just a quick question.I am shooting a video soon and have been to the location to do a few camera tests.Its in a gallery space where the light is quite bright inside.I used my lightest ND filter but found the exposure a bit to dark and i want to keep as wide an aperture as possible for a shallow depth of field so my question is this...i'm aware that that adding gain will introduce noise into the picture and was just wondering if i brought the gain down,be it -3db or -6db to bring the exposure down,does this also introduce noise or is it only when you add gain?
Think about it for a second, and then trust your instincts; if adding gain (+3, +6, etc) increases noise, then subtracting gain (-3,-6) must....reduce noise. Correct. What is really happening is that the sensitivity of the green channel is changing and to compensate for proper white balance, the red and blue channels must gain up or down to match, the rub is that as blue gain increases so does the noise. Of course there is no free lunch, as you subtract gain and get a "quieter" or more noise free picture you get less dynamic range in the highlights. Some cameras must even gain up to -6Db to get their fullest dynamic range, so be careful. If you're looking for extended dynamic range to accommodate detail in darker darks and brighter whites then use Nd filters rather than minus gain to control your iris to wide open.