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I want to build a sensor for my Canon EOS 5D III that automatically takes a picture whenever a lightning strikes. I know that you can as well simply keep the shutter open and set the aperture etc accordingly, but I want to try this approach as it feels more "healthy" for the camera.

The sensor is definitely very fast and will trigger a shot almost instantly, but I wonder what delay the camera itself brings into the game? To be clear: I'm not talking about the shutter speed (e.g. 1/200 sec) but the delay, thus the amount of time between triggering a shot (via shutter button or remote control) and the camera actually starting to record the image.

I could not find any info on that. The delay will surely be quite small, but I'd like to be sure that it is small enough before I start building my sensor.

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  • \$\begingroup\$ There are commercially available lightning triggers that work quite well with cameras much slower than the Canon EOS 5D Mark III. So the proof of concept has already been demonstrated many times over. If you build a trigger properly it will allow you to automate capturing lightning. It's already been done countless times. \$\endgroup\$
    – Michael C
    Jul 21, 2017 at 10:56

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Shutter delay, more commonly known as 'Shutter Lag' is approx 0.14s on the EOS 5D Mark III, Canon claims that dependent on camera settings the lag time can be reduced to around 59ms

Full article here: http://cpn.canon-europe.com/content/education/technical/inside_canon_eos_5d_mark_iii.do

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I think it's called shutter lag. If you search for that you should get several results. I found this: http://www.imaging-resource.com/PRODS/canon-5d-mkiii/canon-5d-mkiiiA6.HTM

...which states the response time anything up to 0.144 seconds. Remember that focus settings and mode settings will have an impact, especially focus: if it's set to manual focus, it doesn't need to enable and process the focusing measures etc etc, so that would speed it up significantly. Look for the table headed Shutter Response (Lag Time)

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  • \$\begingroup\$ Thanks for the clarification and the link! I think I was looking for the wrong term here (not a native English speaker). The number is surprisingly high, but I will give it a try nevertheless. I will definitely use manual focus (using a 14mm for that purpose) and mirror lockup, so maybe this brings the number down a bit. \$\endgroup\$
    – Rob
    Jul 18, 2017 at 13:15
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    \$\begingroup\$ I reckon the less processing you can do the better as well...make sure you disable: in-camera noise reduction, autofocus, bracketing, silent shooting, liveview. I'm sure it's been done plenty of times, there are plenty of products on the market that do the job: search for Lightning Activated Shutter Triggers \$\endgroup\$
    – laurencemadill
    Jul 18, 2017 at 13:20
  • \$\begingroup\$ @Robert I just realised my avatar photo is lightning too...I seem to remember it was a 13 second exposure and a lot of luck \$\endgroup\$
    – laurencemadill
    Jul 18, 2017 at 13:21
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    \$\begingroup\$ You're right, there are a lot of gadgets for that, but as I am a developer myself, this is a matter of professional honor ;-) And yes, you still need a lot of luck, of course. \$\endgroup\$
    – Rob
    Jul 18, 2017 at 13:25
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    \$\begingroup\$ @EricShain yes for the first strike, but frequently the same path is followed again several times, so when you're looking at it, it can appear to last much longer. Also, a single strike can last much longer, a single strike of over 7 seconds in France: independent.co.uk/news/science/… How I wish I could have seen that haha \$\endgroup\$
    – laurencemadill
    Jul 19, 2017 at 8:36
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It is highly variable depending on the settings active in the camera at the time it is triggered. The 59ms published by Canon is the minimum rated time used when everything that can lengthen the lag time is turned off. This includes (roughly in order of amount of influence):

  • Autofocus
  • Automatic metering
  • Aperture settings other than the lens' maximum aperture

Additionally, if more than one frame is desired, to minimize the delay between frames, also turn off:

  • High ISO Noise reduction
  • Long Exposure Noise Reduction
  • Peripheral Illumination correction
  • Auto White Balance
  • Auto Lighting Optimizer
  • Chromatic Aberration correction
  • Distortion Correction
  • Resize to M1, M2, or S
  • Multiple Exposures
  • HDR presets
  • White Balance Bracketing
  • Exposure Bracketing

Even with everything turned off, the maximum frame rate will be 6.0 fps, or 167ms between frames.

Additionally, you want to insure metering is already active such as is the case with a half shutter press (even though you're not using automatic metering - because the same state that includes active metering also has the camera preset to fire on the full press). One setting that can help make this easier is to set the metering time out to the longest available setting so that a half-press of the shutter button (or the AF-ON button or the AE-L button) will keep the camera in the 'active ready state' for longer before needing to be refreshed.

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