I understand the general rule of thumb is to use a shutter that is the inverse double of your frame rate. For instance, if my frame rate is 30fps I should use a shutter of 1/60s. My question this: If I need more or less light for proper exposure, am I better off shooting as close to 1/60s as possible or should I always work in multiples of two of my frame rate? (Example: should I use 1/50s since its closest to 1/60s or should I use 1/30s since its a multiple of 30? I understand that I could adjust ISO but in most cases I prefer to leave it at 100 or 200 to minimize noise/grain. Thanks!!