Quirks of Canon R7 full electronic shutter

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Quirks of Canon R7 full electronic shutter

Post by rjlittlefield »

SUMMARY

Using full electronic shutter, my Canon R7 camera shows up to 130 milliseconds variation in lag time between cabled remote shutter pulse and start of exposure. The pattern of this delay varies strongly depending on circumstances. In some situations the delay varies almost uniformly across the whole range; in other situations the delay usually falls in a narrow subrange but occasionally is much larger or smaller. The range of variation affects the settings that can be used safely for "mid curtain sync" using externally synchronized flashes. Exposure time of 1/4 second, with flash triggered 1/4 second after the shutter pulse, would be reliable in all the tests I ran.

My experiments confirm that the full electronic shutter travel time is about 30 milliseconds, moving from top of image to bottom of image with a constant speed so that a moving vertical line is captured as a slanted straight line. Interestingly, the mechanical and electronic 1st curtain shutters move in the opposite direction, from bottom of image to top of image, and the speed is not constant so that a moving vertical line is captured as a slanted curved line.

With the Canon R7, unlike earlier models, a flash trigger signal is generated when using electronic 1st curtain shutter (versus full electronic shutter). Thus there is no need for external flash synchronization unless full electronic shutter is used.

DETAILS

I recently purchased a Canon R7 camera to use as my main camera for focus stacking. One of its nice features is a full electronic shutter "silent mode" that is totally free of mechanical vibration and shutter wear.

Like many other cameras that use full electronic shutter, the R7 does not provide a trigger signal for electronic flash.

The standard way to address this lack is to use "mid curtain sync", in which the flash is triggered by an externally generated pulse that is somehow synchronized with the start of exposure. Common practice is to use a delay time that is fixed with respect to the shutter pulse that triggers the exposure, with no input from the camera itself.

Ideally the camera would have perfectly constant delay from trigger pulse to actual exposure. In that case the minimum required exposure time would be only a little more than the time needed for sensor readout, with the flash sync pulse scheduled to occur essentially one readout time after the start of exposure, just after the first shutter has progressively cleared the whole sensor and before readout has begun.

However, previous experience with a Canon T1i in EFSC mode made me suspicious that the R7 might have significant variation in shutter lag time.

So, I hauled out some equipment and tested it.

Indeed, the R7 does have significant variation in shutter lag time.

Further, the pattern of variation depends on circumstances in mysterious and intriguing ways. In some situations the delay varies almost uniformly over a range from roughly 70 to 200 milliseconds at center of image. In other situations the delay usually falls in a narrow subset of that range, but occasionally and unpredictably hits the extremes.

The major results are summarized in this illustration:

Image



The instrumentation used here is essentially the same setup that I used in earlier tests.

It consists of an old-fashioned analog oscilloscope set up to sweep at 50 ms/div when triggered by the start of exposure pulse that is provided to the camera. The camera photographs the oscilloscope screen. While the exposure is happening, the camera records the current position of the scope’s bright dot, along with a dim history of the dot’s previous positions that is made visible by long-lived weak glow of the scope’s phosphors.

The timing of the start/end of exposure is indicated by the horizontal limits of the bright line.

For added context, the vertical axis of the scope trace is set up to show the flash trigger signal that is produced by an external synchronizer. The timing of the flash trigger is controlled by a setting on the synchronizer, and the overall goal is to find some combination of flash trigger timing and exposure duration that reliably places the flash trigger somewhere inside the exposure interval.

As shown in the pair of images above, exposure at the location of the bright line can start anywhere from about 70 to 200 ms following the exposure pulse.

To be more sure that I actually had found the limits, I shot 1000 exposures and ran them through a program to analyze the images. In addition to providing the max/min delays, that program also provided a mass of data that allows to look at the distribution of delays.

Here is the first set of data that I got:

Image


For the most part, this graph showed what I expected to see: a random distribution of delays that uniformly filled the entire interval of 70-200 ms.

I was surprised to see the obvious patterning for the first 300 exposures. That clearly means something, but I have no idea what.

Nonetheless, the uniformity of the distribution is compelling. Here is the same data, sorted by increasing delay time. Aside from a few minor jiggles, I see a nice straight line that indicates a uniform distribution.

Image


This run is with the camera USB-tethered to a Mac mini M1 computer, transferring small coarse JPEG files to minimize transfer time and file space. I repeated the exercise with different file formats and did not trip over any changes in behavior that seemed very interesting.

However, the delay time between exposures turned out have a huge effect on the results. The Run #1 results shown above were with about 1.4 seconds between exposures. When I increased that delay to be 5 seconds, the pattern got wildly different:

Image



Sorting that data by delay time produced this summary:

Image



I have no idea what causes this distribution to be so very far from uniform, and wildly different from the earlier runs.

