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Canon T1i: EFSC has large variation in shutter delay
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rjlittlefield
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PostPosted: Sun Jun 26, 2011 12:59 pm    Post subject: Canon T1i: EFSC has large variation in shutter delay Reply with quote

Summary: my Canon T1i has over 500 ms variation in shutter delay when running in Live View mode with EFSC (electronic first shutter curtain).

More details...

For a variety of reasons, I recently got interested in using a combination of Live View / EFSC and flash exposure with my Canon T1i camera. As far as I know, Canon does not support this combination. Connecting a flash to the camera disables EFSC and the camera reverts to mechanical first curtain. This behavior seems odd, since the camera also supports second curtain flash sync, but that's the way it is.

Anyway, it finally occurred to me that I could get around this limitation by just not connecting the flash to the camera, thus letting the camera run in EFSC mode, and triggering the flash by some separate mechanism. This seemed pretty straightforward, so I built the following little piece of electronics:



I noticed in breadboard that there seemed to be some variation in the timing, just listening to the sound sequence of "zing, pop, click" corresponding to start of exposure, flash going off, and shutter closing. But I figured a bit of variation was to be expected, so I just made the delay adjustable and figured I'd tune it after I got everything boxed up.

After I got the flash delay timer boxed up and started using it, I noticed that every once in a while the flash would trigger prematurely, so that actually the whole exposure occurred after the flash was gone. Black frame, not nice. Clearly a glitch in the electronics -- or so I thought.

At that point I was getting hungry for solid data, so I decided to set up some instrumentation. I hooked up an oscilloscope watching the flash trigger line, synced by the shutter trigger line, and pointed the camera at the oscilloscope so I could see when the picture was being taken.

When I first turned everything on, the timings looked great -- shutter delay about 170 milliseconds, almost perfectly repeatable, flash trigger right on schedule as set. No trouble at all dialing the flash trigger right into the middle of a 1/15 second exposure.

But then I realized I had the camera set to normal mode, not Live View.

So I switched it over into Live View. That changed the picture a lot!

It turns out that my electronics are working as designed.

The problem is that in Live View, the camera has a large variation in shutter delay between receiving a trigger and actually taking a picture. In one series of 100 frames, "large variation" meant that the shutter delay varied from a low of 70 milliseconds to a high of just over 500 milliseconds. Here are some examples at 100 ms/div:



The bottom line is that using this approach, I cannot use less than about 0.6 seconds flash delay and 0.6 second exposure time. Using a shorter flash delay or a shorter exposure time means that every once in a while either the camera will finish before the flash fires, or the flash will fire before the camera starts.

I think this will still be useful on occasion, but it doesn't work nearly as nicely as I had hoped.

I tried a variety of image sizes and formats, with the camera connected and not connected to a computer. No obvious difference in behavior. The key issue seemed to be only whether the camera was set to run in Live View or not.

--Rik
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seta666



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PostPosted: Sun Jun 26, 2011 1:36 pm    Post subject: Reply with quote

I do not understand why you are getting this delay; as far as I know my EOS 5D mkII (T1i should be the same) can fire a flash while in silent mode 1. It has to be a canon flash (compatible may be enough, eg Metz) and be shoth in manual mode (no E-TTL support)

http://speedliting.com/forum/showthread.php/312-Canon-5DMKII-Manual-270EX-Flash-Works-in-Live-View-Silent-Mode-1!

That flash is the one I own, I also have a couple of yongnuo flashes than can be slaved from the 270EX but I do all my shots with continuous light source

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RogelioMoreno



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PostPosted: Sun Jun 26, 2011 2:22 pm    Post subject: Reply with quote

Javier,

It is good to know the EOS 5D mkII allows you to fire the flash while in live view, my 50D does not has the option to set the flash to manual mode. I would like to know if the current Canon models allow that.

Rogelio
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seta666



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PostPosted: Sun Jun 26, 2011 2:33 pm    Post subject: Reply with quote

RogelioMoreno wrote:
Javier,

It is good to know the EOS 5D mkII allows you to fire the flash while in live view, my 50D does not has the option to set the flash to manual mode.

