Mechanical shutter

This article is a continuation of a series of articles on issues raised earlier in the articles'Shutter noise'and'Disadvantages of modern DSLR cameras'.

Mechanical shutter

Mechanical shutter

Modern digital cameras use focal shutters of a curtain-slot type with a vertical stroke of the blinds. This means that such a shutter is located immediately in front of the camera’s matrix, consists of shutters that move vertically (usually from top to bottom and back).

The following illustrates how the shutter is released:

1 video.

Pay attention to how much shakes the mirror after lifting and returning, as well as how shutter curtains tremble monstrously... The video shows that the shutter curtains consist of several parts (the so-called slats or 'louvers').

2 video.

In this video, you can notice the gap that forms during the movement of the shutter curtains.

3 Videos.

Full-format camera and cropped camera.

4 video.

Shakes not only the mirror and shutter shutters, but also the aperture blades.

And a little discussion about the shutter, using the camera as an example Nikon D80.

Exposure The synchronization of this camera is 1/200 second. This means that it is precisely this period of time that the shutter curtains need to travel a distance equal to the height of the matrix.

If you need to shoot at shutter speeds slower or equal shutter speed synchronization, then the shutter will work as follows:

  1. The first curtain opens, it takes 1/200 second.
  2. Held Exposition, at this time, the matrix remains fully open. Take the shutter speed 1/60 second as an example. The second curtain starts its movement 1/60 second after the start of the movement of the first curtain.
  3. The second curtain closes, it takes 1/200 second.
  4. The curtains rise together to their initial position.

At such shutter speeds, it is easy to synchronize the flash and shutter. Usually, the flash fires after the first curtain (as soon as the shutter fully opens the matrix), or before the second curtain begins to move (before the shutter closes). For example, the impulse of my Nikon flash SB-910 has a duration from 1 \ 800 s to 1 \ 40.000 s depending on the power. When the flash fires, the camera’s sensor is fully open and there is no synchronization problem.

If you need to shoot faster excerpts synchronization, then the shutter will work as follows:

  1. The first curtain opens.
  2. The second curtain does not expect a full opening of the matrix and begins its movement after the first. The delay of the second curtain determines the time exposure. Take, for example, the shortest shutter speed allowed for Nikon D80 - 1/4000 p. In this case, the second curtain begins its movement in 1/4000 s after the start of the first curtain movement, and thus the two curtains move together, forming a moving slit, which produces the exposure.
  3. The curtains rise together to their starting position.

It is difficult to synchronize the flash with the shutter at such speeds. If the flash fires only at a certain moment, then in the picture we will get a strip, which is formed by the shutter slit. To get around this limitation, high-speed sync flash units are used that “light” the entire time both shutters move to avoid streaking.

Interestingly, if we shoot for 1/60 of a second, then the shutter actually needs much more time for its work. So, it takes 1/60 s to lower the first curtain and wait for the second, 1/200 s to move the second curtain and at least another 1/200 s to lift both curtains to their original position (perfect case, in reality, you need more time). Total 1/60 + 1/200 + 1/200 = 2/75 s. If you remove the restrictions on the operation of the mirror, aperture and processor of the camera, then in one second under ideal conditions it will be possible to take no more than 38 frames, and this is mechanical restriction of burst shooting.

At the same time, cameras that use the electronic shutter, which does not need to spend time on the movement of the curtains, can now easily shoot at 60 frames per second in photo mode (as an example, look at Nikon 1 J1). Just imagine how useful it would be for photojournalists and sports photographers to photograph certain events at such tremendous speed. For example, the fastest DSLR for 2014, the Canon 1DX, shoots at a maximum of 14 frames per second, which is 4 times lower than the 60 fps of some electronic shutter mirrorless cameras. The only problem is that modern cameras with an electronic shutter have their drawbacks, for example, they suffer from 'rolling shutter', etc. and for now, one can only dream of an electronic shutter that has the positive qualities of a mechanical shutter and a huge shooting speed.

By the way, the “real” speed of the shutter curtains is easy to calculate. Matrix height Nikon D80 is 15,8 mm, the shutter passes this distance in 1/200 second, and its speed is 3,16 m / s or 11,38 km / h, which is quite a bit :)

Thank you for attention. Arkady Shapoval.

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Comments: 70, on the topic: Mechanical shutter

  • Vladimir

    Tell me, why do modern cameras (like the latest Sony) still use a mechanical shutter? What is the sacred meaning if electric shutters already exist and work? I know that this is somehow related to the effect of the Rolling Shutter, but I don’t understand how.

    • Arkady Shapoval

      Because there is still no cheap global electronic shutter on modern cameras. And in ordinary Rolling Shutter is still very strong.

      • Vladimir

        Why does everyone talk about the problem of creating a cheap global shutter, if for about 10 years progressive-scan matrices have been implemented in video cameras? Of course, there is less matrix resolution, but still 2 megapixels in professional cameras for a long time, and today they grow like mushrooms of a 4K camera, i.e. 8 megapixels and all with progressive scan (at 25, 50 fps).

        • BB

          50 fps is roughly 1/50 of a second, which is too slow for a photo. But the trick is that the 'rolling shutter' effect is less noticeable in the video, especially if an object is moving in the frame, and the camera is stationary. As well as less noticeable blur from movement: for example, a video of 25 fps and a shutter speed of about 1/25 looks quite normal even with fast movement (as an example, dancing or figure skating) in the frame. Only stationary objects can be photographed at 1/25 without blur

  • Eugene

    Tell me how the Nikon 750 curtains work while shooting a video, the principle of operation. I can not understand. Video resolutions are understandable. The frame rate is the refresh rate of the matrix.
    from 24 to 60. But the shutter speed is 1/30, 1/60, 1,125. Is this the work of the lamellas on the matrix? It turns out that the lamellas are triggered with a frequency of, for example, 1/60 during the entire video filming?

    • Victor

      Comrade, you are exactly one month late :-D

    • Novel

      The shutter does not work in any way while shooting a video. The frame is exposed for a certain time, then read into the buffer. Then there is a pause when the image just goes to the screen, then again.

      I'm more interested in the question of how exposure works on ultra-high-speed cameras. But too lazy to dig.

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