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You are here: Home / The Last Word / a7RII read noise with EFCS on and off, plus silent, continuous

a7RII read noise with EFCS on and off, plus silent, continuous

August 6, 2015 JimK 25 Comments

I have seen claims that the a7RII has lower precision with EFCS on than it does with it off. That makes no sense to me, and the a7, a7S, and a7II don’t do that.  Since it’s pretty easy to check, I ran read noise curves both ways:

a7rii rn efcs off

a7rii rn efcs on

The curves are virtually identical.

While I was at it, I looked at the read noise with the silent shutter on:

a7rii rn silent

Silent shutter does indeed increase read noise.

So does continuous shutter:

a7rii rn cont iso

If you’re more comfortable looking at EDR curves, here’s the continuous shutter data that way:

a7rii edr cont iso

We can see what’s going on with the precision by looking at some histograms.

Regular shutter:

iso 500 noisy

Every other bit bucket is depopulated, meaning that there are thirteen bits of precision.

Silent shutter:

iso 500 silent

Only a quarter of the buckets are occupied, meaning that there are twelve bits of precision. Not only that, the noise level is higher.

Looking at continuous mode, we see something similar, but the noise levels are better, as shown by the curves.

iso 500 cont

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Comments

  1. David Bukach says

    August 8, 2015 at 9:50 am

    Very interesting that electronic shutter and continuous shooting has differing resolution. Do you know what the sensor read speed is for the electronic shutter mode? I need silent shooting for my photographic work on film sets, so readout speed is a key feature (and I can’t find the information anywhere). I know you have done tests with other cameras, so any help would be great.

    Reply
    • Jim says

      August 8, 2015 at 9:55 am

      Silent shutter read speed on the a7S is 1/30 second:

      http://blog.kasson.com/?p=6450

      I would expect about the same for the a7RII, but I haven’t tested it. I could end up being surprised.

      Jim

      Reply
  2. David says

    August 8, 2015 at 11:41 am

    Thank you for doing the tests and showing the results so clearly.

    I’m mystified. Why would Sony let this happen ?
    Assuming its not an intentional design “feature” why would they leave this hardware bug/problem in a production camera ?

    What do you think could be causing it ?

    Reply
    • Jim says

      August 8, 2015 at 12:02 pm

      I don’t consider any of this behavior to be the result of an error. I beleive the camera works as designed for what I’m reporting here.

      I think there are probably speed/cost tradeoffs at the root of all these little quirks, except for the bulb mode spatial filtering and bit-depth loss, which, frankly, mystifies me.

      Jim

      Reply
  3. Jonathan Stewart says

    August 8, 2015 at 12:30 pm

    In experimenting with silent shutter in my A7R2 last night, I got striped artifacting in artificial light. My guess is the sensor read was out of phase with the lighting (incandescent – so it probably had to do with the ac current), and it led to these ugly lines in my photos. As an engineer, what do you think?

    Reply
    • Jim says

      August 8, 2015 at 12:45 pm

      That’s typical with a 1/30 second scan time, which is probably what the a7RII does (I have yet to test it). I’m surprised that you saw it with incandescent lights; usually the thermal time constant of the filament is long enough to prevent this.

      Reply
      • Jonathan Stewart says

        August 8, 2015 at 1:55 pm

        See the sample image I linked to. They were incandescent, which leads me to think it may have had something to do with the current cycling.

        Reply
        • Jim says

          August 8, 2015 at 2:13 pm

          Current cycling? I don’t understand.

          Reply
          • Jonathan Stewart says

            August 8, 2015 at 2:55 pm

            Sorry. I’m not an engineer. But with alternating current, the electricity cycles, right? And wouldn’t this cycling manifest itself by imperceptible on/off cycles that might be picked up by a sensor taking samples not in phase with these cycles? Like I said, I’m no engineer, so I may be way off here.

            Reply
            • Jim says

              August 8, 2015 at 3:50 pm

              Th ac cycles at 50 or 60 Hz. So most lights are modulated at 100 or 120 Hz. The bands appear to be faster than that.

              Reply
  4. Jonathan Stewart says

    August 8, 2015 at 12:31 pm

    Here’s the specific photo. After I turned off silent shutter, the effect disappeared.

    http://www.jonathanstewartphotos.com/GearReviews/A7R2-Samples/n-TWgR7p/i-3GzJSsW/A

    Reply
    • Jim says

      August 8, 2015 at 12:48 pm

      I count at least ten bands from top to bottom. That’s too fast for ac mains fluctuations, unless the travel time is a lot slower than I think it is.

