you will have to do a bit of testing for yourself.

 

compound dagor

 

 

 

Compound shutter

We thought you might be interested to see how shutters used to be. This probably dates from around the time of World War 1 and uses the old sequence mentioned above, 1 - 2 - 5 - 10 - 25 - 50 - 100 - 200. It is a 'leaf' or 'between-lens' shutter, where the shutter itself is between the elements of the lens.

Speeds are set on the dial at the top; the shutter is cocked via the lever on the right; and the little knob below the lens must be set to 'I' (instantaneous) for timed speeds; 'B' (Bulb' or 'Brief'), which keeps the shutter open as long as the lever (top right) or cable release is depressed; or 'T' ('Time', sometimes 'Z' for 'Zeit') where the shutter opens on one pressure and closes on a second pressure. It doesn't need to be cocked for 'B' or 'T' but it must be cocked for 'I'. Modern cameras and shutters are a lot easier....To make life more interesting, Compound shutters (which are fantastically reliable) are pneumatically governed, by the rate air goes through a valve (a piston moves in the tube on the top behind the dial).

 

Setting the shutter

As the Compound shutter above shows, the shutter speed setting dial can be almost anywhere, so the easiest thing to do is to look for a shutter speed sequence written somewhere, and see how it can be varied. With modern electronic cameras that tell you the shutter speed on an LCD read-out, you're on your own: get hold of the instruction book.

 

nikon dial

Nikon F shutter speed dial

Set to 1/60 second, the maximum speed at which electronic flash will synchronize. The index mark (not visible here) is on the camera body. 'Focal plane' shutters (just in front of the film) do not synchronize at the higher shutter speeds.

 

nikkormat dial

Nikkormat shutter speed dial

Set to 1/15 second. The higher speeds (in red) cannot be used with electronic flash; there is not much consistency in how such things are marked. If you use one of the red speeds, the shutter will not be fully open when the flash fires, and part of the frame will not be exposed. Another focal plane shutter.

 

samoca lens detail

Samoca shutter speed dial

Set to 1/25 second; the Samoca has the old shutter-speed sequence, described above, of 1 to 1/300 second. This arrangement, with a ring around the lens, is typical of between-lens (leaf) shutters, which synchronize with flash at all speeds.

 

Olympus pen dial

Olympus Pen W shutter speed dial

Set to 1/30 second; the choice is restricted, just 1/8 second to 1/250, plus B (in green). The Olympus Pen series were 'half frame' (18x24mm) cameras, giving 72 frames on a 36-exposure full-frame film. This is a leaf shutter again.

Considerations when choosing a shutter speed

Although the sole purpose of the shutter is to govern the amount of time the film or sensor is exposed, there are two separate considerations when it comes to choosing the best shutter speed for a particular picture. One is exposure determination. In bright light, you need a shorter shutter speed or a smaller lens aperture or both.

 

In poor light, you need a longer shutter speed or a wider lens aperture or both: apertures are covered in more detail in the free Basics modules on lenses and focus and depth of field.

 

Café, Athens

There's not much light, so you need the maximum aperture your lens can manage (here, f/1.4 on Roger's 35mm Summilux, on his Leica M4-P), and a long-ish shutter speed too: here, probably 1/30 or even 1/15 second. There's also the problem that the light is a horrible mercury-vapour green, so a lot of post-production in Adobe Photoshop was needed to get even a tolerable colour balance. Contrast is too high, too. Digital is often much superior in this regard.

 

cafe, rhodes

 

Often, you have a wide choice of shutter speed/aperture combinations, all of which will give the same exposure. It's simple enough: open up one stop (e.g. from f/4 to f/2.8) and you double the amount of light coming through the lens. You therefore have to halve the shutter speed (e.g. from 1/125 to 1/250 second) to get the same exposure. Close down one stop (e.g. from f/5.6 to f/8) and you halve the amount of light coming through the lens. You therefore have to double the shutter speed (e.g. 1/30 to 1/15 second) to get the same exposure. At this point, it is always a trade-off between shutter speed and aperture, and each will have its own imperative.

Camera shake

If you don't hold the camera steady, it can move during the exposure, and the picture will be blurred. The blur may be so bad you can barely see the subject, or so slight that it merely takes the ultimate edge off the lens resolution.

Numerous factors influence camera shake. Are you relaxed and well fed? Or tired and hungry? Have you just been running? How comfortable is the camera to hold? How smooth is the shutter release, and how good are you at squeezing it instead of stabbing it? How big are you going to enlarge the final picture? The bigger the degree of enlargement, after all, the more obvious the shake will be. And what focal length lens are you using? The longer the focal length, the more the shake will be magnified.

 

Ruined spa, Slovakia

One of the prime requirements here was for maximum sharpness from front to back. As the subject is not going anywhere, and there are no people moving in the subject, it makes sense to use a tripod -- which is exactly what Frances did, shooting Ilford HP5 Plus in her Voigtländer Bessa-T with 35/2.5 Color-Skopar lens and a yellow filter from B+W. The print is on Ilford Multigrade Warmtone. The tripod was a Slik Snapman which weighs only 1 kg (2 lb 3 oz) and is more than big enough for a 35mm camera.

