If you ever wondered why you can’t interchange lenses between different manufacturers, this article is for you. What stops this simple act is lens mounts.
In this article, you’ll find out what lens mounts are, what types exist, and how you might be able to use them to your benefit.
What Is a Lens Mount?
A lens mount is the opening of an interchangeable lens that allows it to connect with the camera. When a lens mount works, the lens attaches to the camera body without falling off.
In former times, lenses attached mechanically to the camera. This meant there was no communication between the two pieces.
Due to our age of digital photography, we need a system that is able to communicate, and well. Electronic contacts on the lens and camera allow automatic metering and autofocus systems to work.
Nowadays, lens mounts aren’t only mechanical, but electronic too.
Types of Lens Mounts
Today, every photography lens has a bayonet mount. The word ‘bayonet’ is a knife or spike-shaped weapon designed to fit on the end of a rifle’s muzzle. This allows it to be used as a spear.
These mounts use three to four tabs that allow the lens to lock tightly in place. Other lens mounts were used in the past, such as screw-threaded lock and breech-lock.
Typically, with a bayonet mount, the user lines up a colored dot on the lens to the same dot found on the camera body. When coupled, the lens needs a turn of 45-90% to lock into place.
The locking mechanism here is mechanical. A spring-loaded pin locks the lens into place in its correct position.
When the lens needs detaching, the pin retracts. This is completed by the use of a button next to the lens mount, on the camera body.
We use the bayonet lens mount because of its advantages compared to other types. First, it makes the attaching and detaching of lenses quickly and easily.
Secondly, it allows for a tight and precise fit. This is important with modern cameras, as any ‘play’ could end up affecting parts of the images.
Lastly, the bayonet mount allows the incorporation of electronic contacts. This allows two-way communication between the two pieces.
All lenses have a bayonet mount. But that doesn’t mean you can use lenses across different manufacturers. A Sony lens will not fit onto a Canon DSLR body.
Differences in Lens Mounts
Apart from the size of the bayonet mount, there are other factors that keep lenses from moving across manufacturers. The number of tabs in a specific lens mount varies from brand to brand.
Even if three is a preferred number, they allow the lens to rotate a specific way. Some go clockwise, others are the opposite. Also, the incorporation of electronic contacts is unique across brands.
Furthermore, the most important element in lens mounts is the flange focal distance.
Flange Focal Distance
The Flange Focal Distance is a measurement. It describes the length between the mounting flange (edge of the lens mount on the camera body) to the image sensor or film plane.
These differ between manufacturers. Even if you could fit a Nikon lens on a Canon DSLR with the bayonet mounts and electronic contacts, it won’t focus to infinity.
This measurement is usually the first thing designers use when creating a new lens. To fix this problem, you can use adapters.
We have discussed lenses working across different manufacturers. But there is a way where they can be used. After all, companies such as Sigma, Tamron, and Zeiss make the same lenses for different camera bodies.
These are what we call third-party lens manufacturers. They don’t create cameras, instead, creating lenses for other camera companies to use. I use my Canon 5D Mark III camera with Tamron and Sigma lenses.
For those who want to use a cross-over system of lenses and cameras from different manufacturers, there is still hope. Adapters allow you to do just that.
There aren’t adapters available for every system, but there are quite a few. There are also quite a few reasons why you might want to mix together different brands, as some are better than others in different areas.
Adapters work in one instance; when the lens has a longer FFD than the camera body. Here, the lens adapter makes up the difference in local flange distance between the camera and lens.
For example, a Nikon F lens to Sony E adapter makes up the difference of 28.5mm. This is to provide the proper total 46.5mm of focal flange distance. This allows a proper infinity focus.
There are adapters for lenses that work for lenses with a shorter FFD than the camera body. But you won’t be able to achieve infinity focus unless there is a corrective element in place.
These adapters maintain electronic communication between the lens and camera. There are also ‘dandelion chips’. This allows adapters of retaining the lens’s autofocus and image stabilization.
One adapter that gained traction recently is that for APS-C and smaller sensor sized cameras. They associate with terms like ‘crop factor‘ and ‘equivalent focal length’.
When it comes to the mount size, there are three important measurements. They are useful when comparing different lenses. The three measurements are the throat size, inner diameter, and outer diameter.
The throat size is the innermost measurement of the camera’s lens opening, minus the locking tabs. the throat size gives the most accurate representation of the mount.
It is also useful for calculating the angle of incidence.
You find this measurement from the space between the tabs. For the Canon 5D Mark IV, the throat size is 50.6 mm.
The inner diameter represents the size of the opening, without taking into account the locking tabs. The measurement is the one camera manufacturers are most likely to provide.
This gives us a size of the lens mount. For the Canon 5D Mark IV, the inner diameter is 54.0 mm. This gives us the size of the tabs, which are 3.4mm together, or 1.7mm each.
The outer diameter of the lens mount is the full diameter of the bayonet mount. This is the end of the metal mount.
This size is very important in determining the approximate outer diameter of the rear part of the lens. This size is around 10 mm.
The flange distance is also known as ‘flange focal distance’, ‘flange back distance’ or ‘register’. this is the distance between the mounting flange and the film/sensor plane.
For those that don’t know what a mounting flange is, it is the distance of the outer most part of the lens mount, when viewed from the side.
Different mounts have different sizes. Flange mounts also differ across camera systems and manufacturers.
Angle of Incidence
The size of the mount is an important factor for any camera system. A larger mount size allows for a larger lens, allowing more light to hit the sensor. Bigger mounts allow engineers to create faster lenses.
Yet, the mount diameter is not the only variable that impacts the lens design. The other measurement that is very important is the flange distance.
A shorter flange distance allows the placement of lenses closer to the film or sensor. This allows manufacturers to build simpler, smaller and lighter short focal lenses.
Also, with a shorter flange distance means a thinner, lighter camera body. On top of this, you can fit lenses with powerful actuators. These allow for faster autofocusing.
The benefit of a shorter flange distance allows the use of lenses with a larger flange distance. This is by use of an adapter.
|Description||Throat Diameter||Inner Diameter||Flange Distance||Angle of Incidence||Format|
|Canon EF||50.6mm||54.0mm||44.0mm||16.82°||Full Frame|
|Canon RF||50.6mm||54.0mm||20.0mm||33.62°||Full Frame|
|Fujifilm G||62.1mm||65.0mm||26.7mm||28.67°||Medium Format|
|Leica L||48.8mm||51.0mm||19.0mm||33.13°||Full Frame|
|Leica M||40.0mm||44.0mm||27.8mm||16.05°||Full Frame|
|Minolta SR||42.0mm||45.0mm||43.5mm||11.69°||Full Frame|
|Nikon F||44.0mm||47.0mm||46.5mm||12.14°||Full Frame|
|Nikon Z||52.0mm||55.0mm||16.0mm||41.19°||Full Frame|
|Pentax K||44.0mm||48.0mm||45.5mm||12.40°||Full Frame|
|Sony E||43.6mm||46.1mm||18.0mm||28.58°||Full Frame|
The throat diameter combined with the flange distance determine the greatest angle of incidence.
The angle of incidence is the angle at which light hits the less.
When we use lenses on cameras that don’t share the same manufacturer, the lens acts in a different way. This isn’t hard to imagine. Although the lenses fit on the camera, they have different optics at different positions inside them.
The larger the angle of incidence, the more light bending happens.