The adapter seen here is an M42 (x1.0) to Canon EF adapter. It allows an M42 mount lens to be used on a Canon body. This is one of the most commonly used, simplest and least expensive adapters.		This Mirex Tilt/Shift adapter is an example of a very complex and expensive adapter. This adapter allows various medium format lenses to be used on DSLR's with both Tilt and Shift functionality.

Other camera and lens combinations need to use the specific adapter for that combination. But, not all cameras and lenses can be used interchangeably so it's important to understand the circumstances which enable certain combinations to be used.

Stop Down Metering, the biggest disadvantages of using adapted lenses

In almost all cases the lens will not be able to communicate with the camera so the lens will simply be physically attached to the camera and that's all. If you rotate the aperture ring on the lens then the aperture will actually open or close but the exact position of the aperture will not be known to the camera and can not be recorded in the EXIF.

One of the consequences of this lack of connection between the camera and lens is that exposure metering will need to take place at the working aperture and this is called 'stop down metering'. For example, if you want to shoot at F8 you will have to have the lenses aperture set to F8 when you take the picture but this will could make the image too dark to focus and compose or the depth of field may simply be too wide to focus accurately. Ideally the lens would be opened up fully to provide a bright image and make focusing easier and then stopped down to F8 just before the picture is taken. OEM lenses do this automatically but adapted lenses (with a few exceptions) do not have the mechanical or electronic linkages to the camera to allow this to happen. Adapted lenses are easiest to use when they are used wide open, or close to it, where they can be left at the working aperture to meter and shoot. Stop down metering is fine for subjects where there is the time to work slowly and carefully, such as landscapes, still life, macro etc.

Many cameras can be left in an 'aperture priority' metering mode where they will set the shutter speed based on the light passing through the lens but some cameras might need an exposure compensation factor dialed in depending on the lens and aperture being used (trial and error will quickly tell you if it's needed).

How do you focus Alt lenses?

Some adapters have electronic chips, often called 'chipped adapters', which communicate with the camera and these allow the cameras auto focus to indicate when manual focus is accurately achieved with the lens. This does NOT mean that the manual lens becomes an auto focus lens, only the cameras AF indicator in the viewfinder will light to indicate focus. Using the auto focus assist on a cameras body won't always give you a better focused image as the cameras AF may not be very accurate in the first place or you might be limited to using the cameras AF points to focus but if you are uncomfortable with focusing manually then these chipped adapters can be quite useful. Some of these adapters can also be programmed for the focal length to be included in the EXIF. Certain cameras may even require a chipped adapter to allow the camera to operate at all.

Many types of adapters are available however simple non-chipped adapters are the least expensive and simplest to use as long as you are comfortable focusing manually.

Focusing manually will always be the most accurate way to focus but it is not always easy and may even take a lot of practice to become proficient. Unfortunately most modern cameras are intended to be used as Auto Focus cameras so their focusing screens are not always well suited for anything else. Many cameras have focusing screens which give a bright image which is easy to see and compose but this actually makes the screen poor for focusing. Many cameras also have very small prisms and viewfinder magnification so the image you see is often smaller and darker than it could be. Some cameras allow the focusing screen to be replaced and this is often worth doing if you plan to use Alt lenses regularly.

The importance of accurate focusing can not be emphasised enough. You might find that your existing lenses perform better than you think, if only you focused them accurately and used a tripod, mirror lockup etc. All lenses will only deliver a sharp image at the exact point where they are focused and sharpness will fall off slowly in front and behind that point.

Although not practical for fast moving subjects, using Live View (or equivalent) and zooming into the subject allows the maximum focusing accuracy, even in dark environments where focusing would be almost impossible.		Accurate focusing is critical to getting the most from a lens, especially where narrow depth of field is employed.

The best and most accurate method to focus any lens, alternative or otherwise, is to use Live View (or equivalent) as this will allow you to zoom in on the subject and focus exactly where you want to. Unfortunately this method is not very practical and is also slow to use, but so are Alt lenses, so this makes Live View and Alt lenses a match made in heaven!

Proprietary lens mounts and register

Almost all 35mm or medium format cameras with interchangeable lenses use a custom or proprietary lens mount. This means that the connection between the camera and lens is unique to that specific brand of camera and that lenses from another brand of camera can not be attached to it. These custom lens mounts are often of the same basic design, often with a 3 or 4 prong bayonet for example, but the linkages and electrical contacts that the lens needs, as well as various important physical dimensions, are all quite different. So a Nikon lens will not work on a Canon body, a Pentax lens will not work on a Minolta body etc, etc. There certainly are some exceptions, such as Yashica ML and Contax Zeiss (SLR) lenses which are interchangeable on Yashica and Contax SLR cameras. There are also a large range of 'M42' mount lenses which are interchangeable over a number of cameras. There are other mounts which are interchangeable but these are less common and usually belong to even older cameras, such as Contax, Nikon and Leica rangefinder cameras.

