There seems to be a lot of confusion about camera lens mounts among photographers as nearly all camera manufacturers have launched multiple camera systems. Particularly when it comes to “throat size” and “inner diameter,” where different measurements are used to incorrectly assess a mount’s potential. Many people are misinformed about the exact sizes and shapes of mounting systems, which is why I decided to write an in-depth article about mounting systems, their differences, and take more accurate measurements for different systems to present accurate information..
1. What Is A Lens Mount ?
Lens mounts are openings on interchangeable lens cameras of a specific size that allow the attachment of lenses specifically designed for that mount. Even though cameras and lenses used to be mechanically connected, with the advent of automatic metering and autofocus systems, it became necessary to create electronic contacts on both the cameras and lenses to allow them to communicate with one another. This meant that a lens mount was no longer just a hole in a camera body; it was now more of an interface.
While bayonet mounts are the most common lens attachment system used today, other lens attachment systems such as screw-threaded lock or breech-lock have been used previously. The name “bayonet” comes from the type of fitting soldiers used on their rifles to quickly mount bayonets. Bayonet mounts use three to four tabs to lock the lens tightly in place. When using a bayonet mount, you align the marked section of the lens (usually a colored dot) with the marked section of the camera body, then twist the lens either clockwise or counterclockwise until it locks into place (depending on the brand/mount).
a spring-loaded pin locks the lens in place in its proper position, requiring the pin to be retracted when a lens is detached (which is done using a button next to the camera mount). Bayonet mounts are popular because they have several advantages over other types of mounts. For starters, it makes attaching and removing lenses a breeze. As a second benefit, it allows for a more precise and tight fit, which is critical when using high-resolution cameras, as even the slightest amount of wobble or play can distort the image. Bayonet mounts make it simple to connect lenses and cameras together via electronic contacts, allowing for two-way communication.
Considering that all camera mounts are proprietary, mounting direction, mount size, flange distance, and even the physical location of electronic contacts can vary widely between them. Let’s dig a little deeper into each of these.
2. Mounting Direction
While most lens mounts demand that lenses be attached by rotating them counter-clockwise, Nikon does it the other way around. A lens can be mounted or dismounted in any direction, but it may cause some confusion and take some time to get used to if it is mounted in the opposite direction. The mounting direction of lenses for popular camera brands is summarized in the table below.
Please note that the mounting direction is relative to the front view of the camera.
|Brand||Attaching Direction||Detaching Direction|
3. Mount Size (Throat Size, Inner and Outer Diameters)
A few critical measurements must be made when comparing lens mounts, especially when one is larger than the other (as you want to compare apples to apples). It is important to know the difference between throat size, inner diameter, and outer diameter. Let’s take a look at the differences between the various measurement criteria.
3.1 Throat Size
The lens mount’s throat size is equal to the mount’s inner diameter, minus the tabs used to attach lenses. The size of the mount’s throat tells us more about the mount’s potential and is critical when calculating the angle of incidence, which we’ll cover later.
Look at the image below to see how a system measures the throat size:
The distance between the two tabs on the inner side of the mount is what’s being measured, as you can see.
3.2 Inner Diameter
The lens opening size is represented by the inner diameter of the lens mount, which ignores the mount’s tabs. Camera manufacturers frequently provide us with this measurement to get an idea of the overall mount size.
the inner diameter of a lens mount can be seen below:
Take notice that the mount’s outermost inner portion is being measured here. There is an additional 0.5mm loss to clear the Nikon F lens’s additional recess in the inner mount. This means that while the inner diameter is 47mm, the distance between the inner parts of the mount is technically 46.5mm.
3.3 Outer Diameter
As the name implies, the outer diameter of a lens mount corresponds to the diameter of the bayonet mount, which on most cameras is where it all ends up. Because it must be able to wrap around the outside diameter of the lens’s rear portion, the mount’s outer diameter is critical in determining an approximate lens’ outer diameter.
An illustration of how a lens’s girth is determined can be seen here:
We do not measure the outer diameter of the mount from the small recess just below the outer part of it.
4. Flange Distance
“Register” refers to the distance between the lens mount’s outer mounting flange and the film/sensor plane. The term “flange distance” can also refer to the “flange focal distance,” “flange back distance,” or simply “register.” In the same way that mount throat size, inner and outer diameters, and flange distances vary greatly between camera systems, flange distances also do.
5. Mount Size, Flange Distance And The Angle Of Incidence
In light of our new understanding of mount size and the impact of flange distance on a system, it’s time to discuss the advantages and disadvantage of large and small mount sizes.
The size of the camera’s mount is critical to the overall design. Larger mounts allow for larger lenses, which in turn illuminate the sensor more effectively. As a result, optical engineers can create faster lenses. Lens design is influenced by many factors, including the mount diameter and flange distance. Because of this, lens manufacturers are now able to build simpler, smaller, lighter, and less expensive short-focus lenses instead of retro focus types because the flange distance is shorter.
A smaller flange distance allows for thinner cameras to be designed, resulting in smaller and lighter cameras. Adapters allow lenses from other camera systems with longer flange distances to be used with adapters, allowing lens designers to use a more powerful actuator for faster autofocusing. Another factor that influences lens design is the maximum angle of incidence, which is determined by throat diameter and flange distance. The larger the angle of incidence, the easier it is to make high-performance lenses, so this is something to keep in mind when designing lenses.
