Flash

[Damien Symonds]

Hi Kim, when I'm looking at the Flash data in exif in Bridge, some say "Did not fire", while others say "Did not fire, compulsory mode".

This seems to be across various cameras.

What does "compulsory mode" mean in terms of flash?

[Kim Howells]

Hi Damo.  Generally, the flash settings are auto, on, or off.  Compulsory means that there is a camera setting to say that the flash must fire. 

"Did not fire" on its own means that the flash wasn't set to compulsory, and did not fire.  So it may have been on auto and wasn't required, or it may have been set to "off".

"Did not fire, compulsory mode" usually means that the flash did not fire, when it was set to fire.  This can happen for a few reasons.  The camera may not have an onboard (pop-up) flash, and an external flash wasn't attached (physically or remotely), so the flash could not fire even though the camera setting was compulsory.  This can also happen if the flash is set to fire, but when half depressing the shutter, the on-board flash popped up and was pushed down by the photographer.  The other time it may not fire, is if the external flash had not recycled in time to fire, or misfired for some other reason.

However, there seems to be something else at play. I just looked at a series of images.  The first was taken with exif "fired, compulsory mode".  Seven seconds later, the exif was "did not fire".  Five seconds later, it was "did not fire, compulsory mode".  There was no change in settings at that time in-camera with respect to the flash (Speedlite attached via hotshoe).  I can't explain why only one of the "did not fire" had compulsory, as the flash should have been set to fire regardless of my settings and the light (it was not in an "auto" mode, it was manually set, and the mode wasn't changed between those photos).  I will have a look through some more images and see what I can find.  I do know at that point that the light had changed rapidly and I had potentially made some changes while shooting, but I wouldn't have thought I would have done that in the few seconds between these particular shots.

[Kim Howells]

I have learned you can't trust the exif, as it depends how the flash is talking to the camera.

The images I have taken using a wireless trigger for the flash, say "did not fire, compulsory mode" when the flash fired.

When the Speedlite was mounted to the camera hotshoe, and the flash didn't fire (almost certainly because it hadn't recycled and didn't have enough power to flash), the exif still said "fired, compulsory mode".

So while the exit demonstrates the intent, it doesn't necessarily show what actually occurred!

[Damien Symonds]

Thank you.

So can you take a look at this thread?  Do you agree that it really truly looks like flash?  The exif must be lying, surely?

[Kim Howells]

It does look really "flashy", but I am not 100% sure.  I keep changing my mind every time I look at it, but at first glance I would have said flash was used.  Then I wonder if the light in front of the rear leg of the frog looks like it's more from above (the sun) than from a flash, so it could also be really harsh, bright midday/early afternoon sunlight. 

The settings may give us a few clues.  She shot in a semi-auto mode (shutter priority), and her aperture is as small as it can go on that lens, which definitely indicates that the ambient light was very bright if she was forcing it to have that shutter speed.  In this mode, she would have to choose to fire her flash and make it pop up (or not) - it wouldn't do so automatically.