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Does mechanical shutter on A7CR or A7CII eliminate LED banding?

dclark
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p.2 #1 · p.2 #1 · Does mechanical shutter on A7CR or A7CII eliminate LED banding?

@tschopp, Yes, I did look at the article referenced. Unfortunately is it pretty thin on information so it is speculation what may be the cause of the observations.

In response to the question does switching to mechanical shutter eliminate banding I think the answer is no, but it may well be that the banding will drop so low that it's not noticeable. I will try to explain my answer. First let me note that the Sony reference provided by Steve Spencer has some excellent graphics that help to understand this issue. You need to expand the explanations to see them. I have copied them below.

The first graph shows an example of pulsed light and the shutter curtains traverse the sensor height in the time of 3 pulses. If the light pulses are 1/120 sec, that means the shutter scan time is 1/40 sec, which is typical of a slow electronic shutter, but some cameras are much slower. The large the angle the slower the shutter curtain speed (electronic or mechanical). The width of the band is proportional to the shutter speed. The narrower the band the faster the shutter speed. Again if we assume the light pulse rate is 120/sec, the shutter speed looks like it is ~1/240 sec. So as the shutter slit traverses the sensor it goes in and out of sync with the light pulses and banding occurs. The slower the shutter curtain speed, the more bands are seen. If the shutter curtain speed were to increase so the scan time drops from ~1/40 to ~1/400 sec, it would be very nearly vertical and the change in illumination would be very little. In this case it would start out dark and, although it would brighten a bit, it will stay very dark. The change from ~1/40 sec to ~1/400 sec would be what might occur moving from electronic shutter to mechanical shutter. So in this case the answer to the question you pose is a qualified yes. Banding would not be seen but the unfortunate timing is such that very little light is gathered. The next frame might be better, depending on the random alignment of the open shutter with the light pulses. If the camera has the capability to detect the pulses and center the light pulses in the open shutter, the illumination would be high and there may be a slight non uniformity at the top and bottom of the image. If the camera has a fast electronic shutter, the benefit of switching to mechanical shutter may be very limited. A global shutter would be the limiting case of a vertical band.

Looking at the flash sync speed for the A7CR and the A7CII I see it is only 1/160 sec, which in not that fast. I don't see any data on the electronic shutter, but snapsy's data on the A7C is 1/16 sec. That is a 10X factor which means the banding should be considerably less, but the since the sync speed is about 2X slower than other cameras the residual banding (non-uniformity) will be more noticeable.

The second chart shows the case were the shutter speed is adjusted to be an integral number of pulses, in this case 1. In that case it does not matter how slow the shutter curtains are or how well it is synchronized with the pulses, it always gets one pulse of illumination. A slow shutter curtain speed does not result in banding. So if the camera has the capability to carefully adjust the shutter speed to equal an integer number of pulses the slope (i.e. the shutter curtain speed) does not matter. But the flatter the slope the more precisely the shutter speed needs to be set.

https://www.sony.com/electronics/support/articles/00122281

https://www.sony.com/electronics/support/articles/00122281

Edited on Sep 05, 2024 at 07:05 AM · View previous versions

Sep 04, 2024 at 11:35 PM

Juha Kannisto
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p.2 #2 · p.2 #2 · Does mechanical shutter on A7CR or A7CII eliminate LED banding?

Steve Spencer wrote:
...

Note the A7C series only have anti-flicker and not the variable shutter feature. The A9 I and II and A1 have the variable shutter feature. So camera type really does matter and there are times when the A7C series will not be able to avoid banding. Your best bet is to first try adjusting shutter speed to 1/60 or 1/120 and see if that works. If it does not, then try anti-flicker mode. If neither of those work, and there will be some lights for which neither will work, realize that is a limitation of the camera. This issue...Show more →

A7CII and A7CR have variable shutter setting available too. The original A7C doesn't have it though.

Sep 05, 2024 at 02:04 AM

chiron
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p.2 #3 · p.2 #3 · Does mechanical shutter on A7CR or A7CII eliminate LED banding?

dclark wrote:
@tschopp@, Yes, I did look at the article referenced. Unfortunately is it pretty thin on information so it is speculation what may be the cause of the observations.

In response to the question does switching to mechanical shutter eliminate banding I think the answer is no, but it may well be that the banding will drop so low that it's not noticeable. I will try to explain my answer. First let me note that the Sony reference provided by Steve Spencer has some excellent graphics that help to understand this issue. You need to expand the explanations to see them. I have copied them below.