A disadvantage of a larger lens mount is that it will result in larger and heavier lenses. Greater throat diameter necessitates a larger lens at the mount point, increasing the thickness and weight of the lens. In addition, because sensor microlenses cannot pass enough light at extreme ray angles, a shorter flange distance can increase vignetting or discoloration in an image’s corners (although this can be mitigated by making the lens design longer to simulate a longer flange distance).
When adapting lenses from other mounts, it’s important to keep in mind that because of proprietary autofocus systems, differences in how camera bodies and lenses exchange information via electronic contacts (the number of which varies from system to system), and other issues, the majority of adapters are “dumb” adapters with manual controls, made by third-party manufacturers. In order to mount lenses from other camera mounts they developed in the past, camera manufacturers often provide adapters with the release of shorter flange distance systems, but they almost never provide adapters for competing systems.
Other lens adapters allow you to insert a lens filter (such as a neutral density or polarizing filter) and change the physical properties of the lens. This allows you to use filters on wide-angle lenses with oversized front elements without having to use bulky filter mounting rigs or large filters. Lens adapters should check the target mount’s flange distance before attaching lenses from other systems in order to ensure that infinity focus can be achieved. It is also necessary that the flange distance between the source and target systems differ sufficiently for an adapter to sit in between the lens and camera for a rudimentary converter to function properly Contacts and electronics must have more room in smart adapters so that they can communicate with the camera and the adapted lens.
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6. Camera Mount Comparison
Here are some comparisons of different camera mounts using their throat and inner diameter, flange distance, and angle of incidence as criteria:
|Description||Throat Diameter||Inner Diameter||Flange Distance||Angle of Incidence||Format|
|Leica M||40.0mm||44.0mm||27.8mm||16.05°||Full Frame|
|Minolta SR||42.0mm||45.0mm||43.5mm||11.69°||Full Frame|
|Sony E||43.6mm||46.1mm||18.0mm||28.58°||Full Frame|
|Nikon F||44.0mm||47.0mm||46.5mm||12.14°||Full Frame|
|Pentax K||44.0mm||48.0mm||45.5mm||12.40°||Full Frame|
|Leica L||48.8mm||51.0mm||19.0mm||33.13°||Full Frame|
|Canon EF||50.6mm||54.0mm||44.0mm||16.82°||Full Frame|
|Canon RF||50.6mm||54.0mm||20.0mm||33.62°||Full Frame|
|Nikon Z||52.0mm||55.0mm||16.0mm||41.19°||Full Frame|
|Fujifilm G||62.1mm||65.0mm||26.7mm||28.67°||Medium Format|
Note: To determine the incidence angle, I measured the distance between the top center of the camera sensor and the throat diameter of each system. I assumed that all full-frame sensors were 24mm high, the Fuji X camera sensor was 15.6mm high, and the Fuji G camera sensor was 32.9mm tall (note that other websites sometimes do this calculation with inner mount diameter rather than the throat diameter, and they may calculate from a corner or the center of the camera sensor rather than the top center).
7. Frequently Asked Questions
To help our readers, I’ve compiled the following list of frequently asked questions about lens mounts:
1. What are the different camera mounts ?
A wide variety of camera mounts were available in days gone by; today the most widely used camera mounts are the ones listed above plus the following: Canon EF/RF/X/G/Leica L/M/Nikon F/Z/Pentax K/Sony E. The throat diameter and flange distance vary from one to the next, making each one unique.
2. How do I know which lens mount my camera has ?
Find the brand and model of your camera, then go online and look for the manual for that camera. There should be information in the manual about the mount and a list of lenses that work with it. You can also look up the name of the lens mount on your camera by reading the description of the lens.
3. Which lens mount is the best ?
Lens mounts of all types have advantages and disadvantages, but those with the largest throat size and the shortest flange distance usually offer the most design flexibility. As of right now, the full-frame cameras with the largest throat diameter and the closest flange distance are Nikon Z, Canon RF, and Leica L models with L mounts.
4. Are all Nikon lens mounts the same ?
They’re not, in fact. The Nikon F and Nikon Z lens mounts are the only ones available for Nikon lenses. For Nikon’s older DSLR cameras, use the first, and for Nikon’s more recent mirrorless cameras, use the second.
5. Are camera lenses universal ?
They’re not, unfortunately. The majority of camera manufacturers, with the exception of a few alliances, design their own proprietary lens mounts, resulting in numerous lens options. There are lens manufacturers who make the same lens for multiple camera mounts, however.
6. Can you mount a Canon lens on a Nikon camera ?
The lens mount makes a difference. Because the flange distance on the Canon EF mount is shorter than on the Nikon F mount, you cannot use a Canon EF lens on a Nikon F camera. The Canon RF lens can, however, be used with a Nikon Z camera.
7. What is a lens mount adapter ?
With a lens adapter, a lens from one mount can be used with another mount on a camera. Lens mount adapters with full compatibility and autofocus features are available from some manufacturers, but most are “dumb” and unable to transmit electronic data.