      Jim

      Reply
      • Jonathan Stewart says

        August 8, 2015 at 1:56 pm

        Do you have another theory?

        Reply
  5. David Bukach says

    August 10, 2015 at 12:44 pm

    The bands are based on the frequency of the light (as far as I understand). Tests on some micro 4/3 camera electronic shutters are seen here, and the banding is used to determine the length of time the sensor takes to scan the entire image:

    http://m43photo.blogspot.ca/2014/06/gh4-shutters.html

    So, if the light is 100hz and there are 10 bands then the sensor scan speed is roughly 10/100 or 1/10 of a second. You can occasionally get this kind of flicker effect on cinema camera as they are shooting at shutter speeds slower than the frequency of the lights ie. 1/24.

    Its something I have looked into as I need a silent camera to work on film sets (I am an on set photographer) that also has a good sensor scan speed that avoids stretching or jello effects on moving objects or when I move the camera. The a7s was a big deal as it was a 1/30 second scan time which was pretty good – just the resolution is too low for some of my clients. I did use a fuji x-t1 in electronic shutter mode, but it had issues with movement as it had a 1/15 scan time. Been playing with a Nikon 1 v2 which scans at a speed of 1/60 which seems to eliminate these problems in almost all circumstances – but its at a price as it is only a 1″ sensor.

    I was hoping that the a7r ii would be the camera for me, but it looks like the scan time is longer in order to be able to scan the 42mp sensor – not surprising, but too bad.

    So, I think that is why – but feel free to correct me!

    Reply
    • Jim says

      August 10, 2015 at 3:19 pm

      So, if the light is 100hz and there are 10 bands then the sensor scan speed is roughly 10/100 or 1/10 of a second.

      How right you are!

      http://blog.kasson.com/?p=11258

      Jim

      Reply
      • David Bukach says

        August 10, 2015 at 6:50 pm

        Thank you, thank you, thank you for running a further test! This is very helpful to know. I guess I will wait patiently for the sensor scan performance of the eventual A7s ii and give the A7r ii a pass for silent shooting during my film industry work – can’t quite ditch the sound proof housings yet!

        Reply
  6. Joel says

    August 10, 2015 at 12:48 pm

    That may not be an incandescent bulb but an LED filament bulb. https://en.wikipedia.org/wiki/LED_Filament

    Reply
    • Jim says

      August 10, 2015 at 12:56 pm

      Amazing. I had no idea those existed.

      Reply
      • Joel says

        August 10, 2015 at 1:05 pm

        Could be operating in PWM dimming mode. The risetime of the LED itself is nanoseconds but the phosphors have a exponential decay, this matches with the stripes having a bright edge and then fading as you go down.

        Reply
        • Jim says

          August 10, 2015 at 1:23 pm

          Good catch, Joel.

          Reply
          • Joel says

            August 10, 2015 at 1:29 pm

            http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/poplawski_dimming_lightfair2012.pdf has some waveforms of LED dimming. Can be quite complicated.

            Reply
            • Jim says

              August 10, 2015 at 1:50 pm

              Oh, my. Thanks for that.

              Jim

              Reply
  7. David Bukach says

    August 10, 2015 at 1:04 pm

    So it might actually be 150-200 hz bulb (or more?) – so the scan speed is closer to 1/15 or 1/20th? Man, I was just starting to be happy with my decision not to have to buy the camera – if its some crazy high hz bulb then I am now still confused!

    Reply

Trackbacks

  1. What’s the base ISO of the Sony a7RII? | The Last Word says:
    August 28, 2015 at 9:05 am

    […] looking at the read noise curves here, http://blog.kasson.com/?p=11142 you can see that the conversion gain change is a little over one stop. Actually, you can get the […]

    Reply
  2. Cruising with the Sony a7RII – summary | The Last Word says:
    September 27, 2015 at 7:36 am

    […] The two speed ISOlessness. Having the increase in conversion gain occurring at ISO 640 is a great thing, allowing almost all photographs to be exposed using the camera set to one of two ISO levels. This simultaneously provides simplicity and high-quality. […]

    Reply

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