The 'register' of the lens mount is one of the determining factors regarding which cameras and lenses can be used together but there are other factors relating to specific lenses, such as protruding rear elements that simply won't fit inside certain cameras, or even camera bodies which might have larger mirrors and there fore less clearance for certain lenses to actually fit. Some times things just don't physically fit!

The 'register' is the distance from the surface of the lens mount on the camera to the film or sensor focal plane itself and is the same set distance for any specific camera system or mount, such as Canon EF or Nikon F. The register is very important in determining if a lens can be readily adapted to another camera because this will determine if there is enough room for an adapter to fit between the camera and lens and still keep the lens the correct distance from the film/sensor plane. If there is no room for an adapter then any adapter that is used will act like a macro tube and prevent infinity focus. Certain lens/camera combinations are effectively ruled out because of differences in lens register, such as Minolta lenses and Canon bodies. Using a Minolta lens on a Canon body requires the Minolta lens mount to be drastically altered (shortened) to resolve the difference in register. This operation (commonly referred to as 'surgery') is not for the feint hearted and is often irreversible.

Some cameras have longer registers, such as Nikon F mount, whilst some have shorter registers, such as the Canon EF mount. This predisposes some camera systems to being used with alternative lenses because there is simply more room for the adapter and clearance to the rear of the lens being used. Mirrorless cameras have a very short register so are ideal for use with alt lenses.

Another factor is the potential for mirror 'collisions' between the rear element of a lens and the mirror in a DSLR. Note that a crop camera like a Canon 10-70D will have a smaller mirror than a full frame camera like a 5D, 5D2, 6D, 1ds2/3. This is an important distinction so a lens might work on a certain Canon crop camera, for example, but foul the mirror on a full frame camera of the same brand, or even a full frame camera of the same brand but a different model (5D vs 5D2). It's important to research each specific lens and camera body combination before trying to use them otherwise damage may result to either the camera, lens or both. Cameras with electronic view finders such as mirrorless and M4/3 do not have this issue, because they don't have a mirror, and are the easiest to adapt to alternative lenses.

Other Alternative lenses

Almost any lens can be mounted to a digital camera. Some commonly used lenses are enlarging, large format, cine, TV, video and projection lenses. All of them have certain specific applications where they perform best and others where they may perform poorly but can be fun to use and can some times offer interesting creative effects.

Enlarging lenses are a group of lenses which are often overlooked for use on modern digital cameras however many of them are ideally suited to certain types of photography, some times more so than the lenses offered by the camera manufacturer itself. They span the focal lengths from around 28mm to in excess of 300mm with the most common focal lengths being 50mm-75mm which are typically the least expensive too. Wide angle to moderate lenses, 28mm-50mm, allow large image magnification when mounted on a bellows so are well suited to macro work. Longer lenses in the 75-135mm range are more useful for photographing products at close to moderate distances.

Enlarging lenses are excellent for product, close up or macro work and can often be used on a swing/shift bellows to offer technical controls such as swing (left/right) or tilt (up/down) and shift which is impossible with non tilt/shift lenses.

Tominon 135/4.5 lens, mounted to a Nikon PB-4 Swing/Shift Bellows, mounted to a Canon 5D2 body. This configuration of equipment is quite useful for Macro or product photography although it can also be used for normal scenic photography as long as infinity focus can be achieved. The Swing action is shown above. The term Swing refers to  horizontal (left/right) pivoting whilst Tilt refers to vertical (up/down) pivoting lens movements.		The Nikon PB-4's Shift functionality is shown above. Swing and Shift can be used simultaneously if required, as is often the case. The Swing and Shift functionality of the bellows offers some, if not all, of the functionality of far more expensive and cumbersome view or technical cameras.

Enlarging lenses can also be used for normal photographic purposes, such as portraits or landscapes, not just macro or product shots. However it can be difficult to use lenses shorter than 75mm on Canon/Nikon or similar DSLR's for normal photographic purposes and still achieve infinity focus, although this depends on the cameras register and the focusing mechanism (or helicoid) that is used. The cameras register is the limiting factor so cameras with shorter registers, such as Sony NEX and similar, allow shorter focal length lenses to be used and still achieve infinity focus.

Although many enlarging lenses have a 'normal' or 'standard' M39x1.0 thread they also very often have unusual or unique threads such as M39x0.75, M40x0.75, 1.5"x24tpi all of which look like an M39 thread until you try to actually attach them! Enlarging lenses really do have a very large range of thread sizes, especially many of the American enlarging lenses such as Elgeet, Kodak and Wollensak, but fortunately most enlarging lenses have very simple threads so even if a custom adapter needed to be made it would be simple to do, but not always cheap.