I guess the on camera flash can not be set to manual mode, but any external flash should. The 270EX has no buttons whatsoever, is fully controled from the camera. Any digic 4 camera can control external flash power from the camera menu, even the cheap EOS 1000D ( I have a cheap yongnuo E-TTL flash and can be controlled too, YN-468)

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rjlittlefield
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PostPosted: Sun Jun 26, 2011 2:51 pm    Post subject: Reply with quote

I am delighted to hear that the 5D MKII works the way I would like. But in my tests the T1i is different.

Here are settings I just now re-tested. This state was reached by pressing the DISP button to "Clear Speedlite settings", followed by setting manual flash at 1/128 and 2nd curtain.



I tested this with a 5 second exposure started in Live View by pressing the shutter button. The desired behavior is a quiet "zing" followed by 5 seconds of silence, followed by the flash going off just before shutter closing and mirror cycling. But the actual behavior is that the mirror drops and re-opens, then there is 5 seconds of silence, followed by the flash etc. I tried it with an MP-E 65 mounted, and also while looking into the front with only a chipped adapter in place. The sequence definitely starts with mirror cycle.

Do you see anything that I have missed?

--Rik
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Pau
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PostPosted: Sun Jun 26, 2011 3:14 pm    Post subject: Reply with quote

7D don't allows flash in live view Silent mode (EFSC), it don't send flash tiggering signal, and this is clearly stated in the manual. I'm very surprised by the Javier affirmation that 5D mkII allows it.
With the 7D and some other Canons if you connect a Canon EX flash it fires because the camera automatically disables Silent Mode switching to normal LV mode (and the mirror drops for mettering if the flash is set to auto). With a not dedicated flash the camera stays in silent mode and the flash don't fire.
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seta666



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PostPosted: Sun Jun 26, 2011 3:29 pm    Post subject: Reply with quote

rjlittlefield wrote:

Do you see anything that I have missed?


As far as I remeber the EOS 1000D I owned worked as it should in silent mode with canon flash, but mirror flipping after shots was quite anoying (one of the reasons I sold it too)
From your picture flash/camera settings seem OK, now I remember the rebel's have no silent mode settings, should be on all the time
Here I someone with same problem as you, seems to be T1i behaviour

http://photo.net/canon-eos-digital-camera-forum/00TNxM

EOS 40D or 50D should work better in this regard

information regarding 5d mkII here
http://photonotes.org/forum/viewtopic.php?t=996&sid=446757bfa99772ab62c0550249074752

However, I just conected my 270EX to the camera and it seems to disable slilent mode when using the flash, so shutter closes at the beggining of the exposure; no mirror flipping though

So the information I gave (and took from the link above was wrong)
If liveview is set to silent mode and you conect a canon flash it automatically switches to disabled setting
If you conect a non canon flash you have to disable silent mode manually, otherwise flash will not fire

Sorry for the missinformation, I was wrong (Pau was right)
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elf



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PostPosted: Sun Jun 26, 2011 4:08 pm    Post subject: Reply with quote

Have you tried a longer timeout between images to ensure the camera CPU isn't doing any housekeeping?
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DQE



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PostPosted: Sun Jun 26, 2011 4:32 pm    Post subject: Reply with quote

A helpful book is "Mastering Canon EOS Flash Photography" by David Hobby. Its available for $9.99 as a Kindle ebook from amazon.com. For the price, it's hard to beat. <EDIT: I moved this paragraph to the top of the post>

This info may help, linked below. It is supplementary material for a new book on Canon flash photography. I have the full e-book via Kindle and have found it to be useful information, worth the purchase price for the ebook. I believe it is also available in print form.

http://rockynook.com/book/122/mastering-canon-eos-flash-photography.html

See the downloadable PDF files, especially the Appendix C - Features Table. In this table there are entries for using Live View with flash. On page 4 it provides info about LIve View and flash in the right-most columns for a zillion camera bodies. In the next paragraph I provide the definitions of these column/table entries.

From the full book text, the above table column name "Live View silent mode" means the camera can use electronic first curtain in Live View for quieter performance. Silent mode is not compatible with flash". The column title "LV, no ext flash" means that "the camera cannot fire studio flash units (ie non-Speedlite sync-only flash units) when in Live View mode."

