Edymagno wrote:
If the Electronic First Curtain works by turning on and off each pixel and row after row, why is it necessary a second mechanical shutter after the shot?
Wouldn't just be enough to stop the ON-OFF sequence?
If you play at home by turning the lights on/off rapidly when people moving or dancing, you get a stroboscopic effect. In fact what you see are still frames.
Tia
Ed
The sensor is measuring photon activity, kind of like a charge.
Before you turn it off, you have to read out how much charge was collected during the exposure.
Catch is, it takes much longer to read out the sensor array than the exposure time itself.
During the readout, if left ON, the sensor would keep collecting charge, or over-exposing.
If you turn it OFF again, you'd loose the image (i.e. the stored charge). There is no electronic way that would change the sensor into a non-collecting state. Therefor, you are left with the handicap of having to read out each sensor in parallel when the exposure closes - that is, you need an analog to digital convertor circuit for each sensor. Adding such a A-D circuit limits the effective sensor area and limits the maximum amount of photons that can be collected (or ISO sensitivity).
Also, cost-wise, it is far more economical to read out the sensor array in rows or columns - this brings the IC complexity down exponentially. For this, the only (simple) remedy is the mechanical shutter which closes the exposure and prohibits additional charge from being collected.
The ON works basically because you 'reset' the charge, and re-start counting/collecting.
I don't ever foresee an electronic second curtain in high end DSLR or mirror less cameras - the added logic would degrade the sensors ability to store charge and limits its DR.
camb.color
In Point&Shoot cameras, they do away with the mechanical second curtain, by doing just that: adding logic to convert the analog charge to digital values at the end of the exposure. This added logic makes the sensor more clompex, and hence more expensive (which is offset by the smaller sensors used in P&S cameras), but it also limits the sensor from reaching its maximum optimum performance - contributing in a way to limiting ISO values on small sensors as well.
In a P&S camera, the mechanical shutter is an unwanted object - it makes the camera larger and more cumbersome to use, whereas the A-D readout is cost wise a better trade-off, and the compromise seems well accepted.
In APS-C and FF cameras, the market wants the opposite - get the best sensor performance possible, and use a mechanical shutter to reach this. With the added cost and bulk of the mechanical shutter, it is still a positive trade-off.
Note, there are several other techniques, such as focal plane shutter (FPS) and even electronic (on sensor) but mechanical 'levers' that interrupt exposure - all these can still be seen as a mechanical solution of sorts.
