What is Flange Distance on a Camera?
Flange distance is the distance between the lens mount and sensor of a camera. It varies between manufacturers and types of cameras. This is why you can’t always interchange lenses between brands and types of cameras.
The most important factor in determining flange distance is whether the camera has a mirror. A mirror mechanism will increase the minimum required flange distance of the camera system.
So if one placed the lens mount too far back, the mirror would hit it every time it flips.
Typically, SLR and DSLR systems that have a mirror have flange distances of around 45 mm. Those that don’t have a mirror will have flange distances under 20mm.
Focus and Flange Distance
Most lenses focus by moving their rear element. When they want to achieve a close focus, the rear element moves further from the sensor. When they are focusing to infinity, the element is closer to the sensor.
If the lens can’t get close enough to the sensor, it won’t be able to focus to infinity. This makes it inconvenient for all lenses except a macro lens.
This phenomenon determines what lenses can be adapted to different camera mounts.
Flange distance plays a key role in defining if a certain lens can be adapted to a certain camera body. Basically, the lens can be adapted to the camera if its intended flange distance is longer than the camera body’s flange distance.
However, there are exceptions. For instance, lens adapters are exactly as thick as the difference between the flange’s distance of the camera and the lens. Therefore, the difference must be significant enough to let an adapter fit.
You must also be careful if you plan to adapt vintage lenses with parts that extend rearwards. In these cases, you may have to physically modify the lens, so it fits the adapter.
If you want to adapt lenses that wouldn’t otherwise fit because of their shorter flange distance, you can also use their lens element to shift the focus of the lens, so they push the infinity focus farther away from the sensor.
However, these adapters may affect optical quality reducing color accuracy and focus and causing distortion.
The Mirrorless Mount Advantage
Mirrorless mounts have an advantage when it comes to adaption because their flange distance is shorter than that of other types of models. Therefore, they can adapt to any type of lens.
Now that you understand what flange distance is on a camera, you can better understand the different lenses you can use on different camera systems. And if you can’t buy them, you may be able to make them yourself. Which path will you choose?