EOS R7 Sensor read out speed versus shutter speed when using electronic shutter

[swetzel9]

I think I have a fairly good understanding of electronic, mechanical, and electronic first curtain shutter functionality. But there’s one bit I’m puzzled on.  Can someone help me understand how the shutter speed of an image can be fast faster than the image read out time when using electronic shutter?

I have an R7 and the shutter readout speed is approximately 29 ms or about 1/33rd of a second according to what I can find on the web. But I can obviously set the shutter speed to be much higher than that. How exactly does that work if the sensor read out time takes 1/33 and my shutter speed is set to 1/1000

is the exposure time of each individual pixel or chunk of the sensor getting read out 1/1000? But the overall image will always take 1/33 of a second to be captured?

Thanks

[Waddizzle]

Maybe an explanation “rolling shutter” is a good start.  Keep in mind that the entire sensor isn’t read at once.

https://en.m.wikipedia.org/wiki/Rolling_shutter 

What is the maximum frame rate of the camera?  With a 27ms readout speed, that’s going to be the limiting factor in maximum frame rate.  I would guess the max fps is around 30 fps.  

Here’s an analogy that might help.  In this analogy I will use water, instead of light.

Imagine you have a faucet with a very fast gate valve, which basically means a barrier that lifts up to release water and lowers down to stop water flow.  This is the equivalent of a mechanical shutter.  It’s holding back high pressure water.

There’s a bucket (or sink) under the faucet that can catch the water coming out the faucet.  Now imagine the bucket has several rows of cups that hold water.  Each cup has a hole in the bottom to drain the bucket.  But, only one drain hole can be opened at a time.  

To drain the bucket, you must open the hole in each row one by one.  Each hole only drains its water cup.  This process takes time. 

Let’s slow your numbers down by a factor of 100.  Lets open the valve for 1/100 of second and close it.  Now it’s going to take 1/3 of a second to drain the bucket.  That’s how a mechanical shutter system works.

An electronic shutter system moves the valve.  Each water cup now has its own valve. Each will open for the same 1/100 of a second.  

Here’s the key difference. The.  The mini-valve for each water cup doesn’t open at the same time.  The valves don’t open at the same time.  They don’t open until they are being read! 

Because the cups capture light at different times, this is what causes rolling shutter. It still takes 1/3 of a second to drain the whole bucket.  And, each cup is filled for only 1/100 of a second, just not at the same time!