Curtain shutter. Shutter of the camera. How to live with it now
Camera shutter is an invisible, but especially important element of the photographic system. The camera shutter is not visible to the photographer, but is always audible.
What is the shutter of the camera? Why do we need a camera shutter?
The shutter of the camera plays one of the most important roles in capturing an image onto a film or digital matrix. The main task of the shutter is to regulate the duration of the passage of light through the camera's optical system to the photosensitive element of the camera.
Focal slide horizontal travel
The flash can be started at the moment when both curtains were fully open. This fully open time with zero time makes the exposure time the passage time when opening the curtain. This also makes one curtain time equal to the maximum synchronization speed by definition. Thus, the faster moving shutter mechanisms are what also creates a faster maximum synchronization, which is the maximum speed that the shutter bolt can fully open for a flash.
If you know the word (time of capturing the image by the camera), then the camera shutter is the main device that allows you to control this time.
What happens when you take a shutter?
The shutter of the camera is a mechanical device. The shutter is in most cases a curtain (vertical or horizontal). It should be understood that there is a minimum time for which these curtains will have time to open and close, allowing the light to pass to the film or exposing the frame.
Maximum synchronization speed of the focal shutter
Modern blinds move the short dimension vertically down the frame to be faster than moving over the longer frame size. For those who are interested in the numbers of the maximum speed of synchronization of the shutter with the focal plane. Two shutters of the shutter of the focal plane are installed in front of the camera sensor. The first curtain is usually closed, and the second curtain is usually open, and this amount is not illuminated at all. Nikon calls them the front and back curtain. The canon calls them the First and Second Curtain.
This is how the camera's shutter looks:
This is how the shutter on the film chamber looks when the back cover is opened:
So how does the camera shutter work? in the event that the exposures become super-short (1/5000 or 1/7000). In this case, digital cameras have a digital shutter, electronically controlled and. The physical shutter of the camera with ultra-short exposures can open and close at its maximum speed, at the time of which, a digital signal is received to begin capturing the image and after a moment the signal to stop responding to the light flux.
These are rotatable curtains, similar to the old shades of the window. Early cameras used fabric curtains, today a thin curtain of titanium foil is used for durability. On the shutter release button, the first curtain opens, retracting to move around the frame. At the first moment this provides only the leading edge of the frame, and the rest of the frame is dark, but it glows after the shutter moves to open more. The parts of the frame still receive light until the closing bolt passes them.
But the fully open position should wait a little longer for 0 to skip the maximum expected flash duration. But to a large extent, the maximum synchronization speed is also the time for the movement of one curtain. A faster shutter speed can not include a fully open moment for flash transmission. Faster shutter curtains provide faster synchronization.
You ask: why do we need curtains in the camera (the shutter of the camera). So in modern digital cameras, in most cases, the shutter plays the role of protection against getting dust and dirt on it, which can permanently disable it. A camera is the most expensive element of a digital camera.
This is how the matrix of the digital camera looks when the mirror is lifted and the shutter curtain is open:
Curtain-slotted focal jaws
The maximum sync speed is the exposure time necessary for the first curtain to fully open, since any less impact means that the second curtain has already started to close. For faster shutter speed, the second curtain begins to close before the first curtain fully opens.
The principle of the curtain shutter
For longer exposures, say, one second of exposure, the second curtain simply waits one second before closing. The shutter is fully open all this time. Distortion of objects: But the leading edge is exposed ahead of time than the trailing edge, at which fast shutter speeds can distort the movement captured during this time. The front and back edges are subjected to the same duration, but at slightly different times.
The matrix or film is not visible, because it is completely covered by a mirror, which allows you to see in the viewfinder an accurate picture from the lens.
The camera shutter serves to dose light onto the photographic material. The speed of the shutter is set such an option as. The gates have different variations of performance and types, but we will consider curtain-slotted focal gates.
Behind the curtain of the back curtain follows the front curtain. The frame never opens completely. This provides only a narrow width of the open slot. The flash can not work because the frame never opens completely to transmit it. The total movement of the curtain takes longer than exposure from a narrow slit, but the actual exposure time is the time of an open slot above any area.
