User talk:Skinman
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A lens adapter is a device to mount lenses made for some type of camera on another camera for which they were not originally designed.
An adapter will receive any lens with a given type of lens mount, and attach it to a camera body with another lens mount.
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| lens adapters above: 1. M42 thread in Four-Thirds bayonet 2. M42 thread in Minolta SR bayonet 3. M42 thread in Minolta AF bayonet below: 1. M39 thread in M42 thread 2. Minolta SR bayonet in Four-Thirds bayonet 3. Exakta bayonet in Minolta SR bayonet image by Uwe Kulick (Image rights) |
A number of criteria need to be met by the camera, lens and adapter for the adapted lens to perform as designed. Otherwise, restrictions of functional limitations may apply and even damage may occur.
Contents
Flange focal distance
The flange focal distance (FFD) is a defining design parameter of the geometry of any given lens mount. It is the distance from the mounting flange (the metal ring on the camera and the rear of the lens) to the film or image sensor plane. It is always the same in any lens and camera with a certain type of lens mount, but the different types of lens mounts usually have different FFDs.
In order for the adapted lens to be able to focus to infinity, its FFD needs to be greater than that of the lens mount on the camera, giving room for the adaptor. Otherwise, the lens adapter needs to have integrated corrective optics for the lens to achieve infinity focus, like in the Canon FD lens to Canon EF camera adapter.
If the difference is small, other factors come into play, such as the diameters of the mounting flanges of the two systems. Lens adapters are generally easier to make when the camera body has a large lens mount.
Diaphragm activation
For improved ease of use, manufacturers began including a mechanical aperture linkage for automatic diaphragm control to more and more of the classical lens mounts since the 1950s. In such systems, which used to be the standard for decades, the diaphragm remains fully open until the shutter release is depressed, keeping the viewfinder image bright for easy image composition. When the shutter button is pressed, the diaphragm is stopped down via the mechanical linkage immediately before the shutter opens, and released again after the shutter has fully cycled.
From the late eighties, more and more modern camera systems with electronically controlled diaphragms were introduced. These no longer use a mechanical linkage between lens and camera but an electronic connection to transmit digital diaphragm control commands.
Adapters for two lens mounts with mechanical diaphragm activation may or may not have a coupling for it. Adapters meant to fit mechanical lenses to cameras with electronic lens mounts usually do not. In order to be able to stop down a lens with mechanical diaphragm control, most adapters without mechanical coupling constantly depress the diaphragm trigger once they are fitted to the lens. This means photographers need to stop down the lens manually with its f-stop ring before taking an image, and manually open the diaphragm each time they want a bright viewfinder image.
The cheapest and simplest adapters for electronically controlled lenses offer no way to stop down the lens. This is a severe functional limitation since hardly any lens achieves its full performance potential without stopping it down at least a little and because the diaphragm is lost as a means of depth-of-field control.
Slightly more advanced adapters for electronically controlled lenses have their own integrated diaphragm, mechanically controlled with a stop ring. These may or may not work well but will always impact image quality; at the very minimum, the bokeh is different for a different type of diaphragm introduced to the optical path in a different place than designed.
Adapters for autofocus lenses
The type of adapters mentioned above is common, to adapt lenses with manual focusing and manual aperture control; but adapters may be available for some modern lenses with electronic systems too.
The main efforts to support full automatic functionality of adapted autofocus lenses were made by the surviving big players in the camera market when they launched their CSC cameras. Most of them created own adapters including electronic translation units for the signals between camera and lens. These devices usually connect the lenses of an older SLR or DSLR system to the newer CSCs of the same camera maker. Thus the new camera types soon become popular among the brand's old fans since their old lenses work with full functionality on the hottest new digital system cameras.
Only a few independent efforts were made by accessory makers, some even to achieve inter-brand adaption of autofocus lenses. Metabones is one maker of such adapters. It offers adapters to mount Canon EF lenses to Sony E-mount, and others to attach them to Micro Four Thirds cameras, both adapters supporting electronic aperture control by means of the camera mount's original lens control signal protocol. The adapter variant for the E-mount even supports electrical focusing for many Canon lenses made since 2006, but according to Metabones`own product description that solution works slowly. To reach more buyers with that limited solution the adapters are also available as wide-angle converters with optics which boost an attached lens's speed significantly. Metabones calls these converter adapters "speed booster".
Products
- Metabones Speed Booster
- Metabones Smart Adapter
- Sony - 4 types of the adapter LA-EAn are available to attach old Minolta AF lenses or similar Sony lenses to CSCs with Sony E-mount like the Sony NEX
- Olympus MMF-1 adapter to attach Four-Thirds lenses to Micro Four-Thirds bayonets of Olympus` and Panasonic`s CSCs
- Canon Mount Adapter EF-EOS M to use Canon EF lenses on the Canon EOS M CSC bodies
- Nikon bayonet adapter FT1 for Nikkor lenses with F-mount on Nikon 1 system cameras
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