Unlocking the secret symbol: How a crossed-out circle on your camera can enhance your photography skills

Almost all digital cameras with interchangeable optics display a symbol that looks like a crossed-out circle. This symbol isn't a contemporary feature but was already seen on film devices. Usually found on the upper part of the camera body, it can also be located on the casing around the viewfinder. It's about time we unravel the mystery behind this symbol and explain its purpose.

The crossed-out circle symbol is akin to the Greek letter "Phi". It indicates the spot where the light-sensitive matrix or plane of traditional light-sensitive material resides. This is the exact point where the light rays, having passed through the lens, land. Aside from being informative, this symbol also has practical applications.

With the proliferation of advanced mirrorless cameras, lenses with quick and accurate autofocus are at the helm. However, in some photography niches, like macrophotography or reproduction photos, manual settings are more effective. This is where the "Phi" symbol truly shines.

For achieving optimal sharpness, it is necessary to measure the distance between the symbol and the chosen point, and then establish this value on the lens scale. Of course, a precondition for this is the presence of such a scale on the lens. Sadly, many current designs no longer feature it, with the element often regarded as obsolete.

While modern photography leans on autofocus lenses, the landscape changes for movies. Most film productions prefer manual focus settings, and measuring the distance from the light-sensitive material to the object with a ruler is a routine practice. On a film set, the person in charge of setting the focus is the "sharpener", typically the first assistant to the camera. Referred to as the "focus puller" in English, this crew member is crucial for dynamic shots where continual focus adjustment is needed. The sharpener must be highly skilled and possess exceptional vision.

Beyond its practical application in photo creation, the symbol on top of the camera serves another role. This symbol allows for precise calibration of lenses, which is sure to be appreciated by enthusiasts of independent optics manufacturers like Sigma or Tamron. In order to do this, not only does one need to measure the distance from the object, but a correction must also be made in the lens' software, achieved through a specially designed docking station.

Back when digital SLRs were predominant, almost every owner of independent optics had such a docking station and calibrated their lenses on their own. Nowadays, the designs for mirrorless cameras are so precise that calibration is seldom needed.