[Vintage lens] Flange focal distance and Macro photography

Flange focal distance (FFD/ flange distance)

For an interchangeable lens camera, the flange focal distance (FFD) (also known as the flange-to-film distance, flange focal depth, flange back distance (FBD), flange focal length (FFL), or register, depending on the usage and source) of a lens mount system is the distance from the mounting flange (the interlocking metal rings on the camera and the rear of the lens) to the film or image sensor plane.


FFD example for SLR and mirrorless cameras.


This value is different for different camera systems. The range of this distance, which will render an image clearly in focus within all focal lengths, is usually measured to a precision of hundredths of millimetres.

Lenses can be adapted from one mount (and respective FFD) to another. FFD determines whether infinity focus can be accomplished with a simple non-optical adapter. Optics to correct for distance introduce more cost and can lower image quality, so non-optical lens adapters are preferred.

A simple non-optical adapter holds the longer FFD lens the appropriate additional distance away from the sensor or film on the shorter FFD camera.

A camera body with a shorter FFD can accept a larger number of lenses (those with a longer FFD) by using a simple adapter.

A lens with a longer FFD can be more readily adapted to a larger number of camera bodies (those with a shorter FFD). If the difference is small, other factors such as the sizes and positions of the mounting flanges will influence whether a lens can be adapted without optics. Such as medium format lenses, they usually have longer FFD to avoid the large reflex structure.

The FFD of SL42/EF mount is 44 mm which might be one of the shortest FFD for full frame SLR cameras/lenses. Shorter FFD brings the compatibility to use other lenses with longer FFD.


Part of the FFD table from Wiki for reference.


Theoretically SL42 is compatible for lenses with FFD no shorter than EF mount by using none optical adapters. But there are still some limits for the mount coupling.

EF-S lens has a longer bottom behind the last elements which is customized for APS-C lenses and cannot be mounted on full frame cameras because of the mechanical limit. But EF lens could mount on EF-S cameras reversely.

Mount diameter may limit the size of the adapter when using lenses with similar FFD. The adapter may also trim the image field of the lenses with larger format, such as mounting medium format lens on full frame cameras.

For the vintage lenses with mechanical aperture pin/indicator, they may interfere with camera internal structure.


Retrofocus lens

The optical system of lenses usually has symmetric character of field of view (FOV) and back focal length (BFL) when the total elements are less than 8. It means that the Effective focal length (EFFL/EFL) of the lenses is proportional to BFL which is partial related to the FFD.

Especially for vintage lenses without multiple coating technology in old days, more elements mean more reflective and lower light transmittance. It is hard to design wide-angle lenses (shorter BFL) with longer FFD (need longer BFL to hold the reflex structure).

The Angénieux retrofocus for still cameras was introduced in France in 1950 by Pierre Angénieux. The Angénieux retrofocus photographic lens is a wide-angle lens design that uses an inverted telephoto configuration. The popularity of this lens design made the name retrofocus synonymous with this type of lens.

Generally, we could also call the wide-angle lens as Angénieux type, retrofocus or inverted telephoto.


Optical design of the first Angénieux lens


Construction: 6 elements in 5 groups

Max aperture: f/2.5


Pierre Angénieux applied for a patent in 1950. In the original patent, he presented two lenses with an angle of view of 65°, approximately equal to the view of a f=35mm lens on the 35mm format for still cameras; the first example had a maximum aperture of f/2.5, while the second example had a maximum aperture of f/2.2.

At approximately the same time, Harry Zöllner and Rudolf Solisch applied for a similar patent on an inverted telephoto lens design, branded Flektogon, for Carl Zeiss Jena. Carl Zeiss Oberkochen also created an inverted telephoto design branded Distagon (5.6/60mm) for the Hasselblad 1000F in 1952.


NONS SL42 + Flektogon 40/4 (photo by: utut_photo)


Made in focal lengths of 24 mm, 28 mm, and 35 mm, the Angénieux retrofocus lens inspired other lens makers to produce wide-angle lenses of this type for almost every 35mm SLR, and helped to make it the definitive camera type of the late 20th century.

But for mirrorless systems, it shall be easier to design the wide-angle lenses because of shorter BFL and FFD.


Macro photography

Macro photography (or photomacrography or macrography, and sometimes macrophotography) is extreme close-up photography, usually of very small subjects and living organisms like insects, in which the size of the subject in the photograph is greater than life size (though macrophotography also refers to the art of making very large photographs).

By the original definition, a macro photograph is one in which the size of the subject on the negative or image sensor is life size or greater. In some senses, however, it refers to a finished photograph of a subject that is greater than life size.

There are several ways to achieve macro photography such as macro lens (e.g. Canon 100mm macro), close-up lens, reversed lens (including reversed lens coupling telephoto lens, e.g., Nikon EL series), extension tubes and bellows etc.

Optical scheme of macro photography using extension tube


Keep in mind the symmetric character of the lens optical system, it is not only related to the BFL and EFFL but also the entrance pupil and exit pupil which are useful to get proper magnification.

Bellows works similar as extension tube and will give a more secure setup and more flexibility than a set of extension tubes.


  • Inexpensive

  • No lenses inside

  • Easy to use


  • Limited length

  • Will lose working distance

When shooting with SL42 + bellows, please note the ambient light meter will be inaccurate for aperture reference. And extra lighting is usually needed because of the short working distance.