It depends on how you want to work. You could set the ISO on your camera to 12 and meter without the filter, which would give you the correct exposure once it's in place. Whenever I've used SFX I've used a hand held meter set to ISO12 so if you set your camera the same it's effectively doing the same thing. Alternatively you could leave the ISO at 200 but you'd need to remember to increase exposure by 4 stops. Either way will give you the same exposure, it just depends what you find easiest. As a guide in bright sunlight outdoors you'd be expecting to use exposures of around 1/8 to 1/30 at f11. As your filter's opaque your camera may not be able to meter through it like it would a standard red filter in all lighting conditions, and it would be more or less impossible to compose and focus through it. As mentioned above if you do set the ISO to 12 leave the exposure compensation alone, you shouldn't need it. Any more queries just ask.