walter_remson

You may have forgotten that the Instant Color Film that you are using is ISO 100 and that your camera is setup for a different ISO setting: i.e. ISO 160, 320 or 400. I have done the same thing when checking exposer before taking a picture with Instant Film. So I do not use the Instant Film to test exposure unless the film in the camera is the same ISO number (not likely because most of the film I have is faster than ISO 100). I believe the information given about using a Guide Number divided by the distance will give "Good" results (maybe not excellent). If you are using 220 film you can always bracket (0, +, -) the picture you are taking.