The first graph shows an example of pulsed light and the shutter curtains traverse the sensor height in the time of 3 pulses. If the light pulses are 1/120 sec, that means the shutter scan time is 1/40 sec, which is typical of a slow electronic shutter, but some cameras are much slower. The large the angle the slower the shutter curtain speed (electronic or mechanical). The width of the band is proportional to the shutter speed. The narrower the band the faster the shutter speed. Again if we assume the light pulse rate is 120/sec, the shutter speed looks like it is ~1/240 sec. So as the shutter slit traverses the sensor it goes in and out of sync with the light pulses and banding occurs. The slower the shutter curtain speed, the more bands are seen. If the shutter curtain speed were to increase so the scan time drops from ~1/40 to ~1/400 sec, it would be very nearly vertical and the change in illumination would be very little. In this case it would start out dark and, although it would brighten a bit, it will stay very dark. The change from ~1/40 sec to ~1/400 sec would be what might occur moving from electronic shutter to mechanical shutter. So in this case the answer to the question you pose is a qualified yes. Banding would not be seen but the unfortunate timing is such that very little light is gathered. The next frame might be better, depending on the random alignment of the open shutter with the light pulses. If the camera has the capability to detect the pulses and center the light pulses in the open shutter, the illumination would be high and there may be a slight non uniformity at the top and bottom of the image. If the camera has a fast electronic shutter, the benefit of switching to mechanical shutter may be very limited. A global shutter would be the limiting case of a vertical band.

Looking at the flash sync speed for the A7CR and the A7CII I see it is only 1/160 sec, which in not that fast. I don't see any data on the electronic shutter, but snapsy's data on the A7C is 1/16 sec. That is a 10X factor which means the banding should be considerably less, but the since the sync speed is about 2X slower than other cameras the residual banding (non-uniformity) will be more noticeable.

The second chart shows the case were the shutter speed is adjusted to be an integral number of pulses, in this case 1. In that case it does not matter how slow the shutter curtains are or how well it is synchronized with the pulses, it always gets one pulse of illumination. A slow shutter curtain speed does not result in banding. So if the camera has the capability to carefully adjust the shutter speed to equal an integer number of pulses the slope (i.e. the shutter curtain speed) does not matter. But the flatter the slope the more precisely the shutter speed needs to be set.

...Show more →

Given your explanation, why (or under what circumstances) would EFCS produce a result any different from full mechanical?

Sep 05, 2024 at 08:36 AM

dclark
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p.2 #4 · p.2 #4 · Does mechanical shutter on A7CR or A7CII eliminate LED banding?

chiron wrote:
Given your explanation, why (or under what circumstances) would EFCS produce a result any different from full mechanical?

Yes, I find that a bit of a puzzle. I notice in the referenced Sony discussion they state that turning off EFCS may help but they offer no explanation, and that is lumped together with switching to full mechanical shutter. It may be that some Sony cameras have an EFCS that is slower than the the mechanical shutter, although usually the EFCS is very fast. It is the electronic second curtain that slows down the full electronic shutter. The EFCS is on the sensor and the mechanical is above the sensor which has some impact on the shape of the sensor illumination, but I find that unconvincing as an important effect on banding. Maybe someone else has a good explanation.

Sep 05, 2024 at 08:55 AM

chiron
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p.2 #5 · p.2 #5 · Does mechanical shutter on A7CR or A7CII eliminate LED banding?

dclark wrote:
Yes, I find that a bit of a puzzle. I notice in the referenced Sony discussion they state that turning off EFCS may help but they offer no explanation, and that is lumped together with switching to full mechanical shutter. It may be that some Sony cameras have an EFCS that is slower than the the mechanical shutter, although usually the EFCS is very fast. It is the electronic second curtain that slows down the full electronic shutter. The EFCS is on the sensor and the mechanical is above the sensor which has some impact on the shape of the...Show more →

Might the EFCS turn on the sensor rows in sequence (albeit at a higher speed than data can be sequentially read from the sensor rows) producing a potential cycling mismatch with light pulses as the sensor is turned on? If this sequential turning-on of sensor rows took place at a faster rate than data can be read-out from the sensor rows, then the effect on banding would be intermediate at some point between a full electronic shutter and a full mechanical shutter. If so, then the difference between an EFCS and a mechanical shutter with respect to light-pulse banding would be that EFCS activates the sensor rows with a time-gradient while a mechanical shutter activates the sensor rows without a time-gradient (all at the same moment).

