How fast is the a7RII silent shutter?

Started Aug 10, 2015 | Discussions
JimKasson
JimKasson Forum Pro • Posts: 29,577
How fast is the a7RII silent shutter?
37

The Sony alpha 7 Mark II (aka a7RII) has a silent shutter mode. When running silent, the mechanical shutter is on vacation, lying back and catching Z’s while the sensor does all the work. The mechanical shutter is a rabbit, completing an exposure in 1/250 second (for shutter speeds faster than that, a slit moves across the sensor, but it takes the slit a little under those 4 milliseconds to make its journey. The fully electronic shutter is a tortoise, taking longer to do its job.

How much longer? I thought I’d find out.

I set up an analog oscilloscope with an input from a function generator. If you’re going to try this at home, don’t try it with a digital scope; it won’t work. I set the time base to 1 msec/division, and the amplitude of the generator to just over the maximum excursion for the scope’s vertical sensitivity. I mounted a 100mm f/2 Zeiss Makro-Planar on the a7RII with a Kipon adapter. I put the RRS plate on the camera and clipped it into a Arca Swiss C1 head on a Gitzo tripod. I set the camera for electronic first curtain shutter, with silent shutter off. I set the camera to manual exposure, and the shutter speed to 1/500 second – that’s two msec. I stopped down a bit and cranked up the ISO to 1600 to get a good exposure.

I took a picture:

Consider the bright part of the trace. If you do that, you can see that it’s about two divisions wide. One division is 1 msec, and we set the shutter to 2 msec, and twice one is two. Isn’t it nice how that worked out? Now notice that the bright part of the image is not vertically oriented, as it would be if every part of the image was exposed in the same 1/500 second. It’s diagonal. Since scope traces from left to right, the fact that the top of the diagonal is left of the bottom means that the shutter exposed the top of the image before it exposed the bottom. Since the image is upside down on the sensor, that means that the a7RII’s mechanical shutter must move from the bottom of the camera to the top.

We can also look at the picture and tell how long the shutter took to go from the bottom of the camera to the top. If we run a line parallel to the diagonal and extend it to the top and bottom of the image like so:

We can see that it takes the shutter a little over three divisions to go from the bottom of the camera to the top. That's 3 plus msec, and the synch speed is 1/250 second, or 4 msec. Looks like the Sony engineers put a little wiggle room in there.

Now, let's change the time base to 10 milliseconds per division (10 msec/div), and take another picture:

Makes the mechanical shutter look pretty fast, doesn't it? Leaving the time base and the exposure time the same, what happens when we turn on the silent shutter?

A lot slower. How fast is it? Let's put in our construction line:

About 8 divisions, or 80 msec. The silent shutter takes 1/12 of a second to complete its travel across the sensor. That's a lot slower than the a7S's 1/30 second. Photographers will have to be careful where and when they use this new feature.

Questions and comments are welcome.

Jim

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JimKasson
OP JimKasson Forum Pro • Posts: 29,577
Inertia in EFCS
5

In the EFCS picture beiow, note that the lines are slightly curved, indicating that the trailing curtain increases its speed as it moves across the image plane, and the electronic leading curtain performs an approximation of that behavior, even though its inertia is presumably zero.

Darn clever, those Sony engineers.

Oh, and the patterns in the light area? My guess is that that's temporal and spatial aliasing with the triangle wave from the function generator. Ain't science fun?

Jim

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JimKasson
OP JimKasson Forum Pro • Posts: 29,577
Faster in APS-C mode!
4

1/20 second.

http://blog.kasson.com/?p=11273

Jim

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Neil189
Neil189 Regular Member • Posts: 269
Re: Faster in APS-C mode!
7

I think I could learn Chinese before I could comprehend what you just described. I hope I don't have to learn what you just said to understand photography and become a decent photographer. I'm doomed.

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JimKasson
OP JimKasson Forum Pro • Posts: 29,577
Re: Faster in APS-C mode!
5

Neil189 wrote:

I think I could learn Chinese before I could comprehend what you just described. I hope I don't have to learn what you just said to understand photography and become a decent photographer. I'm doomed.

Don't worry about all the oscilloscope photographs, unless you don't believe me. Here's the bottom line:

a7RII focal plane shutter travel time:

1/300 second in mechanical shutter mode or electronic first curtain shutter mode.

1/12 second in silent shutter mode.

1/20 second in silent shutter mode when the image size is set to APS-C.

Faster is better, unless you like odd-looking images.