I expect that investigating that aspect would be a fascinating diversion, but I’m pretty sure that I have better things to do with my time so I’m trying to stay disciplined and not start chasing that squirrel.

It is enough for me to know that 250 milliseconds exposure time, combined with 250 milliseconds flash delay, seems to reliably place the flash comfortably inside the exposure interval.

Of course, this test only measures the exposure delay at the center of the image. The delay at top and bottom of image will be different, depending on the direction and speed of how the shutter sweeps across the image.

To explore the direction and speed of shutter sweep, I changed the setup so that the dot on the oscilloscope was continuously moving quickly between the top and bottom of the frame, while simultaneously moving sideways across the frame. From the standpoint of the camera, the oscilloscope was displaying a thin vertical line that swept across the screen.

Photographing that line, with settings that are suitably shortened to show both the duration and relative timing of the shutter sweep, produced this picture:

Image



Note that this is 5 milliseconds per division. The start of exposure is seen to vary by just under 30 milliseconds from top to bottom, beginning at the top, and the edges of the bar are essentially straight implying constant vertical speed of the shutter.

Running the same experiment with full mechanical shutter and with electronic 1st curtain shutter gives quite a different picture:

Image


Image



In these cases, the shutter sweep is from bottom of image to top of image, and is significantly nonlinear. In retrospect, the nonlinearity makes perfect sense in terms of a mechanical curtain that has to accelerate from a standing start not far outside the frame. But I had not thought about that before running the experiment, and I was surprised to see the obvious curve in the results.

Back to the full electronic shutter, there is one other quirk that I have read about but have not explored. That quirk, apparently shared with many other cameras, is that in full electronic shutter mode, fewer significant bits are captured in the raw data. Raw data in other modes is reported to be 14 bits, but in full electronic mode this is reduced to 12 bits, probably to keep the readout time down to 30 milliseconds. There’s a discussion thread at https://www.dpreview.com/forums/thread/4662859 , that has comments and graphs by Bill Claff of PhotonsToPhotos.

It's not clear to me how much I will care about the reduction in bit depth. The difference should be easily detected as coarser gradation in very dark areas, but those are rare in the deep high magnification stacks where I would particularly care about using full electronic mode. Anyway this is a matter for future investigation and I’ll probably put it off until I have a suitable subject already mounted up because I care about it.

That’s enough for now. Of course I wrote this for my own purposes, but I hope that some of you find it interesting also.

--Rik

Adalbert
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Re: Quirks of Canon R7 full electronic shutter

Post by Adalbert »

Hi Rik,
Congratulations on your purchase of a new camera!
Yes, the full electronic shutter is really fun.
I trigger the flashes in ½ shutter speed + delay.
It runs really stable at shutter speed 1/10 s and of course larger.
BTW, the storage of data is problematic, so the break between two photos must be long.
Best, ADi

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Re: Quirks of Canon R7 full electronic shutter

Post by enricosavazzi »

I don't know if the following is relevant to the R7, but when timing the shutter delay of electronic shutter (or electronic first curtain) it is a good idea to check in the camera settings whether something called "light flickering reduction" or something like it is activated. This is a setting only available for EFC or electronic-shutter mode, that checks for flickering artificial illumination and delays the first curtain release by up to 10 ms to minimize the flickering. This setting usually also needs to be manually configured for 50 or 60 Hz mains frequency. The result is that the actual shutter delay is stochastically spread over a time span of roughly half the AC mains period.
--ES

rjlittlefield
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Re: Quirks of Canon R7 full electronic shutter

Post by rjlittlefield »

Adalbert wrote:
Sun Oct 02, 2022 2:18 am
I trigger the flashes in ½ shutter speed + delay.
It runs really stable at shutter speed 1/10 s and of course larger.
Is this for your Canon M6 Mark II ?

In any case your camera must have less variation than my R7.

With my R7, shutter speed of 1/10 second = 100 ms would cause a lot of the flashes to be missed because they occured too early or too late. The absolute minimum for mine would be a little over 160 ms: 30 ms to get both shutters open + 130 ms variation in start time.

If there were some way to synchronize against actual start of exposure then a shorter time could be used. On my earlier experiences with Canon T1i, it turned out that the camera did accidentally provide two hints that might have been used to improve the synchronization. One of them was the small "zing" sound that occurred at start of exposure in EFSC mode. The other was a light on the back of the camera, as described at http://www.photomacrography.net/forum/v ... 7969#87969 . I never investigated the sound, but the light could have been used to reduce variation to about 16 ms. It is possible that such hints exist with the R7 also, but they would take a lot of time to investigate and exploit so I probably won't do that.

