So, this problem has come up from working in nightclubs, where I am trying to get a night exposure for a human subject in the foreground, but have a shutter speed of around 1/30 or so for the ambient background.
I have toyed around with a couple of variations, each coming close to what I would like, but nothing bang on the nail.
Ideally I would like to have control of my aperture and shutter speed, and have the camera work out the ISO for me. The first problem I encounter is once I have mounted my flash (as this point I feel I should talk equipment. 5D3, 16-35 MK2 L, 24-70 MK2 L & EX 580 2) the auto ISO options become constrained. I have read into this a little, and have found a couple of ways around it.
Option 1... I set my ISO 4000, I set the shutter speed 1/60-1/200 and get the choice of aperture I want. Fine, except if I don't want my ISO higher than 4000, but I do want my shutter speed a little longer, say around the 1/25-1/30 mark.
Option 2... I set the Shutter speed to whatever I want 1/30 or whatever, have the auto ISO on (normally locked out at 400 max) but with the safety shift on ISO, with the ISO parameter set to a max of 6400. The problem with this is I don't like having the lens wide open. Drunk people in clubs tend to sway, and the fine depth of field result, inevitably, in people swaying out of the sweet spot. Plus on the 16-35 f4 is noticeably sharper than f2.8.
Option 3... I set the aperture at f4 on Av mode, and have the minimum time value parameter set to 1/30. This seems to work perfectly, until you switch on the flash, at which point, it forgets all about the 1/30 minimum shutter, AND locks out the flash to ISO 400.
Can anyone think of a way to have my minimum aperture set to f4, whilst I retain control of the shutter speed, and have the auto ISO range up to 6400 (or at least higher than 400!)
Sorry if this seems a trivial question, but I can't for the life of me figure it out.