I am wanting to buy a 405 film back for exposure tests and am worried because I am most often shooting at very low light conditions where my exposure time is a few seconds. I will be using Velvia mostly and want to know if the color films for the back can handle at least a second or two of exposure time. I have heard that the Polapan might work, but I am afraid it may be hard to judge color work from a B&W test print in the flat light I am working in. I would like to hear what others have top say about this. Thanks in advance.