BTW, the storage of data is problematic, so the break between two photos must be long.
True, but I think this was not an issue in any of the tests that I ran. The tethering program that I used (Canon EOS Utility 3) provides a transfer progress bar, and I took care to set the timing so that the bar had stopped before another picture was taken. In addition I ran long sequences, 1000 shots, and saw that all sequences ran at the intended speed and captured all the frames.

enricosavazzi wrote:
Sun Oct 02, 2022 5:40 am
I don't know if the following is relevant to the R7, but when timing the shutter delay of electronic shutter (or electronic first curtain) it is a good idea to check in the camera settings whether something called "light flickering reduction" or something like it is activated. This is a setting only available for EFC or electronic-shutter mode, that checks for flickering artificial illumination and delays the first curtain release by up to 10 ms to minimize the flickering. This setting usually also needs to be manually configured for 50 or 60 Hz mains frequency. The result is that the actual shutter delay is stochastically spread over a time span of roughly half the AC mains period.
The R7 does offer anti-flicker shooting. It works in all shutter modes and automatically detects 100 versus 120 Hz.

But in these tests, anti-flicker was turned off.

--Rik

blekenbleu
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Re: Quirks of Canon R7 full electronic shutter

Post by blekenbleu »

rjlittlefield wrote:
Sat Oct 01, 2022 9:34 pm
I was surprised to see the obvious patterning for the first 300 exposures. That clearly means something, but I have no idea what.
Canon's systems-on-chip DIGIC processors are proprietary, but execute ARM instructions.
ARM microcontrollers with which I am familiar have hardware support for timers, with integer clock dividers and counters,
often used for stepper motor and pulse width modulation control.
Those patterns for shorter delays may be artifacts of values set by ARM instructions, which then get randomized
by interrupt latencies when timers need to be reloaded to support values longer than a single hardware delay.
Metaphot, Optiphot 1, 66; AO 10, 120, and EPIStar 2571
https://blekenbleu.github.io/microscope

Adalbert
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Re: Quirks of Canon R7 full electronic shutter

Post by Adalbert »

Hello Rik,
Is this for your Canon M6 Mark II ?
yes.

I trigger the camera by cable and have to take into account
the delay between the release and the opening of the shutter.

Best, ADi

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Re: Quirks of Canon R7 full electronic shutter

Post by rjlittlefield »

rjlittlefield wrote:
Sun Oct 02, 2022 10:34 am
It is possible that such hints exist with the R7 also
Even better...

The R7 has an option to produce audible clicks at nominal start and end of exposure. (This is with electronic shutter, but "Silent shutter function" off.) I do not hear these clicks in the headphone output, but they are easily detected with an external microphone. Synchronizing on the start of the first click while displaying the microphone output produces this picture:

Image

I shot 500 repetitions. 498 of them were essentially duplicates of this same picture, right down to the minor peaks in the "click" waveform, with no significant variation in relative timing of the click and the exposure. The other 2 pictures looked very different at first glance, but on closer study I saw that the click and the exposure had the same relative timing in those also. The difference in the picture was only that the scope's sweep had started at the wrong time, perhaps a premature trigger due to room noise.

So, it seems that synchronizing flash from the audible click would be a very precise solution. According to the scope traces, using a 40 ms exposure duration (1/25 second) and triggering flash at 32 milliseconds after start of click would put the flash nicely in the middle of the 10 milliseconds when the whole sensor is exposed at the same time.

--Rik

TheLostVertex
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Re: Quirks of Canon R7 full electronic shutter

Post by TheLostVertex »

I have gone through this whole process with my m6 mkII before. As stated, 1/10sec manually syncing the flash is pretty stable. I found that I could decrease that to nearly 1/20 of a second by dramatically increasing the wait time between exposures and turning off various display options. I suspect writing to the card and image processing causes some amount of delay between the shutter signal being sent, and the actual process that needs to be called for that to actually happen. In anycase, the amount of delay between exposures to moderately decrease the variance wasnt worth it.

I have since switched to just using constant light for my m6II, though that has caused its own problems. Mainly the rolling shutter that sometimes causes issues with vibration. I also have an r5, but havent investigated flash syncing it since I use that on a portable rig with constant illumination as well.

The inbuilt focus stacking function is really a joy to use. If I can offer my experience for a very enjoyable shooting process with your new camera, the canon bluetooth remote, ef/rf100mm, and a video light make for a very enjoyable focus stacking process using the inbuilt focus bracketing function. I have also had good success using raynox diopters when I want to increase the magnification to around 2xish. If you decide to use the inbuilt focus stacking, I also highly recommend making a custom function that has auto focus removed from the shutter button(back button focusing) and continuous AF turned off, with full time MF turned on in the settings. It makes setting up to shoot a stack with in the lens's full range much easier. If there is any interest I could make a short video for my R5 set up.

-Steve

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