Understanding Focal Flange Distance for Vintage lens photography
I am trying a new ritual started by the Clear Writing community of Amit Varma. We write at least 200 words every day of November and see where it goes. The pictures are my street photography shots.
This is a bit off-topic. We are talking about photography. A specific kind of photography that uses old manual lenses from Film era. These lenses can be interchangeable and interoperable. It gets interesting when you can adapt vintage lenses (made in the 50-the 60s) to modern mirrorless/DSLR. You can get that cozy feel from the images. It can save you money and provide an opportunity to develop skills as an amateur photographer. Vintage lenses, in most cases, will only work in manual mode, with little focus assistance (some cameras have focus peaking to assist). This makes you take your time in composing the shot, appreciating the scene, or if it even has to be clicked. This added effort helps develop observations skills too.
FFD is an important concept to understand interoperability between lens systems. FFD is the distance between the mounting of the lens and the surface it forms an image. I understand it as, the distance at which a camera expects the lens to produce an image. In older cameras, this is where the film would be. In modern cameras, it is the image sensor. There is often a 'circle with a line through it' mark that indicates the lens plane. The distance between that mark and the bayonet is the FFD.
The FFD varies with the mount type for your particular camera. For example, my Nikon camera with a Nikon F-mount has an FFD of 46.5mm. This means the ring where I mount my lens is 46.5mm from the sensor.
Now, I recently purchased a cheap wide-angle 16mm C-mount lens. These lenses are used in CCTV cameras. The FFD for this lens is 17.526mm. This means the lens makes a sharp focussed image at 17.526mm.
What if I want to mount it on my Nikon? Is it possible, optically for the lens to function?
The answer is No! Since the camera (Nikon) has an FFD (46.5mm) greater than the adapted lens (17.526mm). We cannot just place the lens (17.526-46.5) -28.974mm away from the flange to get a well-focussed image. Hence, a C-mount to Nikon F-mount adapter does not exist. But the reverse exists.
So, if like me you want to play with Vintage lenses, try and get your hands on a camera with a low FFD like Fujifilm X, Canon EF-M, Sony E-mount, or even a Micro four-thirds.
A good thumb rule is that you can only buy lenses from a system with an FFD higher than yours. So, if you own DSLRs, it is unlikely to find good lenses to adapt.
I should probably make a small calculator for this.