Silent shutter mode refers to a full electronic shutter being used to take the photo on a digital camera and the mechanical shutter mechanism being disabled.
Why use silent shutter mode?
- this mode is required for shooting movies on digital cameras
- it allows silent shooting which may be critical in low noise environments such as a classical music concert, or wedding reception.
- it allows faster burst rates (eg. 18fps with C-AF and 60fps with S-AF on the Olympus OM-D E-M1 II)
- it avoids excessive use of the mechanical shutter which has a limited life – most are rated at around 150,000 shots
- it avoids shutter shock which blurs all images at shutter speeds 1/4 sec to 1/200th sec unless you use electronic first curtain shutter mode (EFCS) which is a partial electronic shutter and available on most new cameras
What are the problems with using a silent shutter mode?
- your subject can’t hear when you take the shot
- you may get banding when shooting in artificial light at faster shutter speeds
- you may get distorted / slanted lines on moving subjects or if you are panning the camera – this is called rolling shutter.
- you may have to use very slow shutter speeds when using flash otherwise only part of the image will be illuminated by the flash
Most of the problems are related to slow sensor readouts
How does a slow sensor readout cause rolling shutter?
- a digital camera sensor must read data from each row of photosites on the sensor sequentially up or down the sensor and thus each row “sees” a potentially different scene in time
- thus if one shoots a bus moving across the scene, the top of the bus will be imaged to one side of the image while the bottom of the bus will be imaged towards the other side of the image creating a slanting line of all the vertical lines of the bus.
- the faster the sensor read out occurs, the more vertical is the final line in the image and the less “rolling shutter”
- dpreview has a nice explanation here.
What are the determinants of sensor readout speed?
- sensor readout time is determined by:
- photosite size – larger photosites take longer to read hence a 20mp full frame sensor will be slower and with more rolling shutter than a 20mp cropped sensor camera such as Micro Four Thirds, all else being equal.
- bit rates – a 14 bit read out takes longer than 12 bit as there is more data to collect hence some cameras revert to 12bit mode in silent shooting
- number of megapixels – the more rows to read out, the longer it will take, this is part of the reason why high resolution full frame cameras (eg. 45mp or more) do not make great video cameras – everything is a compromise
- engineering – some cameras (eg. Panasonic GH5) are designed to slow down the read out rate at higher ISOs to improve image noise
- sensor design – stacked sensors generally have faster read out rates (eg. Sony a9), but these are much more complex and expensive to make
Which cameras have moderately fast sensor readouts and minimal rolling shutter?
To put this in perspective analog film movie cameras which have a rotating shutter mechanism have the equivalent of sensor readout of 5msec or 1/200th shutter speed, and this is also a similar amount when shooting with film or digital cameras in mechanical shutter mode.
Digital cameras with similar rolling shutter capabilities in electronic mode include the Arri Alexa Mini video camera, the Canon C300 II video camera, and uniquely in the still camera market, the Sony a9 with its stacked sensor design.
Cropped sensor cameras such as the Fuji XT-3, Panasonic GH-5, Olympus OM-D E-M1X and Olympus OM-D E-M1 mark II all have minimal rolling shutter thanks to a sensor read out of 20msec or faster (note the GH5 has a much slower sensor read out if shot above ISO 800).
Which cameras have slow sensor readouts and thus problematic rolling shutter?
Apart from the Sony a9, ALL full frame and medium format cameras have relatively SLOW sensor readout times of around 30msec or slower, with the Fujifilm GXF 50S medium format camera coming in at a whopping 250msec or incredibly slow 1/4 sec, the Sony a7RIII at 70msec or 1/15thsec, the Nikon Z7 and Nikon D850 at 64msec or 1/15thsec (although it can get to 1/40th sec in cropped mode), Nikon Z6 at 44msec or 1/22nd sec, Sony a7III at around 1/15th-1/30th sec.
Older cameras have slower read outs such as the Olympus OM-D E-M1 mark I which had a read out time of 77msec or 1/13th sec.
I would avoid using silent shutter mode on these cameras for sports!
How can you measure your camera’s sensor read out time?
There are several ways of measuring this and perhaps this creates the variances on the measurements people quote on the internet for each camera.
The easy way is to set the camera in silent shutter mode and ensure the camera is set to allow flash in silent mode (this may be a menu setting), then take shots at different shutter speeds and the fastest shutter speed that has the full image illuminated by the flash is the read out.
Some people measure the degree of distortion of rotating vertical lines, and others use oscilloscopes.
How will this issue be fixed in the future?
In the short term, perhaps stacked sensor technologies will be more utilised as with the Sony a9 but this is complex and expensive.
In the medium term (perhaps 5-10 years), we will see sensors with “global read outs” (ie. sensor read out time difference from top to bottom of sensor will be zero) developed which address the current problems of complexity, image noise and cost. These will be game changers as these will not only eradicate rolling shutter, artificial light banding but allow flash sync at any shutter speed and be far more effective than the very limiting current high speed shutter (HSS or Super FP) modes on current cameras.
For more details, see my wiki page for links and more resources.