The Forgotten Symbol on Your Camera

Jan 21, 2024

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.

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.

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.

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.

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.

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.

Focal plane mark on Canon 5DSR

Focal plane mark on Sony A7R2

Focal plane mark found in different cameras

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.

Yang Zhen Siang is a commercial photographer specialising in architecture, food and product photography. He help businesses to present themselves through the art of photography, crafting visually appealing and outstanding images that sells.

Short and sweet! Thanks for the info. I did not realize the minimum focus distance is measured from this point.

Welcome and thanks for reading.

I used to shoot 16mm film from 1971 to 1985 using an Auricon and a Bolex. This was where you measured from the camera to the subject. I feel old, but then again, I am old.

Its crazy how much convenience that technology has brought us. Makes the process of photographing totally unrecognizable from where it began. Glad to know it was heavily in used back in the days

I forgot about this after I stopped using my first removable lens camera, which was a film camera. It's funny what one's brain can ignore right in front of our own eyes. Thank you for the article!

thank you for reading! glad that I am able to bring more awareness into the younger generations and refresh the memories of certain aspects in photography.

Remembering the days of film when you were getting your school picture taken and the photographer had a string or such and had your nose at the right distance, a long time ago!!! I believe also for the lighting always the old (but still used) hand held light meter. AF today is so wonderful and focus peaking with in camera color to see what is in focus. Also long ago the red or green and white colored numbers on the old film lenses. All to bend the photographers mind where unknown to all not into photography your Math Skills are a must and solutions prefect and you had to wait a week or month to know if you were right. The next thing was your log book (remember) of solutions you keeped for each image number on each roll of film, even today as many are returning to film are they unaware the value of the record book of image math ah! yes the slide rule the mystical 3 pieces of wood with markings that helped solve math problems back in the early 70's that got me through advanced Nuclear Electronics school in the Navy, there are so many things photography skills translate into life getting up further some steps. Ever walk into a military recruiting station and whip out that yellow stick with marks they put you in a different room!!! It was the tube days and the first hard drive a disk in a big metal cylinder charged with nitrogen and programed with punch tape. No one ever things of the math until they get off of auto mode!Yes the two cameras had built in light meters the first with math solving circuits even etched glass in viewfinder for focusing, so spoiled!

Thanks for sharing your part of the story. Yes its insane how much technology has bring convenience to us..which to me is both good and bad.. most photos taken today no longer have that thoughts behind it of why such decision was made, why it was composed this way etc etc.. imho, it had taken a way so much fun in photography away

Doesn't the focal plane change with different lens mounts? If so isn't this problematic when using lenes not fitted for a particular mount?

It's not a problem if you use a correct adapter with the exact spacing needed to place the lens the proper distance in front of the focal plane. If you've got a lens made for 44mm registration distance and you want to use it on a camera with 20mn registration distance, you need an adapter that is exactly 24mm thick. Thus the flange of the lens is placed 44mm in front of the focal plane by placing the flange of the lens 24mm in front of the camera's flange receiver.

Agree with Michael.. The focal plane mark will act as the constant when adapting different lenses to your camera.

Nope, I haven't forgotten what this symbol means since I first learned it over 40 years ago.

Glad it is still being remembered.. 50 years down the road i doubt people will still remember them judging by how things are now made easy with technology

I literally saw this today and was wondering. This is perfect!

thanks for reading! what a timing