How to use ND filter for DSLR filming

The old way was to have allot of ND filters and had to change it each time the conditions changes. But that was cause you didnt want to change the ISO of the film each time, which meant you had to change the whole film roll. But with the new DSLR you can take advantage of the ISO and use an actual slightly too dark ND filter and add ISO to brighten it, while keeping a wide aperture with a slow shutter speeds. What it also does most wide aperture lenses actually have problems when used wide open they give a soft glow at over exposed areas. But having the lighting slightly under exposed makes the soft glow go away and amping the iso help you getting the light back and able to film wide open while it is sunny plus removing some problems of the lens.