Electronic shutter and LED lighting

[vikasmg]

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I still haven't got my head around exactly why this happens - probably because I have not spent the time to read up on it - but yesterday I had the clearest demonstration of the problem of using LED lights with the electronic shutter.  For some reason the setting was "always on" (I don't understand why!) when I tool the camera out to shoot some pictures of an architectural model lit with LED lights.  Here's what happened:

 

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Suspecting the problem I drilled into the menu (made me miss the Leica T style menus) and turned the electronic shutter off.  The picture has other problems but the stripes problem was solved:

 

 

 

- Vikas

[lct]

My electronic shutter is "Always On" as well but i disable it when there are some LEDs around. I have just set up a user profile for that. 

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[jaapv]

Not surprising

LED light pulses with the frequency of the current. So do filament bulbs, but as they will keep glowing during the pulse you don't notice. As LED switches much faster it becomes noticeable.

That means you will get stroboscopic effects using an electronic shutter in LED lighting.

[scott kirkpatrick]

From Vikas' picture, it appears that the AC-powered LEDs pulse at 2x the frequency of the current, either 100 Hz or 120 Hz, depending on the country.  That's just like flourescent bulbs, and it shows that the time taken for the CL to capture and unload its electronic shutter image is pretty slow -- around 1/10 sec. or 1/(max continuous firing rate).  But with fluorescents in normal use, the presence of multiple sources seems to fill things in, and there may be some persistence to smooth the pulses, so test shots at different shutter speeds sometimes show no artifacts at all at some speeds.

 

Vikas, what was your light source, and did you try several shutter speeds?

[vikasmg]

My electronic shutter is "Always On" as well but i disable it when there are some LEDs around. I have just set up a user profile for that. 

 

Interesting.  Where do you find the electronic shutter useful?  I mean in what situations do you need the higher shutter speeds?

 

- Vikas

[vikasmg]

From Vikas' picture, it appears that the AC-powered LEDs pulse at 2x the frequency of the current, either 100 Hz or 120 Hz, depending on the country.  That's just like flourescent bulbs, and it shows that the time taken for the CL to capture and unload its electronic shutter image is pretty slow -- around 1/10 sec. or 1/(max continuous firing rate).  But with fluorescents in normal use, the presence of multiple sources seems to fill things in, and there may be some persistence to smooth the pulses, so test shots at different shutter speeds sometimes show no artifacts at all at some speeds.

 

Vikas, what was your light source, and did you try several shutter speeds?

The light source was mainly the LEDs lighting the model itself.  The darker bands still seem to have visible elements, though darker and I assume this is from the ambient light in the room - mostly from fluorescents.  I took a couple of pictures but they are very similar and both at 1/1250th of a second.  After I switched to a mechanical shutter the speed went down to 1/640 to 1/500th.

 

The LEDs light sources are mainly within the case of the building, emerging from the bases of the buildings, within the two featured buildings, in the modelled street lamps' and some for some reason at the edges of the street kerbs (or curbs).

 

- Vikas

[LocalHero1953]

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From Vikas' picture, it appears that the AC-powered LEDs pulse at 2x the frequency of the current, either 100 Hz or 120 Hz, depending on the country.  That's just like flourescent bulbs, and it shows that the time taken for the CL to capture and unload its electronic shutter image is pretty slow -- around 1/10 sec. or 1/(max continuous firing rate).  But with fluorescents in normal use, the presence of multiple sources seems to fill things in, and there may be some persistence to smooth the pulses, so test shots at different shutter speeds sometimes show no artifacts at all at some speeds.

 

Vikas, what was your light source, and did you try several shutter speeds?

Arithmetic check: that looks to me like 5 cycles on the image, which implies 1/20s or 1/24s. That is similar to what I estimated for the SL, based on a far less precise experiment. That would be similar to typical read-out speeds of other mainstream cameras (i.e. not cutting edge, but not exceptionally slow), aside from the faster shutters that Sony has been producing recently.

 

Edit: Jim Kasson measured the A7Rii as 1/15s and the A7Riii as 1/30s

He measured the A9 at 1/150s

Edited March 3, 2018 by LocalHero1953

[scott kirkpatrick]

Arithmetic check: that looks to me like 5 cycles on the image, which implies 1/20s or 1/24s. That is similar to what I estimated for the SL, based on a far less precise experiment.

Right, I counted both light and dark bands, but the light bands (of which there seem to be 5 plus 6 dark bands) are when the light is flashing on.  LEDs care about the sign of the voltage applied, while flourescents can light at either the + or the - maximum AC voltage, I believe.  So you get twice the AC frequency with flourescents.  Since LEDs are DC devices, and certainly don't run at 110 or 220 volts, the type of voltage conversion circuit used to drive them will affect the amount of high frequency signal and not all LEDs will behave as in Vikas' example.  (Certainly my battery-powered FotoDiox unit will not.)

[LocalHero1953]

Right, I counted both light and dark bands, but the light bands (of which there seem to be 5 plus 6 dark bands) are when the light is flashing on.  LEDs care about the sign of the voltage applied, while flourescents can light at either the + or the - maximum AC voltage, I believe.  So you get twice the AC frequency with flourescents.  Since LEDs are DC devices, and certainly don't run at 110 or 220 volts, the type of voltage conversion circuit used to drive them will affect the amount of high frequency signal and not all LEDs will behave as in Vikas' example.  (Certainly my battery-powered FotoDiox unit will not.)

I was assuming that small simple LEDs run off a full wave rectifier bridge, with nothing to smooth out the signal - hence they fluctuate at twice the mains frequency. I'm not an expert, though, so I'm happy to be told I'm wrong.

[scott kirkpatrick]

I was assuming that small simple LEDs run off a full wave rectifier bridge, with nothing to smooth out the signal - hence they fluctuate at twice the mains frequency. I'm not an expert, though, so I'm happy to be told I'm wrong.

I'm not expert, either.  At most I can read a Wikpedia article or a spec sheet.  I've seen examples where the banding effect with an always-on electronic shutter is obvious at 1/125 sec and gone at 1/250 or 1/60, so it pays to experiment.  If I find the time, I will read up on this some more.  I think there are unknown behaviors in both shutter and light source to be figured out.

Edited March 4, 2018 by scott kirkpatrick