Before I go any further, anyone looking for information on point and shoot (P/S) cameras in this post may stop reading now as P/S cameras have one lens built into the camera and it cannot be changed (at least not at a cost and effort worth entertaining). I promise in a future post to write a topic specifically about P/S cameras and how to select one, including what to look for in the lens, but for this week, interchangeable lenses and there mounts are the topics and are only relevant for DSLR users, and other interested readers.
In my very long and hopefully helpful first post, I included one aspect to take into consideration when selecting a DSLR are the lenses that can possibly be mounted on the camera body. Also, I may have lied about it being my longest post because this one is in fact longer, but I have broken it out into brands, so if you are looking for info on one particular brand's mounting system, feel free to skim to that section, but also realize there are some considerations that apply to all lenses. In the first post, I described that both Canon and Nikon make great lenses (in general), and they only produce lenses for their respective camera systems. What do I mean they only work on their respective cameras? A lens is just a tube with glass in it that focuses light, right? And light is available everywhere, so it’s not like a Nikon will only use Nikon light, and Canon only uses Canon light. Well, I may have over simplified this argument, because it probably makes sense that what I meant is that, natively, a Nikon lens will not mount on a Canon body and a Canon lens won’t mount to a Nikon body, and they do not produce lenses with mounts for any other camera systems. And this is not restricted just to Canon and Nikon, but I chose them because they are the two biggest players in DSLRs today. The fact of the matter is, most camera makers who also make lenses, only make lenses that work on their cameras, with only a handful of exceptions (Sigma being one of those).
Now that this is clarified, what do I mean by a mount? In the simplest of explanations, a lens mount is a bracket or flange on the end of the lens that allows it to attach to the opening on the front of the camera body. The flange, or mount, fits and secures to the corresponding bracket surrounding the opening, securing the lens in the proper place for it to focus light on the film plane or image sensor. Each camera system manufacturer has a different way of accomplishing this. There are also 3rd party manufacturers who produce lenses with a variety of mounts for use on different camera systems. I’ll touch on some of the major ones, new and old, and how they attach.
There are essential three types of lens mounts: screw mounts, breech-lock mounts and bayonet mounts. Screw, or thread mounts, while occasionally still in use today, were effectively replaced by bayonet mounts. They are less secure and more finicky than bayonet mounts. They are essentially a threaded end on the lens that screws in to a corresponding threaded end on the camera, much like a bolt (the lens) screwing into the correct size nut (the camera body). The screw mount required multiple turns of the lens to attach and detach from the camera, and did not accommodate the use of electronic communication between the lens and body, although mechanical linkages were possible. On the flip side it was also cheaper and more universal than the proprietary bayonet mounts or breech-lock mounts that were developed. In general, screw mounts fell out of use in the late 1970s, in favor of the more user friendly bayonet mount.
Before moving on to the bayonet, there were also quite a few breech-lock mounts that were developed. Breech-lock mounts, or friction mounts, worked by placing the lens against the opening on the camera body and rotating a ring that caused the mount to “grab” the corresponding bracket on the camera and secure the lens. The benefit of this type of mount was that it did not require the sliding of the surface on the lens against that on the body, which potentially after a long period of time could result in a change in the delicate tolerance affecting the distance of the lens from the film, or image sensor. Ultimately these fell out of favor with some of the big camera manufacturers due to the easier and more secure bayonet mount, which also more easily accommodated electrical connections, but you will still find them today on some brands and for use on cinematic movie cameras.
The bayonet mount, is not new, but it is by far the most popular today. In fact Nikon’s bayonet mount (also known as the Nikon F mount) came out in 1959 and is still in use today, although with some additional features and electrical connections have been added. A bayonet mount is essentially two interlocking brackets, one on the lens and one on the camera body. Most major camera manufacturers use their own proprietary bayonet mount, although some do share common mounts. For examples, the Nikon F mount is used on some Fujifilm, Kenko and Sinar cameras in addition to all Nikon SLR and DSLRs. The bayonet is great because it allows the lens to be attached and detached easily, quickly, and precisely time after time. It helped to eliminate many of the downfalls of the screw mount while mounting a lens with less time, requiring less than a quarter turn.
So what mounts are out there, and which one should you pick? Well I’ll answer the second question first. Do not under any circumstances select a camera based on the type of mount it uses. All modern bayonet mounts work fine and you should focus on the other camera and lens features, and let the lens mount be a byproduct of the camera system you choose. Now on to a selection of common, and previously common lens mount types organized by the camera system they were used on. I’ll also add some notes about them if I have any. Please note that this is not an exhaustive list, and there are also some camera systems that use common mounts. I’ll highlight some of those as we go along.