The advantage of the focal plane shutters: the same remarkable accuracy mechanism moves like curtains, creating and moving a virtual narrow opening slot on the frame at a fixed speed to provide an accurate fast exposure under this slit. There are really good reasons why the best cameras provide a shutter to the focal plane.
Curtain-slotted focal jaws
The focal shutter is very close to the surface of the film (focal plane), from that and the name. It is curtain-slotted because usually the shutter consists of two curtains, which create a gap between them during the motion, through which the frame shines. There are two common types of focal shutters small format photographic equipment:
Different transmission variables and springs for selecting the shutter speed are no longer needed or used. Regardless of the shutter speed, the speed of the two-curtain gear motor is always at the same fixed speed from one engine, which can be made very accurate and constant. The value of the shutter speed is just the time between the start of the two curtains, which in modern cameras with processors is performed using a timer with a crystal clock mechanism, very accurate. But this engine speed does not actually control the exposure time. . Disadvantages of the shutters of the focal plane.
Focal slide horizontal travel
"Horizontal travel" means that the shutter operates on the long side (the shutters walk along) the frame. The most common "curtain" focal flaps of the horizontal stroke were used in small format cameras almost everywhere, and before the beginning of the 2000th (the longest used in).
How fast is the maximum flash sync speed?
However, the two curtains have a higher shutter speed, so that exposures of different parts of the frame under this movable slot occur at several different times. The disadvantage of the flash is that at these higher shutter speeds, the opening of the shutter occurs only under this narrow slit. Instant flash then illuminates what is under this narrow slit at that moment, and the rest of the frame is not affected by the flash. Therefore, we can only use a flash with a shutter speed slow enough so that the entire frame is open at the same time to allow a quick flash to expose the entire area of the frame. This is a very small problem in the room where we use the flash, because the environment fades and does not cause any blurring. This may be a problem for the flash in a bright environment, such as sunlight, since a camera with a shutter of the focal plane using a flash usually does not allow you to set the shutter speed faster than the maximum sync speed. The flash is relatively instant, but it needs to be synchronized when it fires when the shutter is fully open.
The main disadvantage of a shutter with a horizontal stroke in its high-speed synchronization for shooting with an electronic flash, for which the limit is often 1/60 - 1/90 second, and also the impossibility of stable operation at high speeds (from 1/1000 sec.).
I think that's why most of the curtains, which were equipped with Soviet SLR cameras, did not have a speed higher than 1/500 sec.
How to live with it now
For shutters in the focal plane, the maximum shutter speed at which the full frame is fully open at any time is called the maximum synchronization rate. Flash synchronization is not possible if the shutter speed of the focal plane is above this limit.
Some cameras use leaf blinds in each lens or electronic shutters in some camera sensor chips, and they can synchronize faster than the shutters of the focal plane. The maximum synchronization speed for the shutter of the focal plane is related to how quickly the curtain can move across the frame to the "Fully Open" position.
Blind shutter of Zenit-ET camera
To use the electronic flash, the shutter is set to the so-called "sync speed" (on the shutter speed dial, the shutter speed is denoted as X, or can have a synchronization rate add-on, for example X / 60), which provides the minimum exposure delay, flash to light the frame just at the moment when the shutter is fully open.
The maximum synchronization rate is usually not a speed problem, since the flash works faster, so the maximum synchronization speed is excellent. Slowdown is a bright daylight environment, unable to use a faster shutter speed. Even in the camera's manual mode, the camera will not allow you to select these fast shutter speeds if it knows that a flash is present. Of course, there is no reason for this, except to show the problem here.
Historically in the distant past, the only way to get around this synchronization problem with a faster shutter is to use a special flash that burns longer and remains fully lit for longer, since the total time of the shutter movement is more like a continuous light for the duration of the shutter.
In any other scenario, there will be an uneven light of the frame.
Focal flap vertical stroke
In the focal gate of the vertical stroke, the shutters walk along the short side (across) of the frame. These closures are more complicated in design, but their performance characteristics are more stable, including at high speeds. Modern shutters in digital SLR cameras are lamellar, vertical, electronically controlled.
