Low Light Photography
Digital imaging has revolutionized the possibilities by giving photographers a third dimension to work with: light sensitivity.
Film is a challenge because it is generally works at ISO 100-400. If you opt to underexpose you can push two stops higher, but at the cost of shadow detail. For these reasons shooting in low light requires some creativity.
Medium format cameras provide a larger "sensor" size, but for low-light photography this may yet another challenge because a larger focus area of require a higher aperature to gain the same depth of field for a given field of view:
The critical realization here is that a larger format gives you the ability to capture a larger part of the scene, but you cannot get closer without more light—the amount of light required for a given sq. mm of film is a constant.
So you cannot alter physics, but for low-light photography a larger format still gives you a profound advantage: to achieve the same depth of field you will need to back away from the scene (or use a wider lens), but now you don't need to be as careful about framing! Get the subject in focus and crop it later.
The Shutter-Release Rule
I typically meter for portraits at ISO 200, which means that even heavy cloud clover begins to limit the shutter speed. I know that some photographers like to test the limits of how slow they can hand-hold a camera, but hand-holding a medium format camera blow 1/125 is very hard to achieve.
Landscape photographers have long observed that slower shutter speeds are even difficult to achieve with a tripod because pushing the shutter release jars the camera slightly. The same phenomenon can be observed when scanning film with a macro adapter. Indeed it is nearly impossible to get a sharp image without using the self-timer. For this reason I use a shutter release cable in all conditions.
While I have always had a shutter release cable, it's value was slow to dawn on me.
In an environment with limited contrast, such as indoors under florescent lighting, go ahead and underexpose by two stops and then push-process by leaving it stand in the developer longer. Pushing does not increase the speed of the film, so why not scan an underexposed negative? Scanning (or printing) from an underexposed negative that is processed at normal times is an option, but push processing boots contrast chemically, which is a different look.
ISO 100 color reversal film also pushes without noticeable color shift, so on overcast days I will rate it at 200 without a second thought.
If you need to shoot with the lens wide open it is imperative that you have a camera which gives you the ability to focus on any point in the frame. Frame the shot, then focus. This could be called The Tripod Rule because a tripod allows you to maintain framing while you work to achieve the correct focus.
There is a technique called “focus and recompose” which is unintelligible to me. The focus plane is flat, not a curve! Hence rotating the camera after focusing on the center will put the subject behind focal plane.
645, HP5+ rated at 400