Nikon – Since I am a Nikon guy, I decided to start here. As mentioned above, Nikon developed the Nikon F mount bayonet and its first commercial release occurred back in 1959. Like many other bayonets, it makes use of three flanges on the lens to secure the lens to the body with a simple twist. Nikon’s lens mount is notably one of the smaller ones in the industry. The hole, or throat, on the camera is only 44mm wide. While there are smaller, there are definitely more that have larger throat diameter, which means many other lens mounts cannot be adapted to fit on Nikon bodies, but Nikon lens can be used on other cameras. The registration distance, or distance from the rear element on the lens when mounted to the plane on the image sensor is also longer than most, at 46.5mm. When adapting lenses to any other manufacturer’s body, there are considerations you need to take into account, and this is one of the big ones for using a Nikon body.
As I mentioned above, Nikon’s mount has remained relatively unchanged since 1959, which means for the most part, you have great backwards compatibility of lenses. The only really prohibitive change came in 1979 when Nikon introduced automatic indexing, AI for short which requires a recess in part of the lens to accommodate the AI tab on the body. If using a body that can perform mechanical AI, using a pre-1979 can damage the camera without modifying the lens. More on this in a future post, because it is relatively easy to do. A quick note, Nikon also produces DX lenses where the lens design is meant to work on cameras with the smaller DX (APS-C) sensor size by producing a smaller light cone and image circle. Although these would produce significant vignetting on a full-frame DSLR, the actual mount is identical. As such Nikon has designed their full-frame cameras to have a crop sensor mode which only uses the center of the image sensor if it detects a DX lens has been installed. The best bet though is to check the manual or manufacturer website for compatibility before throwing any lens, new or old, on your camera body.
Canon – Another of the major players in the camera market, Canon has taken a different approach to Nikon and made several changes to their lens mount over the years, finally arriving at the EOS EF and EF-S mounts. Originally, but briefly, Canon SLRs used an M39 screw mount (see below for more on M39 and M42 mounts). They quickly transitioned to to 2 different varieties of a breech-lock mount, the FL and FD mount, in that order chronologically. Lastly, with the advent of the EOS line of cameras in the late 1980s, the EF mount was introduced, and more recently with digital EOS, the EF-S. As M39 mounts were used on other camera brands, Canon decided to move to a proprietary breech-lock to prevent other lenses with potentially different registration distances from being mounted on the camera and vice versa. The different iterations of the breech-lock were developed a few decades until finally the EOS line was launched.
The biggest difference between the FD and EF mount aside from the physical connection, as that Canon changed the registration distance moving from 42.00 mm to 44.00mm. This change meant that you could not easily adapt an old FD lens to an EF mount body. For a period of time Canon sold an adapter with special correcting glass to help ease the transition, but the adapter was a couple hundred dollars, and photographers eventually just sold their old body and lenses to fund a new EOS body with EF lenses. EF lenses are still sued today, however there is another consideration to take into account. The EF-S lens specification was put in place. EF-S (the “S” stands for short back focus) was designed for use in cameras with the smaller APS-C sized sensors. It physically reduced the size of the light cone projected on the sensor similar to the DX designation for Nikon. However, unlike Nikon DX lenses (more on this in a later post), EF-S lenses mount the back element closer to the image sensor, although the flange to sensor distance is still 44.00mm. So what does this mean? It means that cameras had to be designed with more clearance to prevent the mirror from hitting the lens when the shutter was actuated. It also meant that EF lenses could still be used on EF-S compatible bodies, but not the other way around. So if you have an older EF body, you could not put an EF-S lens on the body as to potentially risk damaging your camera mirror. Canon, in an attempt to prevent this from occurring changed the alignment marking on the camera and lens to alert the user that the lens may not be compatible. This is less of an issue with new cameras using the APS-C sensor size as they have designed all of the crop sensor cameras today to be able to take EF-S lens. Canon cameras with full-size sensors will not accept EF-S lens, however because of the reduced light cone, and resulting image circle projected on the sensor, users of full-frame bodies would see significant vignetting in their photos, so the incompatibility is not a great loss.
Pentax – Another big player in the SLR market, less so now in the digital age is Pentax. Pentax used a couple of different mounts, first the M42 screw mount, and finally the Pentax K bayonet mount. I will focus on the M42 mount below as it was used by many different manufacturers. In the US this unofficially became known as the Pentax universal screw mount even though outside of the US it was known as the Praktica universal screw mount even though both are technically M42 universal screw mounts, but I digress. The Pentax K mount is a bayonet mount that preserved the registration distance from the M42 mount. Although M42 and K mounts are directly incompatible, it allowed Pentax to preserve much of their engineering work during the transition by simply swapping out the mounting brackets rather than redesigning lenses optically.