A few examples of focal plane shutter distortion:

https://www.google.com/search?q=focal+plane+shutter+distortion&tbm=isch&tbo=u&source=univ&sa=X&ved=0CDgQsARqFQoTCIzf0trUn8cCFYgcPgodprIEfw&biw=1366&bih=864

Jim

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moffatross
moffatross Senior Member • Posts: 1,128
Re: Faster in APS-C mode!

JimKasson wrote:

1/20 second.

I'm surprised, much as when I first read about the limitations for flash sync'ing using EFCS. My intuition used to tell me that a fully electronic shutter should (could) theoretically move at some significant fraction of the speed of light.

Edit ... Is the process some kind of sequential pixel read ?

maxuci Contributing Member • Posts: 737
Re: How fast is the a7RII silent shutter?

This is great Jim. I love the simulation of the inertia for the EFCS. I wonder if the acceleration of the physical shutter could change over time due to wear or lubricant loss etc.

You don't go into detail about your input function (I did note you said triangle wave below). Is it a super high frequency input (well super high compared to the time frames under investigation)?

JimKasson
OP JimKasson Forum Pro • Posts: 29,577
Re: Faster in APS-C mode!
2

moffatross wrote:

JimKasson wrote:

1/20 second.

I'm surprised, much as when I first read about the limitations for flash sync'ing using EFCS. My intuition used to tell me that a fully electronic shutter should (could) theoretically move at some significant fraction of the speed of light.

Edit ... Is the process some kind of sequential pixel read ?

If there's no global shutter -- and there isn't in the a7RII -- an all-electronic exposure starts with a rolling reset and ends with a rolling read.

So, to answer the question in your edit: yes!

Jim

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JimKasson
OP JimKasson Forum Pro • Posts: 29,577
Re: How fast is the a7RII silent shutter?

maxuci wrote:

This is great Jim. I love the simulation of the inertia for the EFCS.

Note that the engineers didn't bother with that for the silent shutter mode.

I wonder if the acceleration of the physical shutter could change over time due to wear or lubricant loss etc.

LOL!

You don't go into detail about your input function (I did note you said triangle wave below). Is it a super high frequency input (well super high compared to the time frames under investigation)?

It's a triangle wave to make it illuminate the scope face evenly. And yes, it's high enough frequency that one period is smaller than the spot size at the chosen time base setting.

And don't try this with a digital scope; it won't work.

Jim

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Horshack Veteran Member • Posts: 8,533
Re: Faster in APS-C mode!
1

moffatross wrote:

JimKasson wrote:

1/20 second.

I'm surprised, much as when I first read about the limitations for flash sync'ing using EFCS. My intuition used to tell me that a fully electronic shutter should (could) theoretically move at some significant fraction of the speed of light.

Edit ... Is the process some kind of sequential pixel read ?

You can see a visual depiction of this here, which depicts an external flash sync with the RX10M2's fully-electronic shutter, which based on the experiment has a readout speed of approx 1/100.

JimKasson
OP JimKasson Forum Pro • Posts: 29,577
Re: Faster in APS-C mode!

Horshack wrote:

You can see a visual depiction of this here, which depicts an external flash sync with the RX10M2's fully-electronic shutter, which based on the experiment has a readout speed of approx 1/100.

That's a nice technique, too, and doesn't require a 'scope. You won't see the inertia simulation that way, though.

Jim

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Horshack Veteran Member • Posts: 8,533
Re: Faster in APS-C mode!

JimKasson wrote:

Horshack wrote:

You can see a visual depiction of this here, which depicts an external flash sync with the RX10M2's fully-electronic shutter, which based on the experiment has a readout speed of approx 1/100.

That's a nice technique, too, and doesn't require a 'scope. You won't see the inertia simulation that way, though.

Jim

Agreed. Reading the A7rII manual it appears they left out flash support for the SS, same as they did for the A7s (the camera wont even sent a pulse to the hotshoe for non-Sony flashes). Probably because they figured the sync speed was too slow to be useful, although IMO it would still be useful for scenarios where the flash is the primary illuminant and thus shutter speed doesn't matter.

JimKasson
OP JimKasson Forum Pro • Posts: 29,577
Re: Faster in APS-C mode!
1

Horshack wrote:

Agreed. Reading the A7rII manual it appears they left out flash support for the SS, same as they did for the A7s (the camera wont even sent a pulse to the hotshoe for non-Sony flashes). Probably because they figured the sync speed was too slow to be useful, although IMO it would still be useful for scenarios where the flash is the primary illuminant and thus shutter speed doesn't matter.

Remember FP flash bulbs? Maybe we could get 1/12 second ones?

Jim

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moffatross
moffatross Senior Member • Posts: 1,128
Re: Faster in APS-C mode!

JimKasson wrote:

moffatross wrote:

JimKasson wrote:

1/20 second.

