I took a number of ambient light portraits on Friday and I'm a little disappointed by the amount of motion blur (not camera shake) on parts of the subject. Altering the lighting was not an option.
I was using a 50mm f/1.8 lens and shooting at f/1.8 in aperture priority mode. My Canon EOS 5D Mk II was frequently setting the shutter speed to 1/40 or 1/50 of a second, and this was quite often not fast enough to stop blurring of the subject. Even the gentle swinging of an earring was causing blurring at 1/40, and small movements in the head or hands would make an otherwise nice shot disappointing.
My question is: how do you force the camera to use the desired aperture, and also specify a shutter speed of at least (say) 1/125 of a second, forcing the camera to use a higher ISO (if necessary) in exchange for a faster shutter speed?
[In case it's of interest, a typical exposure from this scene was f/1.8 for 1/40 at ISO 200.]