The above two shots were taken a minute apart on Saturday at Leeds Castle. The first uses purely ambient light and lacks drama - details in the sky have been lost and the subjects' faces are poorly lit. I therefore decided to liven things up with a bit of off-camera flash.
I asked the chauffeur of the Rolls Royce to hold a 580EX II Speedlite fitted with a Lastolite micro Apollo. This was set to slave mode and then triggered with an ST-E2 transmitter. The flash head was rotated so that the light could be directed at the couple and the wireless sensor at the transmitter.
Ambient light was underexposed by 2 stops and flash exposure compensation of -2/3 stop was used.
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David, I'm a bit confused with using ETTL flash with my camera in manual mode (5D2 and 580EXII). For portraits I'm killing the ambient with 160shutter and working at F5.6, but the ETTL is seriously underexposing my scene (mainly white). Is having to FEC+ normal? Just seems like the ETTL should be doing a much better job.
Hi Mark,
It is, I'm afraid - particularly when scenes are predominantly low- or high-key. It's the classic problem caused by determining any exposure using reflected light.
In the situation you're encountering, the white surfaces are reflecting back a lot of flash light and the camera is consequently under-exposing the shot. Bear in mind that the camera doesn't know what it's looking at - it can't tell that the large amount of light reflected back is due to this.
Once you understand the principles involved you'll realise why all exposure algorithms will always have limits.
Hope this helps.
Yours,
David
Thanks David,
I have also noticed something very strange. Now the max sync speed of the 5DII is 1/200 before you need to use HSS. However, if you have the camera in manual mode and the flash in manual, the max sync speed is reduced to 1/160 if you also have the HSS button pressed. It shouldn't really be kicking in until 1/250 right? I have no explanation for this. Have you come across it or any ideas?
Thanks again
Hi Mark,
If you have both the camera and Speedlite in manual then there is no minimum shutter speed with FP-mode (high speed sync) enabled (as opposed to the 1/160s that you mention).
If you weren't in FP-mode you would expect to be limited by a X-sync speed of 1/200s (not sure where 1/250s came from).
I've just verified this with a 5D Mark II and 580EX II. For me the flash sync speed is 1/200s in all modes.
With the camera in manual mode I can set a shutter speed of 1/200s (but no less) if the Speedlite is in normal mode, as opposed to FP-mode. It makes no difference if the Speedlite is set to manual or E-TTL. As soon as I switch the Speedlite to FP-mode I can access faster shutter speeds.
Not quite sure how you've managed to generate these results!
All the best,
David
Hi David,
Sorry I seem to have phrased my question poorly.
Yes I confirm in all modes without HSS button pressed you can dial a shutter in up to 1/200 only.
My confusion is that if you take a picture with your shutter at this speed in ETTL flash - you will get the same flash exposure if you have HSS button pressed or not.
However with the flash in manual mode if you turn HSS on or off at 1/200 you get two different flash exposures - one much brighter.
Now turning your shutter down to 1/160 and try that again and you get two identical exposures.
To me this implies that HSS is having an affect at 1/200 when it should not be until you go to a faster shutter speed.
Does that make sense? This is really confusing me :)
Hi Mark,
That's clearer!
I put my 5D Mark II and 580EX II in manual mode. With shutter speeds slower that 1/200s it made no difference if the flash unit was in FP-mode or not. With a shutter speed of 1/200s, however, the 580EX II was adding less light when in FP-mode.
What this obviously means is that at 1/200s the Speedlite is actually using FP-mode (which reduces flash output) even though it should be able to sync fully with the shutter.
Very odd!
All the best,
David
Thanks for confirming!
I've looked all over the internet and never seen this reported or explained. A first on your blog :)
Thank you
Hey David me again...
Now I'm noticing some behaviour I don't understand on my 5D2 and 580EXII: If I expose a scene in AV
mode so the meter scale rests on 0 (for example), I then take the same ISO/shutter/Apperture
readings into Manual mode - but if the 580EXII is on the camera EV meter now shows -1.
So in AV mode the ambient exposure is always -1 stops?
If you turn the flash off - AV mode will then meter ambient same as Manual mode.
Any ideas why?
regards
Mark
Hi Mark,
I think this must be the E-TTL algorithm in action.
E-TTL has to balance flash and ambient light and decide whether the flash serves as key or fill light. It often tends to underexpose for ambient light. The addition of flash then 'tops up' the exposure - and you now have your light where you want it!
Does this make sense?
All the best,
David
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