The outbreaks took several milliseconds to fully ignite and become bright, so they had to be launched before the shutter, and the shutter had to wait until they were bright. Incandescent lamps also had guide numbers on the package. Limiting the shutter speed for maximum synchronization speed does not really matter much for a flash in the room. The flash is very fast, so when the illumination is reduced, the shutter speed is slower, the flash is faster. The dim exterior is too dim to blur the movement observed by the slow shutter, and in the room we can open the diaphragm as widely as we would like without worrying about overexertion of the environment.
Moreover, the speed of activation and the initial impulse determines the electric motor, and the shutter speed is already controlled by the electromagnets. Hence the increased power consumption of the system at long exposures.
Lamellar shutter Canon 40D, the motor of the shutter, mirrors.
But this maximum synchronization speed becomes a much more serious problem when using fill in the bright sun. The frequency of light is very fast in dim light, without the environment to blur anything, but the bright sun is continuous, not fast.
Desirable thinking, but our dream is that if we could increase the shutter speed, we could open the aperture, reduced depth of field or equivalent exposure for daylight, which allows the normal flash mode to operate at a lower power level, without affecting either impact. Or, a faster shutter speed can help the flash to "overcome" the sun, reducing the sun, without affecting the flash - if we could, but we can not. We are against the maximum wall of the sync shutter speed.
To synchronize the flash at high speeds, a so-called preflash or stroboscopic flash is used. It generates several pulses in one pass of the shutter curtains, thereby solving the synchronization problem. Usually, even the most inexpensive modern electronic flashes support these modes.
Material of manufacture and reliability
Curtains
The material of manufacturing curtains in the overwhelming majority was a rubberized fabric. Despite its simplicity and cheapness, curtain fabric closures have very unpleasant features:
But they have the same effect on both the flash and the sun, so they do not change the balance between the flash output and the sun. A flash in the bright sun is a special case. The speed of flash synchronization is just a problem in the bright sun. It does not matter in the light of the world, where we need a flash. Today the situation is better than ever before.
One way to bypass sunlight is to underexpose sunlight for a couple of stops, so the flash can stop the movement without clouding it again. The flash becomes the primary light instead of filling. Sports action like this, it still emphasizes the subject. The LED is faster than the shutter, and reducing the exposure of the sun leads to less blurring of the action. And the speed of light is a way of shooting high speed.
- Burn in the sun
If you forget to close the lens of the camera with a lid, then the lens will act like a magnifying lens, and in the end, the properties of the rubber change to such an extent that it crumbles, "burns out."
- Elements of the curtain are subject to abrasion
Often there are cameras of one or another manufacturer, the cloth shutter rods in which are simply torn due to wear and tear.
Several factors of confusion that do not change the basics. It is also easy to use this function as an inexpensive electronic shutter instead of a more expensive mechanical shutter. But the time when it is on, can be synchronized and used as a shutter. However, without a protective coating that also covers the chip, this additional accumulation of light can cause a flash called flowering. The fast electronic shutter speed provides an image, but the flash is caused by the longer duration of the slow mechanical shutter, while the chip is not closed, but not protected from the sun. The best shutter of the focal plane is considered a very big plus for several reasons, however the fastest synchronization speed with the flash is not one of its functions. However, with these electronic shutters, if you can break the connection to deceive the camera so that it does not recognize the flash, then camera flashing will not limit the shutter speed at all.
- Elements of the curtain are detached from the tensioners
Over time, the adhesive component of the adhesive base becomes unusable, and dries up. The curtains are peeled off at the base of the tensioners.
- Springs tensioners are out of order
Inside the tensioners there are steel springs, which lose their properties with time. The problem is eliminated by twisting the adjusting screws and not as scary as those listed above.
On the printout, the listed faults can be displayed as underexposure of one of the areas of the frame, uneven exposure throughout the frame (curtains are braked), the image of the frame is fixed with jerks. Seeing such prints, it is worth paying attention to the state of the shutter.
