Synchronized swimming for photographers

Strange as it may seem, there are some similarities between synchronized swimming and photography. One is that photographers love to shoot the virtuoso performances of athletic swimmers, but there's something else, much more important. This is the necessity, both in synchronized swimming and in photography, for certain things to happen at a precisely defined moment. Let's leave swimming alone and focus on another type of synchronization - between a camera and a flash. In this article, I will address some basic questions related to triggering and synchronizing studio flashes.

Actually, what is this synchronization?
Very simply - when shooting with a flash, it must be triggered at a precisely defined moment. More precisely, it must be triggered when the camera's shutter fires. And even more precisely, when the shutter has fully opened the frame. This is possible at so-called sync speeds.

Sync speed, what is that?!?
Here I need to start from a broader perspective. From the design of the focal plane shutter, which is found in practically every single-lens reflex camera (SLR or DSLR). We call it that because it is located directly in front of the focal plane. The focal plane is the plane (digital sensor or film) onto which the camera's lens projects the image of the objects we are photographing. This shutter consists of two curtains. When it is triggered, one curtain retracts and opens the frame. After it, and after a certain time interval, the second curtain unfolds, which in turn closes the frame. When the shutter is charged, the two curtains together travel back this path and return to their original position. When the shutter is charged, the curtains are tightly closed together, preventing light from reaching the focal plane. When operating at certain speeds, the second curtain is activated only after the first has completed its path and fully opened the frame (see animation bottom left). This is the moment when the flash should be triggered, as its impulse will then be able to expose the entire area of the frame. Shutter speeds at which the frame is fully open are called sync speeds. On the other hand, when operating at shorter exposure times, the second shutter curtain is triggered before the first has completed its path (see animation bottom right). This creates a narrow slit that passes through the focal plane, and thus the light impulse of the flash cannot expose the entire frame.

   see animation                                               see animation

How to trigger the flash?
By closing its triggering circuit. This is done via the camera's sync contact, which is activated at the right moment when the shutter fires. The contact can be electromechanical or the circuit can be closed electronically, working with optical or other sensors. Most latest generation cameras use the second option. To close the control circuit at the right moment, there must be communication between the camera and the flash. This can be done in three main ways:

Triggering studio flashes via sync cable
This is the most reliable and at the same time the most inconvenient way to connect the camera to the studio flash. The reliability comes from the fact that this way we get a direct galvanic connection between the two devices. On the other hand, the cable constantly connected to the camera (and flash) requires us to be aware of its presence - not to step on it, not to trip over it, not to knock something over. The length of a standard sync cable is in the order of 4-5 meters, which in some situations can be a limiting factor. Using a cable to connect the camera and studio flash is recommended mainly for shooting static shots, such as product photography.

At one end, the sync cable is equipped with a special jack that plugs into the studio flash. Two main standards are used - 6.3 mm and 3.5 mm (see image on the left). Some products use a 2.5 mm standard, but this is rare. By itself, this is a common mono jack, also used in audio equipment. All sorts of adapters between the described sizes are available on the market.

More important is the other end of the sync cable. There is the so-called PC (pi-cee) connector. This abbreviation has nothing to do with "personal computer" and comes from the names of camera shutter manufacturers Prontor and Compur. It can be plugged into a special socket, which practically all professional cameras have (see image bottom left). Some mid- and low-end models do not have such a possibility, but the problem is easily solved by an adapter (in the image bottom right), which is placed in the hot shoe for a manual flash.

Triggering studio flashes via radio trigger
The radio trigger consists of two parts - a transmitter, which is placed on the camera, and a receiver, which is connected to the flash (see images below).

This is the most convenient way to trigger studio flashes, as it eliminates the sync cable, which creates many inconveniences. The range of most such triggers is about 30 m, which is also a great advantage. These devices usually have several working channels. This is especially useful in cases where two or more photographers are working with studio lighting close to each other.

The receiver can be self-powered (batteries) or connected to the studio flash's power cable. The first option is mandatory when working with portable generator lighting, while the second is used in the studio. One transmitter can work with an unlimited number of receivers, provided they are of the same model and set to the same channel.

In addition to their undeniable advantages, radio triggers also have some disadvantages. The main one is that interference can occur in their operation near some powerful sources of electromagnetic radiation. In general photographic practice, this happens extremely rarely, but if we find ourselves in such a situation, we can use the sync cable described above. Another disadvantage of radio triggers is the slight delay in signal transmission from the transmitter to the receiver. This phenomenon limits the use of 1/250 sec as the shortest sync speed, but in most cases we can safely work at 1/200 or 1/160 sec.

There are high-end radio triggers on the market, such as PocketWizard and similar devices, which have eliminated the disadvantages described above. They are not affected by sources of interference because the connection between the transmitter and receiver is digitally coded. The shortest sync speed is 1/500 (with cameras with a central shutter), and the range is over 500 meters. They also have many other features that are difficult to list in an article like this. The only disadvantage of these devices is their high price.

Triggering studio flashes optically

Practically every studio flash has a built-in photosensor, more popularly known as a "photocell". This is an optoelectronic device that triggers the flash when it "catches" an impulse from another flash. A lighting setup usually consists of two or more flashes. One of them is chosen as the main flash and is triggered using a radio trigger or sync cable, as described above. The other flashes in the same setup are triggered via their built-in photocells.

The built-in photocell is a device that plays more of a supporting role when working with studio lighting, but in some cases, it can be the primary device that triggers our flashes. For example, when for some reason we do not have a sync cable or a radio trigger. Then we can use the camera's built-in flash or a hot shoe flash. For this purpose, we need to reduce its power so that the strength of its impulse does not affect the lighting setup, but is still sufficient to trigger the studio flashes via their built-in photocells.

In photographic practice, there are situations where we cannot rely on the photocell. For example, when working outdoors, in very large rooms, or other environments that absorb a lot of light or interfere with its dispersion. In these cases, the light from the main flash will not reach the photocells of the other flashes. We can solve the problem by using a radio trigger and mounting a receiver on each flash.