There is also a TOC and a useful Appendix E chart on grouping multiple Speedlites at the above linked web page.

http://www.amazon.com/Mastering-Canon-Flash-Photography-ebook/dp/B004J4VVN8/ref=sr_1_1?ie=UTF8&m=AG56TWVU5XWC2&s=digital-text&qid=1309130059&sr=1-1

It covers all SLR cameras back to what seems like the beginning of time, matrixed against all Canon and many non-Canon flash units, up to the newest models AFAIK. I highly recommend this book for people who want a reasonably comprehensive and detailed reference to how Canon flash units work in combination with various cameras. It has a short section on macro flash, covering the Canon ring and twin flash units basic.
----------------
I also acquired the new (2011) book, "Speedliter's Handbook" by Syl Arena, and am enjoying its extensive information and detailed instructional material. As with the other book, there is some material here that is not available in the Canon manuals.

EDIT: The Strobist also recommends this book, briefly reviewed on his bookshelf page here:

http://strobist.blogspot.com/2006/04/strobist-bookshelf.html

I personally believe that these two books complement each other, with information and its organization differing enough to make it worthwhile to own both, especially considering the relatively low price of the first book

This book has some text about live view and flash. Not sure it is relevant, but may be indirectly relevant:

"Also, any time that you shoot stills in Live View (from your camera's LCD), the camera switches to Evaluative metering regardless of the mode you have selected"

---------
While I'm commenting on lighting books, my personal fav lighting book is: "Light: Science and Magic: An Introduction to Photographic Lighting". One can "look inside" at amazon and see some content in the usual fashion.

Hope this helps.

The information Rik presents and the comments are interesting. I gather that there are differences between the 5DII camera body (which I also own) and the others.
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Charles Krebs



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PostPosted: Mon Jun 27, 2011 11:23 am    Post subject: Reply with quote

I am nearly certain that the 5DII is no different in this regard (ability to flash sync in silent mode). Pretty sure what was said here still applies to all Canon bodies:
http://www.photomacrography.net/forum/viewtopic.php?t=8943
Quote:

If a Canon dedicated flash is used, the camera senses it, and will automatically revert to the “normal” mode. In this case if E-TTL flash metering is used the mirror will cycle to pick up the metering pre-flash. If the flash is set to manual then there is no metering pre-flash and the mirror will not cycle.


When a Canon body that is in live view, silent mode (default in digital Rebels, user set in xxD and higher bodies) has a flash attached two things can occur....
1) If it is a non-Canon, "non-dedicated" flash there will be no sync signal and the flash will not fire.

2) If it is a Canon flash, or a properly "dedicated" flash the camera body can sense that a flash is attached. It then automatically reverts to the "non-silent" mode. The first (mechanical) shutter curtain will first close, and then an exposure will begin in normal fashion. During the exposure a flash sync signal is sent. Since it happens very quickly and automatically most people do not realize the change in "procedure". (On the bodies that use separate motors for mirror and shutter, there will be no mirror action if the flash is set to a manual power setting. For E-TTL the mirror must cycle to catch the metering pre-flash. On the digital Rebels I would need to check to see if the mirror does indeed cycle before the exposure begins when the flash is set to a manual power. Based on what Rik has said above it does with his T1i. I can check later today with a T3i. But since the mechanical first curtain needs to close, and on these bodies a single motor drives both mirror and shutter it is not unexpected).

Rik's results are interesting. I do not know what is involved to "clear" the sensor electronically, and then have the EFSC feature. My understanding, based on comments from people far more knowledgeable than myself is that it is apparently is a pretty good "feat" with a CMOS sensor. My (wild) guess is that there are significant timing functions going on in the camera, with live view read-out and such. Then for EFSC the timing needs to be established so that the electronic first curtain will be in perfect synchronization with the mechanical second shutter curtain. Perhaps the variable delay is caused by the location the camera happens to be in within a timing cycle when the shutter actuation is sent. You would have to think that there must be a very good reason (perhaps this varying delay) why Canon did not provide a flash sync signal from this mode. Much better to slip automatically into using the first shutter curtain than to tell people they need to use a 1/2 second shutter speed with flash! Probably only obsessive types like us here that even notice the operational change! Wink
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rjlittlefield
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PostPosted: Mon Jun 27, 2011 12:49 pm    Post subject: Reply with quote

I was interested to notice that the variable and occasionally long delay doesn't have anything to do with flash. After all, in my setup the camera has no clue that there's a flash involved.

