Re: EFCS vs electronic shutter Bokeh (A7CII, A7CR, ZV-E1)
The background:
Full mechanical shutter = both curtains travel in front of the sensor at the same distance = no problems.
Full electronic shutter, so called e-shutter = both curtains travel directly on the sensor = same distance = no problems.
EFCS (Electronic First Curtain Shutter) = first electronic curtain travel on the sensor plane and the second mechanical curtain travel a few millimetre in front of the sensor = not the same distance = can cause problems due to some odd light sneaking in at an angle between the curtains due to the distance difference (there was a good schematic and explanation at DPR long ago that showed this in detail how it happened).
The problem here manifest itself as more nervous bokeh typically, and also chopped of bokeh balls (meaning non round highlight circles). This happens at high shutter speeds (when the shutter only has a slit open that travels over the sensor surface) and with fast wide open lenses. Not otherwise.
In general e-shutters read out row after row top to bottom one row at the time. That process happens on "normal" (non stacked) sensors at around 1/15-1/60 of a second depending on make and model. For moving subjects this means that things can have moved between the first and last line is read out. Even if you shot at 1/8000 since that is the time each line is exposed. Also if you move the camera due to shake or panning you will get the jello effect.
E-shutters on stacked sensors typically reads out between 1/160 and 1/250 which makes less problems with moving subjects. Some reads out several lines at once, so they are reading in chunks. Some can sync with flash also.
One can get banding when one uses EFCS or E-shutter with HSS flash and also with LED-lights even with a stacked sensor in rare cases.
In even rarer cases banding and jello effects can also happen with mechanical shutters. They typically travel from top to bottom at the flash sync speed, often 1/250 but some cameras have lower like 1/160 and in the analog days 1/60 wasn't unusual. And before that they were even slower, there are some really cool shots available online with racing cars shot about 100 years ago which on the pictures have oval wheels and leaning telephone poles in the background due to the panning.
And before you say, but how can the first curtain of a normal slow readout sensor in EFCS shutter mode keep up with the mechanical rear curtain that does 1/250. And the answer is that it is the read out (saving) in e-shutters that takes time (usually 1/15-1/60 if non stacked). Opening the first electronic curtain on a normal sensor can be done as fast as the rear curtain can do its travel (1/160-1/250).
As for how different aperture / shutter speeds combos bokeh distortion looks, there used to be some examples found if one google it.
The day we get global shutters (all pixels read out at the same time) we will get rid of these problems.
Sep 19, 2023 at 06:05 PM
Previous versions of lattesweden's message #16346067 « EFCS vs electronic shutter Bokeh (A7CII, A7CR, ZV-E1) »
