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p.1 #9 · p.1 #9 · "Sony’s ‘Shutter Speed Fine-Tuning’ Feature Totally Eliminates LED Flicker" | |
osv2 wrote:
sports dslrs automatically sense and change the timing of the shutter actuation to fight flicker, the a9ii does that in mechanical shutter mode as well... it's effective in many traditional lighting scenarios, but also very limited in what frequencies it can detect:
"Flicker at a frequency other than 100 Hz or 120 Hz cannot be detected." https://support.usa.canon.com/kb/index?page=content&id=ART168687&actp=LIST
this a9ii electronic shutter tweak changes the shutter speed, not the timing, so it's a different approach, probably better in terms of light sources that have radically different flicker frequencies, like dimmed led for instance.
https://www.davidsatz.com/aboutflicker_en.html
The reason bands are visible in an electronic shutter exposure is due to the light cycling (bright->dark->bright) at different integral rates across the full-sensor readout. For example, if we examine Sony's A9II flicker-eliminating sample video we can observe approximately 12 visible bands of light in the LV feed at the initial shutter speed of 1/1024.6 (0.9759ms). Measuring a screen grab more closely in Photoshop I came up with about 11.6 bands. The A9/A9II's full-sensor readout rate is approximately 1/160 (6.25ms). If we see 11.6 visible bands this means the full-sensor readout captured 11.6 cycles of the light, so we can derive the frequency of the light illuminating the scene by dividing 1/160 (6.25ms) by 11.6, which gives us 1856Hz (0.5387ms per light cycle), probably PWM LED lighting. The bands disappear in the video when the shutter speed is changed to 1/843.2 (1.1859ms), which is approximately 21.51% slower than the initial shutter speed at the start of the video. That brings the exposure of each row to approximately 1/2 rate of the light's cycle (0.5387ms per light cycle * 2 = 1.0774ms, ie each row captures two full cycles of light, which will eliminate the gradations of light bands across all rows). My numbers don't precisely match up since the 1/160 readout rate is an approximation as is the number of bands counted. Based on the revised A9II manual's High Frequency Flicker Section, the new firmware gives the user very precise control over the shutter speed, which should allow the user to find one that's a near-even multiple of most lighting sources.
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