Why don't they make all DSLRs with an electronic shutter? Is it technically possible?
Surely this would allow easier syncing with flashes (rather than the usual 1/200s or 1/250s max).
I could even imagine a special RAW format that basically recorded all data from the CCD for, say, a second and then in software you could retrospectively shorten that time window. eg. only use data recorded in the first 1/100h of a second...
Or am I being stupid?
Sounds nice but apparently there are currently some technical limitations:
An electronic shutter requires the sensor to be equipped with what is commonly called "snap shutter" circuitry. Basically, this is a second set of diodes, as big as the light gathering photodiodes, but shielded under a dark cover, and some additional switches. To shoot, the photodiodes are cleared of charge, exposure starts, and at the end of exposure, the charge in the diodes is transferred over to the shielded storage part of the cell. The cell is already full of stuff, so the only way to make space for this extra circuitry is to cut the size of the photodiode in half. Which cuts dynamic range and low light, high ISO performance.
Source: Joseph Wisniewski
Some key notes...
Cameras, typically smaller point-and-shoot cameras, that use no mechanical shutters typically use an interline transfer sensor. An interline transfer sensor dedicates a portion of each pixel to store the charge for that pixel. The added electronics necessary to be able to store the charge for each pixel reduces the fill factor of the pixel, in turn reducing it's ability to capture light since a portion of each pixel is not light sensitive.
Interline transfer sensor's typically have higher noise levels and lower sensitivity than the full frame sensor's used in high end digital SLR's.
So, basically, the electronics required for an electronic shutter result in compromised image quality.
The obvious bottom line is about CCD sensors. CCD sensors can be used as shutters. CCD has to be disabled each frame to transfer the image out of it anyway, so they can simply time the enabled time as a shutter. Inexpensive cameras (compacts and camcorders, and less expensive DSLR too, back in the older days) still use CCD sensors for the free shutter. These have a cheap mechanical shutter too, to cover the sensor and keep light off of it, used for slow shutter speeds, but faster, has to be left open so the electronic sensor shutter can time it. The downside is the light is still on the sensor when disabled, which can cause blooming.
But the DSLR use CMOS sensors now, better, but more complex, much more issue to disable and reenable them (very slow to do). The first Nikon 1 cameras (mirrorless, NOT DSLR) were CMOS sensors, but had a choice, one model used sensor as a shutter, but its flash sync speed was only 1/60 second. Or a second model with more expensive regular focal plane shutter, with 1/250 second sync. Sync speed is related to shutter operation time, and CMOS is just too complex and slow. Compact users tend not to be concerned with flash sync speed.
The focal plane shutter is technically a much better shutter, but has disadvantages of expense, and of limiting flash sync speed currently to around 1/200 or 1/250 second. Just how life is.