Olympus – Camera maker Olympus, came out with their first SLR in 1971, which was 12 years after Nikon and Canon. Their first lenses used the OM bayonet mount, and they continued with that mount until 2002, when they, along with Kodak, developed the Four Thirds system of sensors and lenses. The OM mount was designed for a 46mm registration distance, and similar to Nikon had a relatively narrow throat. Also a fact that made it very adaptable to many other camera systems with simple mechanical adapters. Because Olympus was a founding company of the Four Thirds system, and Kodak really does not produce any DSLRs, I will focus on that system here. In short the specification for Four Thirds system was designed to make the most recent attempt at creating a normalized system of standards for DSLR. Several companies have since joined on to the specification including Fuji, Leica, Panasonic, Sanyo and Sigma, although up to this point only Olympus, Leica and Panasonic have compatible bodies. The Four Thirds sensor size is much smaller than even the standard APS-C crop sensors (1.5x and 1.6x from Nikon and Canon, respectively). It also uses a 4:3 aspect ratio where typical sensors and 35mm film use a 3:2 aspect ratio. Although different, this does not make it worse. In fact, it has many advantages with one of the obvious ones being the interchangeability of lenses between different brands. Although meant to begin standardizing the industry, many camera makers, including most of the major manufacturers still prefer to make their own proprietary lenses and sensors. As such, you may see in the future that this gets renamed to something proprietary to Olympus and Kodak.
Sony – DSLRs were not really a consideration for Sony until Minolta was nearing the end of its business in 2006. At that point Sony jumped in and bought up all of their assets and technologies, including the Minolta AF mount, or simply the Alpha mount. At this point the Sony Alpha line of DSLRs was born, using the alpha mount. It functions similarly to all other modern bayonet mounts.
M42 and M39 Universal Mounts – Although M42 and M39 mounts are different and were used by different companies, I grouped them together because they shared similar properties. The M## designation reflected the metric 42 or 39mm screw thread. Both used a thread pitch of 1mm. T-Mounts (see below) also havea 42mm diameter, however it uses a 0.75mm thread pitch and is not compatible with M42 cameras and vice versa. The M42 mount was first developed by Carl Zeiss back in the 1930s, and was adopted by many European, and particularly Russian camera and lens manufacturers. The M42 standard utilized a 45.46mm registration distance. As I mentioned above in the Pentax section, the Pentax camera company utilized the M42 mount as well. In the United States became known as the Pentax Universal Screw mount. The same occurred with the Praktica camera brand outside the US, however both are M42 universal screw mounts. The M39 screw mount was developed by Leica prior to the development of the Leica R bayonet mount and had a registration of only 28.8mm which is too short for many other cameras. Early Canon cameras used it (but called the J-mount) as did several of the Russian camera brands. The Zenit camera brand adopted the M39 configuration but extended the registration to 45.2mm. There is no visual difference between the mounts with different registration distances, so you must know which one your particular M39 lens was designed for.
T-Mount – The T-Mount was first developed by the Tamron lens company. It is similar to the M42 mount but with a 0.75mm thread pitch. It also was designed for a very long registration distance of 55mm which makes it a great mount to be adapted to other camera bodies. It is also commonly used to mount cameras to microscopes and telescopes.
So no you have seen just a small selection of the different lens mounts out there, you may be asking why don’t some of the big lens producers like Nikon and Canon make lenses for different mounts? Well, I wish I could tell you for certain but since I do not work for either company and am not an investigative reporter, I can only theorize on why they do this, and the arguments I have come up with seem to make sense as to why it is better for them.
A lens, despite the fact it is essentially just a tube with glass mounted in it, is a highly engineered instrument with exacting specifications. The manufacturers spend a ton of money developing lenses that work for one purposes, focus a high quality image on a single plane (film or image sensor), precisely and economically. Canon and Nikon make camera bodies and lenses. And they want the purchasers of their camera bodies, to use their lenses and vice versa. So, in their business planning, they decided to make their lenses incompatible with competitors, so you can’t natively use a Nikon lens on a Canon or a Canon lens on a Nikon body (don’t jump on me, I didn’t say there were not ways to adapt some lenses to mount on some bodies). All of this makes complete business sense. They want to lock you in. And Canon and Nikon are not the only ones who do this. Everyone does. But there is more than this. One of the biggest reasons is that they all separately designed their cameras, including registration distances and mirror clearance. Mounting a lens designed for a different camera system could potential damage the lens or the camera. While completely interchangeable parts would be a dream for photographers, it really does not make a whole lot of sense for the camera and lens makers. Companies have tried standardizing camera parts (as with the recent Four Thirds standard) but with little success. Each camera company would have to give up things they believe make their systems great. They want to make the highest quality lens possible for their specific camera. As each manufacturer has its own specifications for sensor size, mount and registration distance, they would have to completely re-engineer certain parts of their lenses in order for them to make them work on a competitor’s camera body. This ultimately may be one big reason why 3rd party manufacturer’s lenses are typically inferior to the major brand name lenses. Instead of having one set of design specs to work against, they have several, and the engineering gets complicated. However, many of these companies, such as Tokina, Sigma, and Zeiss, make some fantastic lenses for multiple camera systems. Perhaps I’ll do a post in the future on 3rd party lens manufacturers.
You now know more about lens mounts than you probably ever wanted to know, and I really only touched on some aspects, especially when you branch outside of the SLRs. The biggest message is that you should make sure a lens is compatible with your particular camera body even if coming from the same brand, or if you are adapting a different mount. In a future post I’ll talk about more considerations of adapting lenses to camera bodies as there are some aspects regarding the adapters that are relevant to different combinations, particularly one of my recent combinations, the M42 lens adapted to Nikon bodies.
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