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metering precision and flicker from LED


geotrupede
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Hi all,  I have noticed evident flicker in the live view, absolutely expected. Nothing odd there.

BUT as live view is the way the camera measures light, the measurement also fluctuates, if light does so.  Spot reading the one most affected.

Evidence of this was 1 stop or so up and down in the meter.  nothing of an issue given the monstrous latitude of exposure, but still, not as precise as was expecting.


All good with daylight, far from windmills

😉

G.

 

 

 

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Posted (edited)

Do you mean that the LV flickers because the scene is illuminated by LEDs without flicker-free circuitry? In which case the exposure meter is doing exactly what it should, responding to the (flickering) light levels. All we can do is be aware of the effect and the cause; not much else one can do about it.

Edited by LocalHero1953
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The old exposure meter was so slow that it measured the average perceived by human eyes; that was due to a relatively long integration time.

the new system is capable of measuring at higher frequency, by virtue of slowness in the readout of a single frame/image (note, my unproven suspicion). 

P e r s o n a l l y,  I'd rather get a more stable readout /  longer integration time for my type of photography.

The bouncing exposure meter effect, was not that useful to me as I could not figure out if I had to expose to the higher or lower or average value, or in fact what was going on...  until I Live Viewed the stripy effect, and eureka!

Never had this 'issue' with the previous Ms, so was a bit surprised to find out. I also did not notice it on the SL2s, but maybe because I look less the meter and more the EVF for exposure 😜 

G>

 

 

PS

Typically, the flicker on the LED systems happens due to pulse width modulation, in practical terms the light is on/off at a certain (and manufacturer dependent) frequency to create the apparent effect of a dimmed output. The eyes read an average over time.

A slow sensor readout happens to capture rows of pixel of darkness and light within a single frame. When the on/off of the LED is happening.

A simple trick to measure the flicker frequency is to set shutter speed to 1/10th, take an f16 exposure of the LED light source (at low ISO), directly pointing to it, and dragging the camera from one side of the frame to the other. the resulting image will show a number of dots, the number of dots multiplied by ten is the number of on/off flashes within a second, which happens to be the frequency of the flicker for that light. 

 

 

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