I'm surprised, much as when I first read about the limitations for flash sync'ing using EFCS. My intuition used to tell me that a fully electronic shutter should (could) theoretically move at some significant fraction of the speed of light.

Edit ... Is the process some kind of sequential pixel read ?

If there's no global shutter -- and there isn't in the a7RII -- an all-electronic exposure starts with a rolling reset and ends with a rolling read.

So, to answer the question in your edit: yes!

Thanks Am I right in thinking then that any fully electronic shutter speed limitation is mostly about data crunching rather than the physics of moving electrons fast enough (although I guess from your observed rate of change of the electronic shutter that physics may also have some impact) ?

Horshack Veteran Member • Posts: 8,533
Computational comparison to A7s and S35 video calcs
2

Once again, great data Jim! Some calculations vs the A7s and full-sensor sampling for the A7rII's S35 mode:

First, comparing the A7rII's 1/12 readout speed to the A7s's 1/30, it appears the A7rII is a little faster on a pixel-weighed basis:

  • A7rII: 7952x5304 (42,177,408 total pixels)
  • A7s: 4240x2832 (12,007,680 total pixels)
  • A7s has 0.284694592896747 the number of pixels as the A7rII
  • Multiply the A7rII's 1/12 readout speed by the pixel count differential results in 1/42, vs the A7s's 1/30. This assumes readout speed is pixel-count related only vs row or column counts, which is probably not precise but a fun swag nevertheless

Focusing specifically on the A7rII's S35 16:9 mode, which presumably has full-sensor sampling...this mode samples a sensor area covering 5168x2912 (15,049,216 total pixels), based on a stills size for S35 16:9 mode from the A7rII manual. This represents 35.68% of the A7rII's total pixels, which when multiplied by the A7rII's FF 3:2 readout speed of 1/12 comes to 1/33 ...fast enough for full-area S35 sampling at 24fps and 30fps, same as the A7s's FF video modes

One thing I can't get to add up is your 1/20 S35 3:2 SS readout measurement. S35 3:2 has 42.24% the number of pixels as FF 3:2 mode, which means on a pixel-count differential basis the S35 3:2 SS readout speed should be approx 1/28 vs 1/12 for FF 3:2. This might come back to the speed not being precisely based on pixel counts, although the math on that basis does seem to match for the S35 16:9 full-sampling calcs. hmmm....

Horshack Veteran Member • Posts: 8,533
Proof that shutter moves down-to-up on NEX/FE bodies
5

JimKasson wrote:

Since scope traces from left to right, the fact that the top of the diagonal is left of the bottom means that the shutter exposed the top of the image before it exposed the bottom. Since the image is upside down on the sensor, that means that the a7RII’s mechanical shutter must move from the bottom of the camera to the top.

Assuming Sony shares the same shutter orientation on all their NEX/FE bodies, here's a high-speed video I took of the NEX-5N's shutter showing the mechanical shutter moving down to up. This was filmed on RX10M2 @ 960fps:

EFCS vs Mechanical Shutter movements on the Sony NEX-5N (YouTube)

J A C S
J A C S Forum Pro • Posts: 16,901
Re: How fast is the a7RII silent shutter?

JimKasson wrote:

I took a picture:

Consider the bright part of the trace.

Why is there a darker (not black) part on the left in the first place? Is that electronic 1st curtain and a mechanical second?

Horshack Veteran Member • Posts: 8,533
Re: How fast is the a7RII silent shutter?

J A C S wrote:

JimKasson wrote:

I took a picture:

Consider the bright part of the trace.

Why is there a darker (not black) part on the left in the first place? Is that electronic 1st curtain and a mechanical second?

Phosphor ghosting on the scope's screen from the line moving across it left to right.

kelstertx Veteran Member • Posts: 5,245
Re: Faster in APS-C mode!
1

JimKasson wrote:

A few examples of focal plane shutter distortion:

https://www.google.com/search?q=focal+plane+shutter+distortion&tbm=isch&tbo=u&source=univ&sa=X&ved=0CDgQsARqFQoTCIzf0trUn8cCFYgcPgodprIEfw&biw=1366&bih=864

What's not natural about this shot?  LOL

-Kelly

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J A C S
J A C S Forum Pro • Posts: 16,901
Re: How fast is the a7RII silent shutter?
1

Horshack wrote:

J A C S wrote:

JimKasson wrote:

I took a picture:

Consider the bright part of the trace.

Why is there a darker (not black) part on the left in the first place? Is that electronic 1st curtain and a mechanical second?

Phosphor ghosting on the scope's screen from the line moving across it left to right.

Oh, I knew that it was a stupid question but I did not know why!

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