Despite the fact that curtain valves have dangerous illnesses, they are very maintainable, and in order to make repairs in "field" conditions, it is enough to have direct hands and appropriate literature. The maximum lifespan of the curtain shutter is approximately 5,000 operations.
Slatted shutters
The curtains of such closures consist of several metal slats. And, as a material for slats can be used not only steel, but also stainless steel, carbon fiber. The lamellae of digital SLR cameras are electronically controlled using an electric motor and electromagnets.
Electromagnets are responsible for the shutter speed, keeping the shutters open until they receive a pulse from the control chip to open. In practice, it all takes, of course, a split second.
Lamella shutter Canon EOS Kiss
The lamellae were widely used in Japanese cameras, where they were used in the early 1960s. Lamel bolts are safer than curtains, do not burn out in the sun
However, the maintainability of such closures is much less than that of curtains - if the replacement of the lamellae, in principle, still on the hands of the user, then its adjustment is possible only within the walls of the service center (in general, not a cheap pleasure, even if someone takes up this job). Therefore, the lamellar gates change entirely.
Of the faults of the sluice gates, one can find the following:
- Blinding of blinds
- Blindness of blinds
- Breakage in the winding of an electromagnet
- Dropping of buster sleeves from the seats
These malfunctions can mainly occur in shutters with large runs, and also to some extent on fresh chambers during the "run-in" period. Running the shutter goes through about the first thousand trips, after which the shutter can even go on its service life. In the green table, the shutter resource of some Canon cameras is indicated:
Maximum lifetime of the shutter varies. The manufacturer, however, depending on the model of the camera, sets limits from 50,000 operations on junior camera models and up to 500,000 on professional cameras. Often found so that the camera has time to become obsolete, and find a fourth or fifth owner, and the resource of the shutter is not exhausted.
How the Shutter Works
The principle of the curtain shutter
In the illustrations below you can see the principle of the focal shutter with the horizontal stroke of the cloth shutters.
The basic design consists of two opaque curtains, which are installed on the tensioner rollers. Typically, the curtains are arranged so that by default they block the access of light to the photographic material.
When we cock the shutter, the film frame moves simultaneously, and the shutter curtains from its usual places.
By pressing the shutter button, the first curtain is released to start the stroke. On the way of movement, the first curtain passes through the frame of the photographic material, dosing the light.
When the first curtain finishes, the shutter is completely open for a while. 
At the end of the exposure time, the second curtain will block the arrival of light and the exposure will end. 
When the shutter is cocked for the next frame, everything repeats again.
If the shutter operates with a minimum shutter speed, the exposure of the photographic material occurs through the gap between the shutters that catch each other. 
Slatted shutter
The work of the focal flapper of the vertical stroke is clearly seen from this video:
Shutter lag
Or the shutter lag. This is the name of the delay before the shutter releases. The lag can be referred to as a specific delay after pressing the shutter button, and the waiting time until the next shutter release during high-speed shooting.
In general, the problem of delay after pressing the shutter button is inherent in younger / ancient models of digital SLR cameras, as well as various soap dishes and camera phones. The delay effect is due to the slow processing speed of the processor of the device, or the speed of response of the mechanisms in general (for example, autofocus).
Examples
Film speed is limited by the speed of film rewinding, and the lag of the shutter can be called the waiting time before the film reaches the end of the next frame during continuous shooting. The table shows the interval between the operations in continuous shooting of some Canon cameras (green column):
The shutter lag in the older models of the CPC may appear during the buffer overflow of the camera with raw data, then the shutter lag time rests against the recording speed on the card. The buffer fills up quickly, and because of the slow recording speed on the card, the next shutter lag can reach 10-15 seconds.
How to live with it now
The main task of the shutter is to work in with. In this pair, the shutter is responsible for which the light is dosed onto the matrix, or the film of the camera. From all the above written it can be understood that the lamellar focal closures of modern digital SLR cameras have tremendous reliability, but are less repairable, compared to their older brothers, curtains.
By the way, beside curtains in addition to cheapness and maintainability, there was another advantage - they produced less noise and vibrations during photography. And this advantage over time came to naught.
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