The Shutter

Diaphragm shutters, which for every other purpose are preferable, scarcely enter into competition with the focal-plane shutter for instantaneous work at high speed. With no other "back" shutter can one be quite sure that the two movements which control the raising of the mirror and the rapid exposure of the plate have been successfully accomplished. No other shutter has been brought to so high a degree of efficiency during the last few years.

But beware of old-fashioned, second-hand, focal-plane shutters. Some are quite an inch away from the actual focal plane and create a sort of fog. And some operate with a jerk that may even affect the picture at low speeds, and will at any rate advertise the presence of the camera to every living thing within fifty yards. A cheap reflex with a cheap focal plane is worthless. To do good instantaneous work get one of the very latest patterns in which the multitude of cords, winders, hooks, and sliding knobs are done away with and, if possible, the tension springs as well. A single winding key should control all movements as in the old-fashioned Thornton Pickard shutter. Have the shutter tested for speeds at the earliest opportunity, to be sure that they are really attained by the instrument, or are purely arbitrary.

The intergearing of mirror and shutter should be such that when the mirror is shut up the shutter cannot be wound, and so expose the plate accidentally. Perhaps it is still better to demand a self-capping blind.

Our remarks about diaphragm shutters, however, require some modification. Since the time when this chapter was first written, two high-grade reflex cameras of great practical efficiency have been introduced, both equipped only with the diaphragm shutter, and one of them with the multi-speed shutter - probably the fastest in existence. But one great advantage of the focal plane remains still unchallenged, viz. that it permits of nearly double the amount of light reaching the plate in fast exposures with the lens at full aperture. There is a considerable loss of light with diaphragm shutters when working with a lens at any stop wider than f/8.

Size Of Camera

The worst of a well-equipped reflex camera is the size and weight. It is a cumbersome article on a tour, even now that an excellent folding reflex is on the market. A quarter-plate camera is as large as can be managed by the ordinary man; in fact we do not see why it will not serve for press purposes, seeing that an enlargement can be made as quickly as a contact print; 5 x 4 in. is certainly the most formidable reflex camera that we should care to be burdened with, and its weight is half as much again as the quarter plate.

The Higher Speeds

A focal-plane shutter usually includes beyond the 1/100, 1/200, 1/400, 1/600, 1/800, 1/1000 sec. And a few calculations will show that in purely instantaneous work within a few feet of the plate these high speeds are frequently called into action. A man walking only three miles an hour moves 4 1/2 ft. per second. During that second his image will have travelled across the focussing screen if he is within, say, eight feet of the lens. A trotting horse is estimated to move through 39 ft., and a galloping horse about 50 ft. Express trains (not to mention birds, whose flight is at a speed treble that of the locomotive) soon exhaust the capabilities of a shutter at 1/1000 sec.

In photographing rapid motion at athletic sports, races, and the like, the subject is, if possible, taken when approaching in the direction of the camera, and not crossing the field of view at right angles. The range of pictures at a comparatively low speed may be thus considerably increased - an important matter when the weather is dull and the light in consequence rather weak.

If the speed of a shutter to take an object moving at a given rate has to be estimated, the distance of the object must be divided by 100 times the focus of the lens, and then the rapidity of motion of object must be divided by the result. Or if R be rate of motion of the object, D the distance and F the focus of the lens, then, in order that the circle of confusion may not exceed 1/100 inch, s= D

100F x R.

The subjoined table will give a few suggested speeds for the shutter, gathered from our own experience or from reliable sources. These speeds have no reference whatever to the light conditions prevailing at the time of exposure. In the A column is given the figure for objects in motion parallel to the direction of the camera; in B, objects crossing the field of view at right angles.

A.

B.

sec.

sec.

Street scenes (no apid motion) ....

1/10

1/30

,, ,, cart traffic.....

1/20

1/60

Animals grazing, birds feeding ....

1/15

to 1/20

Man walking three miles an hour

1/30

1/90

Children building castles, paddling, etc.

1/30

to 1/60

Coaches, six miles an hour.....

1/60

1/180

,, ten ,, ,,.....

1/100

1/300

Cyclists (not scorching).....

1/150

1/500

Galloping horses......

1/300

1/900

Large birds flying, ducks, gulls, etc. .

1/300

1

Athletic sports.......

1/300

1/1000

Small birds flying......

1/600

These speeds are calculated for a point about 50 times the focal length in distance from the lens. For nearer points the speed of shutter must be increased in proportion. For instance, a child skipping at, say, 25 ft. from the lens would probably give a sharp image at 1/60 sec.; at 8 ft. from the lens the highest speed of the shutter would perchance be vainly called into operation.

With many subjects there is a critical instant when a successful snapshot may be taken at a comparatively low speed and yet convey the most vivid impression. For instance during a high jump, and still better in skipping, motion is actually less just when the athlete is attaining the full height of his leap, and before he has commenced his descent. We have seen a capital picture of a batsman's middle stump falling, which was taken at 1/100 sec.; the ball is not very sharp, but could easily be touched up, and is, after all, a minor consideration.

Arrested Motion

In the hands of a master, like Mr. Adolphe Abrahams, and particularly in the portrayal of incidents occurring at athletic sports, rowing contests, and yacht races, the records of the instantaneous shutter sometimes rise to the dignity of true pictures. More often they are merely triumphs of a highly perfected instrument. We are shown snap-shots of an express train travelling at sixty or seventy miles an hour; the spokes of the wheels are all sharply defined; there is no sign of motion whatever. We might be gazing at a stationary locomotive engine discharging smoke in a high wind. Leaping horses look as if they were paralysed and hanging in the air by invisible wires; the winning eight have apparently posed themselves rather awkwardly after splashing the water somewhat. Portraits of ladies skipping are exceedingly uncomplimentary; their mouths are generally wide open and their whole aspect displays little of the grace of motion. We sigh for the old-fashioned sporting print. For this is a field in which the camera must fail in nine cases out of ten. The successive action of the muscles as each is called into play cannot be recorded on a single instantaneous plate; and we must be content to leave the artist to express motion conventionally, or resort to the continuous record on the cinematograph.

Guy's Mill, Warwick.

Guy's Mill, Warwick.

F. Low.