An old rule of thumb for 35mm is that you can hold the camera steady at 1/focal length (in mm), so you can hold a 35mm lens at 1/35 (call it 1/30), a 200mm lens at 1/200 (call it 1/250) and so forth. It's better than no rule of thumb at all, but you can afford to be more relaxed with shorter lenses, i.e. you might get away with 1/8 second with a 15mm lens, but even 1/250 may be pushing your luck with a 200mm. Generally, you will see a detectable improvement if you go up another step on the shutter speed dial. Or use a tripod...

Also, the rule of thumb applies only to 35mm. With an 80mm lens on a roll-film camera, you can often get away with 1/30 second, because the image is enlarged that much less -- and in the days of 4x5 inch press cameras, they would often use 1/10, 1/5 or even 1/2 second with a 5 inch (127mm) lens.

Shutter speeds for specific purposes

You may want a very long shutter speed (with the camera on a tripod), for example to capture the streaks of light left by moving traffic or to make a 'cotton candy' waterfall; or you may want a very short shutter speed, to 'freeze' rapid motion; or an in-between shutter speed so that you can hand-hold the camera steady, without any risk of camera shake, at a useful middling aperture, even if the subject is static or slow moving.

 

 

Le Mans 24-hour race

This is perhaps an extreme case of a long shutter speed, as you have to be told what the subject is before you can really see it, but we think it captures quite well the speed of a Le Mans car just after nightfall.

There is both subject movement (the car, obviously) and camera movement (Roger followed the car in the viewfinder, 'panning' with the direction of travel) and the result is definitely impressionistic.

The camera was almost certainly a Nikon F, because that's what we used in those days (1982) but lens and film details are long forgotten.

 

le mans blur

 

Apertures for specific purposes

You may not be too worried about shutter speed, but may want a small aperture for maximum depth of field, or a large aperture so that the subject is in sharp focus and stands out against an out-of-focus background.

 

grass, over-x

 

Frosty grass

The 135/2.8 Tele-Elmarit-M has a close focusing limit of about 1.6 metres, 5 feet, and at full aperture at this distance, as here, depth of field is wafer-thin. Indeed, even at f/4 or f/5.6, the background would probably still be completely out of focus. It needs to be, in order to isolate the subject. Roger actually mounted the lens on the M8 digital camera, where thanks to the 18x27mm sensor, its equivalent focal length is 180mm. Using the lens at full aperture also allowed the use of a very short shutter speed, which is always a good idea when using long lenses hand-held.

Compromise

Because shutter speed and aperture are so intimately related when it comes to exposure -- if you increase one, you have to decrease the other -- it often happens that you have to compromise between the two. Usually, this means that you have to choose between a fast shutter speed for action stopping or avoiding camera shake, and a smaller aperture that would give you more depth of field. So let's look at an actual example.

Let's say that your choice of shutter speed/aperture combinations is as given below. All will result in the same overall exposure, and most auto-exposure cameras would probably set something around the middle exposure, 1/125 at f/8. So why would you choose anything else?

 

Speed/Aperture Combination

Advantages

Disadvantages

 

1/8 second at f/32

Maximum possible depth of field (see the free focus module in Basics), especially important with extreme close-ups. Possibility of interesting blur from subject or camera movement.

Lens stopped down too far for optimum resolution (see focus module), speed too slow to 'freeze' any but the slowest movement, virtual certainty of camera shake unless you use a tripod. Few lenses for 35mm allow f/32.

 

1/15 second at f/22

 

Much as above -- and your only choice for these effects if the lens stops at f/22.

 

Much as above, though you might get away with hand-holding a 15mm at this speed.

 

1/30 second at f/16

 

A good realistic compromise if you want good depth of field without too much loss of resolution, together with a fair chance of holding the camera reasonably steady with standard or wide-angle lenses.

 

Still not much scope for freezing action, and you'll probably get a sharper picture with a tripod.

 

1/60 second at f/11

 

Probably the best compromise for a hand-held shot if you want maximum depth of field, unless camera shake is likely to be a problem.

 

As above

 

1/125 second at f/8

 

A great compromise for street or reportage photography

 

'Middle of the road' combination that doesn't give you interesting blur or selective focus or maximum depth of field.

 

1/250 second at f/5.6

 

As above, except that you have to focus more carefully. Good 'freezing' of most motion.

 

Depth of field may be a bit limited for some subjects

 

1/500 second at f/4

 

Probably the best choice with a long lens (over 4x 'standard' focal length) to avoid camera shake. Excellent 'freezing' of motion.

 

Depth of field is getting quite small; you need to focus carefully.

 

1/1000 second at f/2.8

 

Even better 'freezing' of motion, even less risk of camera shake. Sharply focused subjects will stand out better against an out-of-focus background.

 

Useless if you want much depth of field, except with very distant shots.

 

1/2000 second at f/2

 

As above, only more so. Few long lenses are likely to be as fast as f/2.

