Why the shutter is in the lens

Two ways to make a shutter

A shutter lets light reach the film for a measured moment. There are two common designs.

A focal-plane shutter sits in the body, just in front of the film: two curtains, one opening and one following it to close. At slow speeds the whole frame is uncovered at once. At fast speeds the second curtain starts before the first has finished, and a narrow slit races across the film. It's how most 35 mm cameras work, and how the first Hasselblads worked too, until their thin steel curtains kept breaking.

A leaf shutter sits inside the lens: a ring of thin overlapping blades that swing open from the center and close again. At every speed the whole frame is exposed at once. That's the shutter in every lens on your bench, and you can see its blades close when you look into the front of a lens and fire it.

What the leaf shutter gives you, and what it costs

The big gift is flash at every speed. A flash lasts a tiny fraction of a second, so the whole frame has to be uncovered at that instant. With a focal-plane shutter that only happens at slower speeds, before the slit begins. A leaf shutter is fully open at every speed up to 1/500, so you can use flash in daylight to fill in shadows, at a fast speed, which made the Hasselblad a favorite of studio and wedding photographers. Leaf shutters are also quiet, and they can't distort moving subjects the way a traveling slit can.

The cost is speed and complexity. A leaf shutter's blades have to start, open and stop, so the top speed is 1/500. And every lens has to carry a whole precision mechanism of its own, so the lenses are more expensive, and each one needs servicing separately. When a 503CX's slow speeds start to drag, it's the lens that goes to the repairer, not the camera.

Why the body needs a second shutter

To let you see through the lens, a leaf shutter has to stand open while you compose. So does the aperture, which stays wide open to give you the brightest screen. But with the lens open, light would pour onto the film. So the body has a second shutter of its own: two rear blinds behind the mirror. They don't time the exposure. Their job is simply to keep the film dark until the lens is ready.

That's what makes the firing sequence you watched in slow motion so busy. When you press the release:

1. the lens shutter closes, and the aperture closes down to your setting;
2. the mirror swings up out of the way;
3. the rear blinds open;
4. the lens shutter opens and closes: that's the exposure.

Then everything waits. The mirror stays up, so the finder is dark, until you wind. One turn of the crank closes the blinds, lowers the mirror, reopens the lens, moves the film on and cocks the shutter, all at once.

Every lock has a reason

Because the camera comes apart, and because body and lens each hold half of the mechanism, the order you do things in matters. The 503CX enforces it with locks. Each one is protecting your film, or the camera itself:

None of these is a fault, and you can always get out of them: you've done each one on the bench. The camera's refusal is information. When something won't move, ask what state the camera is in, and the answer is almost always one of the six above.

The jolt, and the habit that beats it

The 503CX's mirror is large, and it swings up hard. The jolt is enough to soften a picture at slow speeds, even on a heavy tripod. Photographers fight it with three habits that work together: a tripod, a cable release so your hand isn't on the camera, and the pre-release, which lifts the mirror early so its jolt has died away before the shutter opens. Ansel Adams used exactly this combination for Moon and Half Dome in 1960, with a 250 mm lens, where the slightest shake would have shown.

Reading the lens

A CF lens has three rings. The front one focuses. Behind it are the aperture ring and the shutter-speed ring, linked by an EV scale and a small cross-couple button. Press the button and the two rings turn together, so that as the aperture closes a stop, the shutter slows a stop, and the exposure stays the same. Meter once, couple the rings, and choose the pair that suits the picture.

Behind the focusing ring is the depth-of-field scale: pairs of marks for each f-number, either side of the focus index. Whatever distances fall between the two marks for your aperture will be acceptably sharp. Set infinity against the far mark for your aperture, and everything from the distance at the near mark out to the horizon will be sharp. That's hyperfocal focusing, a landscape photographer's trick when the screen is too dim to judge.