I am using a Canon 5D MKIII. I take a lot of low-light fotos and want to achieve low DOF while keeping the photos sharp with fast-moving subjects (musicians), using a 5mm 1.4 lens. So far, I always did this with TV mode and automatic ISO. I stopped down 1 step to get photos that have the same brightness as what I actually see.
Now the issue there is that sometimes, there is enough light so that the camera switches to a higher aperture and I lose the low DOF.
I thought if I switch to manual mode and fix the settings at 160th/F1.4, I can avoid that. But then, the automatic ISO brightens up the photo again and takes the images at a unnecessary high ISO.
How can I avoid that? How can I fix the settings in speed and aperture but tell the camera not to try to make the picture brighter than reality by choosing a too high ISO?
I do not want to use manual ISO on top of the other settings fixed since the light changes quite quickly depending on my position and I am not fast enough to change the ISO.