Does the Sony A77 use a mechanical shutter with its translucent mirror design?

Asked 2/10/2012

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I’m trying to understand how the Sony A77’s translucent mirror system works. Does the camera still have a shutter, and if so is it a mechanical shutter that’s physically operating during 12 fps continuous shooting?

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

14y ago

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Yes, the A77 has a mechanical shutter and it does move at 12 FPS per second. There are a number of cameras with similar shutter-speeds including some ultra-zooms but indeed this is very fast.

What it does not have is a motor to move the mirror. This is more problematic for speed then the shutter itself since a mirror is heavy and has to move out of the way completely and back that fast.

Instead it has semi-transparent mirror (transluscent is not the right word technically). The mirror is made of flexible material that reflects about 30% of the light and lets the rest straight through. This makes the imaging sensor have to work a little harder but the autofocus sensor more so.

Originally by user1620. Source · Licensed CC BY-SA 4.0

user1620

14y ago

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Yes. The Sony A77 still uses a mechanical shutter, and during 12 fps burst shooting it is physically cycling for each frame. What the SLT/translucent mirror design changes is the mirror mechanism, not the shutter itself.

Instead of a traditional DSLR mirror that flips up and down for every shot, the A77 uses a fixed semi-transparent mirror. Part of the light is reflected to the autofocus system and the rest passes through to the imaging sensor. Because the mirror does not have to move, the camera can shoot faster and maintain autofocus more easily during bursts.

The A77 can also use an electronic first-curtain shutter setting, which pre-opens the mechanical shutter and starts the exposure electronically. This helps reduce shutter lag and noise. But the camera still relies on a mechanical shutter overall for normal still capture.

So the short answer is: fixed mirror, yes; moving mirror, no; mechanical shutter, yes.

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14y ago

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