Large format format lenses can also be used and are similar to enlarging lenses in their use and application but many large format lenses don't quite have the very high resolution of enlarging lenses. Instead they offer very large image circles which makes them ideal for tilt/shift applications. Large format lenses have a relatively narrow range of thread sizes or mounts as they are generally designed to fit into standard shutters such as Copal 0, 1 and 3, but there are always exceptions. This makes it easy to use them in one respect but the problem is attaching the lens to the camera as there are no adapters specifically designed to do this. The easiest and most common method to adapt a large format lens to a DSLR is to use a View camera with a DSLR adapted to the rear standard of the camera. This technique gives full technical or view camera controls and is excellent for product shots or close up work. The main disadvantage is that it is almost impossible to achieve infinity focus with focal lengths shorter than approximately 80mm. Other disadvantages are weight and ease of use. View cameras are no longer very expensive so cost is not a major factor as it might have been many years ago.

This is a Helicoid and is shown fully contracted and extended. A Helicoid has a ring or collar which you can turn to adjust it's length so it is a mechanism for focusing lenses. This one has M42x1.0 threads on both front and rear so can easily be adapted to most cameras with the appropriate adapters.		This Meopta Meogon 80/2.8 Enlarging lens is being used with a Helicoid to provide focusing ability. It attaches to a Canon Body and achieves infinity focus. Note the various components needed to attach the lens to a camera, from left to right, M42 to Canon adapter, M42 Helicoid, M42 to M39 adapter, then the Meogon lens itself (which has an M39 thread).

Many lenses such as enlarging, large format and projection lenses do not have any focusing mechanism, or helicoid, built into them so you must provide one if you wish to focus them. There are several ways to do this but the method you choose will depend on the lens used. One way is to use a commercially available helicoid where the lens attaches to the front of the helicoid and the camera attaches to the rear. The helicoid has a ring, like a focusing ring on a normal lens, which when rotated will alter the length of the helicoid, thereby allowing the lens to be focused. Helicoids are available in several lengths and the helicoid needs to be the correct length for the specific lens used otherwise it won't be possible to achieve infinity focus. Helicoids are most commonly available in an M42x1.0 mount (front and rear).

Another way to focus enlarging lenses is to use a bellows with the appropriate camera mount at the rear and possibly an M42x1.0 thread at the front which can then have the appropriate adapter fitted for the enlarging lens. This method is very easy to use and is generally well suited to lenses longer than approx 80mm if infinity focus is needed.

This Mamiya M645 medium format Macro lens is being used with the Mirex adapter in place of the Canon Macro lens because the Mirex adapter allows both Tilt and Shift adjustments which are not possible with the standard Canon macro lens.		The Mirex adapter is shown here with 10 degrees of Tilt applied to the lens. Using Tilt allows careful control of the focal plane which is particularly useful when photographing products and even for general purpose photography.

Many medium format lenses can also be adapted and offer certain advantages over typical 35mm lenses because their register is so large that special adapters with tilt and/or shift can be used to allow much greater flexibility and technical control than normal non tilt/shift lenses.

Where to buy adapters?

Adapters are available from various online sellers, primarily through the popular auction sites such as Ebay, however many of the better quality or specialised adapters are only available directly from the manufacturers themselves.

In some cases it is not possible to buy an adapter so one might have to be custom made. This is an expensive option but some times it's the only way. Custom adapters might be as simple as a ring with different internal and external threads or possibly even a complex adapter with bayonet fittings on either side. If an adapter does not already exist for a camera/lens then it is either technically impossible (such as Pantax 645 to Mamiya M645) or there is simply too little demand, such as some of the exotic enlarging lenses which have a wide range of thread dimensions.

Some adapters can even be home made and very cheap.

"What could happen?", or, "If it sounds too good to be true..."

Although there are many advantages to using Alternative, Legacy or Vintage lenses there are also potential problems with using lenses that are simply, well, old. A lot can happen in 20, 30, even 50 or more years. Some lenses are very simple and easy to repair or maintain whilst some are very complex and require special equipment, parts and knowledge. If you have a problem with the later type of lens then chances are you might not be able to have it repaired at all. Most lenses are simple enough to be repairable by experienced camera technicians, depending on the fault of course.

There are many different things that can go wrong with a lens, depending on the specific lens in question, so it's difficult to give a comprehensive list of things to check.  Some of the most common faults or problems are listed below.

Certain models of lenses can be prone to certain faults but it's often easy to find these things out by doing a little research before buying the lens.

Many old lenses can be very cheap...		...this is some times the reason, fungus or mould. Many sellers do not disclose the existence of fungus, some times because it significantly devalues a lens, other times because they don't even know what it looks like.

Many lenses are sold by inexperienced sellers who may not even recognise the existence of faults, such as fungus, in the lenses they are selling. If buying second hand lenses then it is advisable to do so from reliable sources and preferably with the option to return the item if unsatisfied.

Resources

There are many online resources and forums dedicated to using alternative lenses. Some are listed below and the links will open in a new window. Online forums are ideal places to ask specific questions about camera/lens combinations as it's likely that many people have already tried it and are usually willing to share their experiences and knowledge.

Fred Miranda Alternative Lens Forum; http://www.fredmiranda.com/forum/board/55

GetDPI.com, The Alternative Forum; http://forum.getdpi.com/forum/alternative-forum/

Macro/micro photography Forum; http://www.photomacrography.net/forum/