A quick question- is there a way of locking the exposure (EV) on 5D MkIII in Manual mode?
For instance, if I set my exposure to f/8 and 1/250, is there a way of going to f/4 and for the camera to go to 1/1000? (I mean from turning the main dial only?)
Thanks!
There's no such functionality with the 5D Mark III.
The 7D Mark II and 5D Mark IV (and maybe other newer models) have something almost like what you're asking. If you 1) swap lenses to one with a narrower aperture, 2) add an extender (which raises the maximum f-number), or 3) use a zoom lens at a focal length that has a narrower maximum aperture than what the camera is set to in Manual exposure mode then the camera can alter either the shutter speed or ISO value to compensate. There is a custom function option that allows the user to disable the feature, use ISO to shift, or use Tv to shift.
With the 5D Mark III the closest you'll get is to use Program mode. To alter exposure you can use the Quick Control Dial on the back of the camera to set Exposure Compensation. You can lock in a particular EV by pressing the AE Lock button (the button next to the AF-ON button marked with an "*"). You can then shift Tv and Av in opposite directions by moving the Main Dial just behind the shutter button.
If you press and release the AE Lock button, as long as the viewfinder is active the camera will maintain the same EV as you shift through various combinations of Tv and Av. Once the viewfinder becomes inactive or you press the shutter button all the way down to take a picture the EV is reset the next time you initiate metering or AF to activate the viewfinder. You can also press and hold the AE Lock button to keep metering active and maintain the same EV indefinitely (or at least until the camera's battery is exhausted). The locked EV will be maintained for as many frames as you choose to take while holding the AE Lock button.
You can also choose one of several metering modes that may get the initial Exposure Value selected by the camera closer to what you want. Spot, Partial, and Center weighted average metering modes will move progressively from the smallest spot in the center of the frame to the largest area. Evaluative Metering uses a library of scenarios to determine which area of the frame should be neutrally exposed.
P mode can achieve this to some (large) extent. The exposure is locked, but aperture and speed can still be adjusted. They cannot be adjusted independently. The overall exposures will stay the same.
To start with some exposure that's different from what the meter reading was, you'd have to do that with exposure compensation. This limits the overall exposure level that you can choose that it cannot be very far away from the meter reading, because exposure compensation is limited to some offset from the meter reading, usually +- 2 or 3 stops.
If you want the camera to change the shutter automatically in relationship to the changes you make to the aperture then use the camera in aperture priority mode and the shutter will change automatically when you change the aperture. Or the inverse it true, if you want to use a specific shutter speed to stop motion then you would use shutter priority mode, choose the shutter speed and then if you decide that the speed you chose is not fast enough when you change to a faster speed the camera will compensate accordingly. In both cases if you use the exposure compensation ( say plus 1/3 stop ) the camera will maintain the setting of the mode you are in ( the aperture or the shutter ) and change the other to keep the exposure compensation you have set.
The point of being in manual mode is that your brain makes the decisions and you control the camera. if you know you made a two stop adjustment to the aperture then you can quickly make a two stop adjustment to the shutter speed using the handy buttons at your fingertips.
A quick question- is there a way of locking the exposure (EV) on 5D MkIII in Manual mode?
A quick answer: No.
The Av and Tv modes adjust shutter speed and aperture, respectively, to provide a proper exposure given your chosen aperture or shutter speed, respectively. And you can use exposure compensation to change the level that the camera considers "proper," but both these modes (and P mode as well) rely on the metering system. You seem to want to set some arbitrary combination of aperture and shutter speed and then lock them together, so that they change inversely, i.e. +1 stop of aperture would be compensated for with -1 stop of exposure time and vice versa. That's not a feature that's available on any mainstream camera that I know of.
