Have you ever come across this alien-like symbol while cleaning or setting up your camera and had no idea what that was? Read further, where we discuss what this symbol is and its practical applications.

What Is That?

This symbol resembles the Greek Letter Phi (a circle with a line through it) and is usually found at the top part of your camera body. It is known as the focal plane mark or film plane mark. It is primarily used to indicate the position of the sensor/film inside the camera body. The position of the sensor/film is then used to determine the focal plane of your camera, where light rays coming from the subject going through your lens converge into a sharp image.

Practical Application of This Symbol in Photography

1. Practical Application of This Symbol in Photography

Minimum focus distance is not measured from the tip of your lens but measured from this mark onwards. This information allows you to figure out how close your lens can be to the subject and still be in focus. Therefore, it is very useful for macro and product photographers to make their necessary calculations to plan for their shoot so they do not bump into their subject when shooting.

2. Determine the Focus Distance to a Subject

The focal plane mark also serves as a reference point when measuring focus distance. Despite having the sensor being inside the camera body, this symbol allowed us to pinpoint the exact position of the focal plane inside the camera. Focal plane is the surface where the image is recorded. It is important to note that the focal plane will always remain in a fixed position regardless of the lens being used. And by knowing the exact focus distance of the subject to the sensor, photographers will be able to calculate the depth of field and use the optimum aperture value during a shoot with a reference to a focusing scale. 

3. Measuring Distance to a Subject

The focal plane symbol also serves as a point of consistency for measuring the subject distance to the camera. This distance information is often used as an anchor to ease the post-processing when you merge images or create composite images, as it ensures consistent image focus and proportions. This distance information will usually also be used in a set record to mark the position of the subject during an e-commerce product shoot to easily create repeatable results.

4. Lens Calibration

Apart from all the practical uses in photography, this focal plane mark is also used technically to calibrate photography camera lenses. It helps technicians to identify the position of the focal plane accurately to calibrate the lenses for optimal quality and sharpness in the lens focusing.

Conclusion

It’s worth noting that different camera models or lens systems may mark their focal plane symbol differently and in different positions as well. Therefore, it’s always recommended to look into the camera or lens manual for specific information on how the focal plane mark is marked in a particular system. This symbol, when put into use, can bring your image quality to a higher level.