You are right, EV is a 3 component parameter. I'm sorry but I have to say that shutter speed is a variable parameter on SJ5000x. Many times I (and many people) use ND filters to lower the shutter speed on cams that don't have the option to select shutter speed to obtain a less crispy footage. http://www.thehdpilot.com/blog-article.aspx?id=62 So, if Aperture is fixed, changing EV modifies 2 parameters: Shutter speed & ISO. In a low light situation the Shutter speed is lowered and ISO value goes up, if ISO is too high you'll have lot of noise. If yo can limit ISO value you'll get a darker footage but less noisy.
Ok, I did my tests in a rather dim room and maybe therefore the shutter speed was already set to be slowest possible (Low Light Mode was OFF) and therefore applying an EV correction changed only the ISO?
Yes it's possible, I don't know exactly what rule follows the camera to give priority to ISO or Shutter Speed when adjusting values. I you (we) should have control limiting ISO you control the camera not going to high ISO values and control noise.
