The Pin-Registered 4ER Camera
The optical path of the 35mm 4ER camera is similar to that of most other pin-registered cameras, except the camera employs a beam-splitter. This beamsplitter is essentially a very thin partial mirror that splits 25 percent of the light to the eyepiece and allows 75 percent to continue to the film plane.

A disadvantage of this method is that you lose 1/2 stop of light to the film. An advantage, however, is that you are able to use a shuttered video camera for video assist, which gives you much sharper images. As a result, you can analyze your shots much more accurately. Because fast-moving objects are nearly always shot with this type of camera, the shuttered video tap is an absolute necessity.

This method of reflexing is also preferable when shooting high-speed cinematography with Unilux strobes. You only have to flash once per frame. Your film receives 75 percent of the light, and your eye sees 25 percent.

Cameras that employ a spinning mirror must flash once for the film and once for the viewing system. A 300-fps spinning mirror camera requires the strobes to run at 600 flashes per second, which substantially reduces the output of the strobe (about two stops).

An alternative is the use of a split-sync system, which synchronizes one light head 180 degrees out of phase of the shooting heads. This method’s drawback is that the camera operator and video assist system do not see the actual light that will be exposing the film.

Most objects fall at a rate of approximately 32 feet per second squared. After falling 18 inches, an object will be traveling at a speed of approximately 117 inches per second. As the object continues to accelerate, it will go through a two-inch field of view in approximately 1/100th of a second. Using a camera speed of 2,500 fps, this equals about one second of screen time, depending on your transfer rate.

On the other hand, if you use the same field of view and frame rate, but drop the object only two inches before it enters the frame, the calculated time to travel the next two inches is approximately 4/100ths of a second (.04 x 2,500 fps = 100 frames). Therefore, the result is four times the screen time (four seconds). This basic law of gravity is many times overlooked or underestimated on the set.

Unilux Strobe Lights
Unilux strobe lights, often used with pin-registered high-speed cameras, have some great advantages over constant light. The biggest asset is the short exposure time of 1/100,000th of a second. This exposure duration gives you an extra degree of sharpness that is almost impossible to obtain by simply reducing the shutter angle in the camera.

You can increase sharpness by reducing the camera shutter angle when using constant light. But to obtain proper film exposure for an equivalent exposure time of 1/100,000th of a second, you would be forced to work in light levels that would most likely melt your product and/or your set.

Another advantage of the strobe is that the intensity for which it is adjusted remains constant. The strobe is a short-duration pulsed light that is triggered at the mid-opening of the shutter. Consequently, the exposure time remains the same, regardless of the frame rate.

Synchronizing the Strobes to the Camera
Synchronization of the strobes and 4ER camera is fairly simple:

● Connect the sync cord supplied by Unilux

● Turn the camera on at the frame rate you will be running

● Point the strobe into the lens port or at the movement drive coupling

● Adjust the time delay on the strobe system to fire not only when the shutter is open, but also when the register 
   pins have reached their apex and are beginning to retract (slightly retarded from the mid-shutter point).

The reason for this is that the film has been registered and is now in a relaxed state. This also gives the vacuum-assisted gate enough time to draw the film back against the pressure plate. Because the 4ER uses a beam-splitter to reflex the camera, only one strobe firing per frame is required.

As discussed earlier, if you are using a camera that employs a spinning mirror for reflexing, then you must flash once for the eye and once for the film. Viewing through the lens port during synchronization should reveal a double image. One image will be the camera aperture with the leading and trailing edge of the shutter equally spaced above and below the aperture. The other image will be the ground glass. If questions regarding synchronization arise, do not take any chances. Call the nearest Unilux representative for help.

Metering the Strobe
The most common meter used in conjunction with the Unilux strobes is the Minolta 4. Reading the strobes is relatively simple:

● Set the meter to 1/60th of a second in the ambient mode.

● Set the strobe system in the meter mode, which gives you 60 flashes per second at shooting intensity.

● Push the meter button and take a reading.

Because the meter is sampling 1/60th of a second, you have just read the intensity of one flash, which is what each frame will be exposed with when properly synchronized to the camera. It is common practice to sample the light several times to ensure that the meter received a full flash. The only compensation between the meter and the f-stop would be opening 1/2 stop for the beam-splitter, if applicable.

Although the strobe system seems to become brighter as the camera comes up to speed, each flash remains the same intensity. It just seems to be brighter to the eye, because the number of strobe firings per second increases and your mind’s eye retains the many firings.

Mixing Tungsten & Unilux Strobes
I advise mixing in some tungsten light when shooting solids, such as cereal, small candies, coins or coffee. Because the Unilux strobe has an effective exposure time of 1/100,000th of a second, each frame is extremely sharp. Subjects in motion have no blur, which can result in a pixilated or chattering effect. This becomes more pronounced as the velocity of the subject increases.

The faster the subject moves, the farther it has traveled between exposures. Slower camera speeds accentuate the problem for that reason. Adding some tungsten light to the subject will add a tail or blur to the film, which helps blend one frame to the next. This also helps with the problem of “persistence of vision,” which is the ability of your eye to retain a previous image. In many cases, this appears as a double image when projected. But when analyzed frame by frame, the subject normally appears as a single sharp image.

The Use of Rigs
When shooting high-speed cinematography for commercials, you are usually shooting extreme close-ups. Although you may be in a soundstage that could have been used to shoot Ben-Hur, the camera, dolly, lights, rigs, flags, C stands and at least eight people invariably end up cramped in an area the size of a telephone booth. Between 5,000 and 20,000 foot candles light the area.

Then comes the time to ask your hand model or prop person to reach in there and drop those strawberries dead center in a three-inch field of view while holding depth of field of about 3/4 inch.

“And by the way, it’s about 200 degrees in there, so be careful not to burn yourself!”