 

Depth of field falls to almost nothing, especially with close-up subjects.

 

 

 

'Chinese' nets and little girl

Depth of field is clearly important here, but absolute maximum definition at infinity is not required because haze and a lack of resoluble detail means that we don't really care what is going on in the far distance. Even with the slow film used here (Fuji RF ISO 50) Roger was able to use 1/125 at f/8 or thereabouts with his 35mm f/1.4 Summilux on his Leica M4-P. A shutter speed of 1/125 with a 35mm lens allows as much resolution as you can reasonably expect from a hand-held shot -- all of which helps explain why the 35mm focal length on 35mm is his favourite for general photography. That, and it suits the way he sees the world.

 

chinese nets

 

Film Speeds

There is a whole free module on ISO film speeds, but all you need to know for the moment is that the higher the ISO speed, the less light a film needs to give you an image. The progression is arithmetical, so 100 is half as fast as 200 and 200 is half as fast as 400. We unreservedly recommend ISO 400 films for beginners; others recommend 200, which is usually cheaper, and even 100 is fine, except that when light levels fall, you will need longer shutter speeds or wider apertures or both. Speeds for digital sensors are not fully standardized but are given by analogy with film speeds; we recommend 100 to 400 for use in good light, and faster speeds when you need them. Being able to set sensor speeds on a shot-by-shot basis, if you need to, is one of the great advantages of digital.

Determining Exposure

There are whole paid modules on this (for negatives and slides) but the most important thing to remember is that a meter's recommendations are necessarily based on 'average' subjects with 'average' exposure. For very reflective subjects (snow scenes, a white cat on a white sofa) the meter will recommend under-exposure, i.e. you need to give a stop or two extra. For very dark subjects (e.g. a black cat in a coal cellar), the meter will recommend over-exposure, i.e. you need to give a stop or two less exposure.

 

milk boiler

 

 

A lot will depend, too, on where you point your meter -- hence the advice often given to 'favour' the shadows (point the meter more towards the darker areas) when metering for negative film.

But for negative film, which is the only sensible choice for the beginner who chooses film, the best advice is always to err on the side of over-exposure. You can also bracket your exposures (free module).

 

Hot-milk-wallah, Agra

 

Where you point your meter can make an enormous difference. Here, the large dark area would induce the average meter to recommend too much exposure, resulting in the milk-wallah himself being far too light. This can be recovered at the printing stage: if you can see clear detail in the negative, it is entirely reasonable to demand a reprint.

This is of course one strong argument for processing and printing your pictures yourself, whether you start out with a digital image or (as here) scanned film: Roger shot this with his Leica M4-P and 35/1.4 Summilux on Kodachrome, though colour negative (print) film offers much more latitude (see below) and is for the beginner a much better bet.

Latitude

 

This is the ability of a film (or digital sensor) to tolerate under- and over-exposure, and still give an acceptable image. Negative films can't tolerate much under-exposure -- half a stop, maybe a stop (half the optimum exposure) if you're lucky -- but they can tolerate very considerable over-exposure: a couple of stops (4x the optimum exposure) will reduce sharpness somewhat, but the quality loss will still be less than at 1 stop under, and it is entirely possible that three or possibly four stops (8x and 16x) will give acceptable exposures for many purposes. Single-use cameras rely on this latitude.

Digital sensors have much less latitude, but you can always check and re-shoot. Slide (transparency, reversal) films probably have more latitude than most digital sensors, and you can always bracket, but they are not recommended for beginners.

 

Palm trees, India

The central exposure is pretty much spot on; the other two are one stop over (the lighter one) and one stop under, respectively. These frames are on Fuji Astia slide film, which has very little latitude, but the +1 frame is usable as it stands and could be improved in Adobe Photoshop; the -1 frame would definitely require manipulation in Photoshop, but could be made usable. If they had been shot on negative film (colour or black and white), the loss of quality in the +1 exposure would have been negligible for most purposes. These pictures are from the free module on bracketing.

palm, bracket

The bottom line

Exposure is nothing like as hard to master as some people would like you to believe, and a wide range of exposures is likely to be acceptable, especially to the beginner. Yes, it is worth learning how to give the best possible exposure, first time without experiment or bracketing, but it's not necessarily urgent for the beginner. When you are ready to learn more, there is plenty of information here on the site, including the way that exposure determination should be approached differently for negatives and slides (paid modules).

 

beach, goa

 

Beach, Goa

In hard, contrasty light like this, exposure is more difficult than in soft, overcast light: you can see that Roger 'lost' the face of the man on the centre left. Under such lighting, avoid contrasty, high-saturation films (often marketed as 'extra color' or 'super saturated') or, with digital cameras, reduce the contrast setting on the camera. It's a good idea to bracket, too. The big area of light sand will encourage under-exposure, so give one exposure at the meter's recommendation and another at one or even two stops more. With negative film, this should work fine. Unfortunately Roger's Leica (with 35/1.4 Summilux) was loaded with slide film...

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© 2007 Roger W. Hicks