Flash and rolling shutter
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Flash and rolling shutter

The obvious challenge of basing a camera around an electronic shutter is that most sensors suitable for high-end photography take some time to read out their data, which limits the maximum speed of their electronic shutter mode.

This has two main consequences: firstly it leaves the risk of rolling shutter distortion if your subject moves as the sensor is being read (this also presents a challenge under artificial light sources, where the lights become brighter and darker during the exposure, leaving dark bands across the image).

The second issue is that it significantly limits the ability to use the camera with flash (if the sensor takes a long time to read-out, you can only fully expose the sensor at long exposure times). So, although Sigma showed the fp with an external flash mounted, it says the maximum sync speed is 1/30 seconds (this drops to 1/15th in 14-bit Raw mode).

In announcing the camera's development, Sigma CEO Kazuto Yamaki acknowledged the rolling shutter effect but said 'the sensor used has a very fast reading speed. It is able to shoot without major problems in most shooting scenes.'