Sep 05, 2024 at 09:24 AM

snapsy
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p.2 #6 · p.2 #6 · Does mechanical shutter on A7CR or A7CII eliminate LED banding?

Just seeing this thread now. A mechanical shutter does not eliminate banding from LED lights, but since most mechanical shutters are faster than most electronic shutters there will be some situations where LED cycling frequency is low enough to not cause banding on a mechanical shutter but will on an electronic. Also, LED banding on mechanical shutters is more diffuse and thus less objectionable due to traveling physical edge of the shutter curtains.

An EFCS should behave the same as a fully mechanical shutter with respect to the situations where banding will manifest, although the presentation of the banding may be different since the leading edge of the exposure for each row is an electronic reset instead of the mechanical first curtain shutter.

Here's a comparison of how a ~2Khz light looks on a mechanical vs slow electronic shutter (Nikon Z6):

Sep 05, 2024 at 10:53 AM

goo0h
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p.2 #7 · p.2 #7 · Does mechanical shutter on A7CR or A7CII eliminate LED banding?

chiron wrote:
Less distracting and attention-getting.

I’m similar. Especially when casually following an event among a small group of people, mainly family. I hate the sound of the shutter banging away. In fact a last year (?) I bought a used a9II largely for that reason, and it’s become my main camera. I also really like the no blackout when taking photos. It’s something I really liked about rangefinder cameras.

Sep 05, 2024 at 11:30 AM

chiron
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p.2 #8 · p.2 #8 · Does mechanical shutter on A7CR or A7CII eliminate LED banding?

snapsy wrote:
Just seeing this thread now. A mechanical shutter does not eliminate banding from LED lights, but since most mechanical shutters are faster than most electronic shutters there will be some situations where LED cycling frequency is low enough to not cause banding on a mechanical shutter but will on an electronic. Also, LED banding on mechanical shutters is more diffuse and thus less objectionable due to traveling physical edge of the shutter curtains.

An EFCS should behave the same as a fully mechanical shutter with respect to the situations where banding will manifest, although the presentation of the banding may be...Show more →

Thank you for the explanation. Can you add to this to describe how the A9xx, the A1, and the A93 interact with flickering lighting and why they usually do not show banding? What are the limiting cases for these cameras, where they will begin to show banding?

And what will happen if the A1 II is still not a global shutter but increases its sensor readout speed to be significantly faster than the A1's (while retaining high mpix, one would hope and expect)?

Sep 05, 2024 at 11:36 AM

snapsy
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p.2 #9 · p.2 #9 · Does mechanical shutter on A7CR or A7CII eliminate LED banding?

chiron wrote:
Thank you for the explanation. Can you add to this to describe how the A9xx, the A1, and the A93 interact with flickering lighting and why they usually do not show banding? What are the limiting cases for these cameras, where they will begin to show banding?

And what will happen if the A1 II is still not a global shutter but increases its sensor readout speed to be significantly faster than the A1's (while retaining high mpix, one would hope and expect)?

All electronic shutters are the same with respect to banding - it's the intersection of the sensor readout speed vs cycling frequency that determines how many bands there will be. I describe this fully with examples in my Rolling Shutter github project readme:

https://github.com/horshack-dpreview/RollingShutter

Sep 05, 2024 at 11:42 AM

snapsy
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p.2 #10 · p.2 #10 · Does mechanical shutter on A7CR or A7CII eliminate LED banding?

I just did a quick comparison of electronic vs mechanical vs EFCS for my 1920 Hz LED PWM light:

** removed **

As expected, EFCS has same # bands as mechanical but with a different presentation for the bands.

Sep 05, 2024 at 11:43 AM

snapsy
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p.2 #11 · p.2 #11 · Does mechanical shutter on A7CR or A7CII eliminate LED banding?

snapsy wrote:
I just did a quick comparison of electronic vs mechanical vs EFCS for my 1920 Hz LED PWM light:

** removed **

As expected, EFCS has same # bands as mechanical but with a different presentation for the bands.

Reposting the image composite - I was in a rush and forgot the Z's drop the shutter speed down to 1/2000 for EFCS. That was why the EFCS exposure looked so different from the fully mechanical shutter. Here is the corrected composite, all shot at 1/2000:

Image Composite: Nikon Z6, Electronic vs Mechanical vs EFCS on 1920 Hz LED PWM Light Source

Here's what that same light source like when captured with a global shutter:

Nikon D40 with 1920 Hz LED PWM Light Source

Sep 05, 2024 at 01:48 PM

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