In essence, the message for my T1i is that "If I care about timing, stay away from Live View." In normal mode, I get a very consistent 170 ms delay. But turn on Live View, and the delay starts bouncing all over the place.

Why that is, I can only speculate. That said, I suspect it's an incidental feature of how the firmware is organized. To get a consistent delay would require interrupting operations in progress. Usually the hardware can do that OK, but it's a lot harder writing software to handle interrupts gracefully than it is to just check at convenient times. I would not be surprised if the firmware is organized as a few large non-interruptable chunks wrapped in a do-forever event loop.

The behavior is a little unfortunate for this application. But on the other hand, if it also makes the firmware more reliable because of permitting a simpler design, then in the grand scheme of things it's probably a good tradeoff.

--Rik
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ChrisR
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PostPosted: Mon Jun 27, 2011 3:53 pm    Post subject: Reply with quote

Do I remember correctly that there's some sort of light on the back of the camera when the shutter opens?
There is the often-reported little noise.

Perhaps it would be relatively simple to fire the flash in relation to one of those triggers?
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rjlittlefield
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PostPosted: Mon Jun 27, 2011 4:10 pm    Post subject: Reply with quote

ChrisR wrote:
Do I remember correctly that there's some sort of light on the back of the camera when the shutter opens?
There is the often-reported little noise.

Perhaps it would be relatively simple to fire the flash in relation to one of those triggers?

I see no light on this camera, not until the exposure is finished and the image is being written to SD card (if one is installed). [Warning: this observation is incorrect -- see discussion HERE and following.]

The noise seems like a good bet, except that it would be the devil's own time to use by itself since it's pretty quiet and non-distinctive compared to other routine sounds coming from the camera and attached mechanics. Probably I could arm an audio detector based on the electrical trigger, but I'm a bit short of time for mucking around with that complexity right now.

--Rik

Edit: to add correction about the "no light" observation.


Last edited by rjlittlefield on Mon Dec 09, 2013 10:43 am; edited 1 time in total
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Craig Gerard



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PostPosted: Mon Jun 27, 2011 5:13 pm    Post subject: Reply with quote

Pau,

I don't have a 7D (yet), but I am curious to know if the built-in wireless speedlight transmitter is able to provide a workaround approach? I am not familiar with that particular feature of the 7D. How is it initiated?

*Later Note: Pau, I read your earlier post, more carefully this time, my question has been answered.

However, given the details of the flash/Live View/Silent Shoot process and Rik's timing observations, Canon have good reason to turn Silent Mode off when using flash.


Craig

*edit: added *Later Note:
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rjlittlefield
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PostPosted: Mon Jun 27, 2011 6:36 pm    Post subject: Reply with quote

Craig Gerard wrote:
However, given the details of the flash/Live View/Silent Shoot process and Rik's timing observations, Canon have good reason to turn Silent Mode off when using flash.

No doubt they have good reasons, but I don't think my observations reveal what they are.

Consider the following.

The camera is able to operate in normal mode with second-curtain sync. In this mode, the sequence is:
- raise mirror
- open shutter
- wait during most of exposure
- trigger flash
- wait a little more
- close shutter.

If the camera were able to operate in Live View mode with second-curtain sync, then the sequence would be
- raise mirror
- open shutter
- Live View
- clear sensor
- initiate EFSC

- wait during most of exposure
- trigger flash
- wait a little more
- close shutter.

Notice that from the standpoint of the mirror, shutter, and flash triggering, there is no difference in these sequences. The differences are only in electronic signals to the sensor to implement Live View and EFSC.

It is easy for me to imagine good reasons for the variable delay. As discussed earlier, this probably simplifies the firmware a lot.

But so far I have not been able to imagine any hardware reason why Live View should interact with flash triggering.

--Rik
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