I have an idea for a shot I would like to try but could use some clarification on layering. The image would ultimately be an action shot composed of two different exposures. One would be shot at a very low shutter speed. This one would be the background. The second shot would be at a faster shutter speed in order to freeze the action. If all I want from the second shot is the frozen action how would I go about layering them and taking only that part? Some careful cropping/erasing? Searched for tutorials but couldnt find any. Seems like it should be fairly straightforward but Im having trouble thinking it through. Thanks for any help.