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| Panasonic LX100 |
Significance for cameras and photography
Sony recently released two cameras each fitted with the new “one inch” (15.9mm diagonal) RS sensor which features both “back side illuminated” (BSI ) [presumably the “R” designation stands for “reverse”] and “stacked” architecture.
The cameras are the RX100 Mk4 and the RX10 Mk2.
In due course this sensor will find its way into cameras from other brands but for the moment it is exclusive to Sony.
The previous generation Sony 15.9mm sensor, with BSI but not stacked architecture can be found on the Sony RX100 Mk3, Sony RX10 (original), Panasonic FZ1000, Canon G3X, Canon G7X and probably the latest Nikon 1 series cameras.
15.9mm is currently the largest RS sensor size available. RS architecture can also be found in smaller Sony sensors.
The importance of the new sensors arises from their greatly increased data processing speed.
I don’t pretend to understand the technology but the possibilities arising from the increased speed may be of great interest to those of us who buy and use cameras.
In a nutshell I see RS sensors as the key technology which will allow camera makers to phase out the flipping mirror DSLR design (and the Sony fixed mirror SLT) and move to an all mirrorless product lineup both for interchangeable lens (MILC) and fixed lens (FZLC) types. Sony certainly appears to be headed that way.
A bit of history Early MILCs had some advantages over existing DSLR types, such as more accurate single AF, seamless segue from viewfinder to monitor, ability to place the active AF area anywhere and smaller body size.
But there were disadvantages.
* Single shot autofocus on the early MILCs was a bit slow. This was soon rectified with new direct drive focussing systems in lenses.
* Some MILCs which use focal plane mechanical shutters suffer from a phenomenon which I call shutter shock. This is caused by the close>open>close>open action of a standard MILC shutter.
Methods of dealing with this problem include
# Global Shutter. There is no mechanical shutter at all. Exposure start and stop are controlled on sensor. All the captured data for each exposure is downloaded off the sensor simultaneously and more or less instantaneously. This is shutter nirvana. I believe some video cameras have this feature but no still cameras. Yet.
# Electronic exposure commencement, a.k.a. Electronic First (shutter) Curtain (EFC). This removes the need for the initial close>open shutter action which is the main cause of the shutter shock. Some cameras enable this, some do not. Some cameras, for instance M43 models from Panasonic could greatly benefit from EFC but do not offer it while models from Olympus do.
# Electronic Shutter. The mechanical shutter is not used. Exposure is by scanning down the sensor. With standard sensors this takes around 1/10 -1/15 second. This avoids shutter shock but introduces its own problems.
These include banding in fluorescent and other types of light, shutter speeds longer than 1 second are not available, inability to synchronise flash, distortion of moving subjects (rolling shutter effect) and reduced bit rate capture leading to increased dark tone noise and therefore reduced dynamic range.
From early reports on user forums it appears the new RS sensors offer a substantial increase in scanning speed (Sony claims “more than 5x faster readout of image data”) with each exposure scan taking about 1/100 second at the normal bit rate.
If this is so it will make electronic shutters much more effective than is presently the case, with fewer adverse effects.
This leaves one area where high end DSLRs could outperform Mirrorless cameras, namely
Sport/action The two key functions here are:
* Viewfinder blackout times and
* predictive autofocus
I was reading through the specifications for the RX10(2) on the Sony website yesterday. Sony rightly emphasises the impressive new video capabilities of the camera.
But then I saw this little note about stills photography: “Up to 14 fps continuous shooting without blackout”.
If that is true and does not come with some kind of nasty adverse effect it is very big news indeed.
It means that in one of the two key functions for sport/action work mirrorless cameras may be able to outperform DSLRs with a mirror.
Last but by no means least, we have predictive autofocus.
Mirrorless cameras focus right on the sensor with contrast detect or phase detect operation or both.
DSLRs use a separate PDAF module at the bottom of the camera. Until now this has for various technical reasons which I do not pretend to fully understand, been faster and more effective for predictive AF.
But to the extent that data processing speed can influence the process the new RS sensors should deliver better predictive AF than we have previously seen with mirrorless cameras.
Summary Sony is not claiming much in the way of improved image quality from the new RS sensors. But their greatly increased speed of operation may lead to a change in the types of cameras we use and the functions of which they are capable.
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