# How does the mechanical shutter work in a mirrorless camera (e.g. EOS R5)



## mrfig (Jul 28, 2020)

Sorry for the ignorance, but the thought just occurred to me and I would like to understand how it works. The image that is seen in the viewfinder is coming from the image sensor, so the mechanical shutter would need to be open most of the time, would it not? So what happens when a single photo is taken? When the shutter button is depressed for a single photo, does the shutter close, open (this is where the image is captured - I'm guessing that this image is also transferred to the viewfinder to minimize viewfinder blackout? ), close and then open (so the image is restored in the viewfinder) again for a single photo? What is going on when you take a burst of photos (12 fps in the case of the R5)? I'm guessing that when the shutter button is depressed, the shutter closes to begin the burst and then works like a normal camera during the burst - transmitting each image taken to the viewfinder - until the shutter button is released at which time the shutter returns to full open?

This is what seems would be happening, but I just wanted to make sure that I understand what is happening. It seems like for single images the camera goes through two full shutter actuations?


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## gruhl28 (Jul 28, 2020)

For a camera that doesn't use electronic first curtain, I believe your description is correct. I believe some cameras with electronic first curtain are able to skip the initial closure of the shutter. And for electronic first and second curtain the shutter never closes. I'm not 100% certain of my understanding, but I think this is correct.


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## Kit Lens Jockey (Jul 28, 2020)

gruhl28 said:


> For a camera that doesn't use electronic first curtain, I believe your description is correct. I believe some cameras with electronic first curtain are able to skip the initial closure of the shutter. And for electronic first and second curtain the shutter never closes. I'm not 100% certain of my understanding, but I think this is correct.


This is pretty much correct. Most modern mirrorless cameras, including Canons, let you choose how you want the shutter to operate.

Using a full mechanical shutter means that the shutter is open when you're looking through the viewfinder, then when you press the shutter button, the shutter immediately closes, and then to take the photo it opens and closes again, just like it would on a DSLR (then it opens once again to keep the video feed going to the EVF or the rear screen.) As far as what shows up in the EVF, it may freeze up or black out briefly during this.

Using electronic first curtain, the shutter is open when you're looking through the viewfinder, then when you press the shutter button, the shutter remains open, the camera electronically begins recording the exposure, and then the shutter closes, ending the exposure (then it opens once again to keep the video feed going to the EVF or the rear screen.) Again, the EVF might black out or freeze up during this.

Using the full electronic shutter, the shutter doesn't move at all. It's open the whole time. The camera just electronically starts and stops recording the light hitting the sensor to make your exposure. Some of the best cameras can keep a smooth video feed going to the EVF even during shooting when using the full electronic shutter.

Because most current sensors don't electronically read out all at once, you can get some weird artifacts or distortions when using the full electronic shutter. They can also cause problems with using flashes. That's why we still have mechanical shutters on mirrorless cameras.

Theoretically, somebody correct me if I'm wrong, but once camera makers develop and implement sensors that read out all at once instead of line by line (called a "global" shutter), there would be no more need for a mechanical shutter at all.


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## john1970 (Jul 28, 2020)

I believe that is correct that once an electronic global shutter becomes available mechanical shutters should no longer be needed. A global FF sensor with dual gain output would be an amazing advancement.


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## mrfig (Jul 29, 2020)

Thank you for all your feedback! Very helpful!!


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## Proscribo (Jul 29, 2020)

Kit Lens Jockey said:


> Theoretically, somebody correct me if I'm wrong, but once camera makers develop and implement sensors that read out all at once instead of line by line (called a "global" shutter), there would be no more need for a mechanical shutter at all.


Line by line is enough if it is faster than the mechanical shutter (those are around 1/200-1/300s), if it is easier than implementing a global shutter.
Tho you'd want one mechanical curtain to be left in there for dark frames.


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## SteveC (Jul 29, 2020)

Kit Lens Jockey said:


> Theoretically, somebody correct me if I'm wrong, but once camera makers develop and implement sensors that read out all at once instead of line by line (called a "global" shutter), there would be no more need for a mechanical shutter at all.



The fundamental problem is being able to read all that data simultaneously then push it out simultaneously, and that would involve millions of wires instead of a couple of dozen.

I could imagine a sensor chip with a buffer behind the pixels, when the "shutter closes" every sensor pixel is instantly copied to the buffer pixel, then it's read out of the buffer line by line. That would still involve millions of wires (pixels to buffer) but those would be in the chip, which is doable.

But such would require two layers of fabrication with the silicon (?) wafer, and I don't know if they can do that yet.


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