C-mount is the most common optics mount in the industrial market. It is defined by a flange focal distance of 17.526 mm, a diameter of 1” (25.4 mm) with 32 threads per inch.

The automatic cropping of lenses designed for use with APS-C sized sensors on a full frame camera can be disabled. This gives you a good idea of the reduced image circle that these lenses offer when cropping is disabled:

You can't use a lens designed for one lens mount on a different lens mount as the lens just won't fit. E.g. you can't use a Canon lens on a Nikon camera. Sometimes an a adapter can be used, but we'll look at this later.

Equivalentfocal lengthcalculator

Of course, cropping the image means you loose image data compared to what you would capture with a lens designed for use with full frame cameras. A DT lens used on the 24.6MP Sony A900 will only produce an 11MP image. The rest of the image has to be cropped away to compensate for the lens' reduced image circle.

This is why a spacer kit is supplied with Opto Engineering® telecentric lenses including instructions on how to tune the back focal length at the optimal value.

However, you can (in some cases) get adapters that let you use a lens designed for a lens mount with a shorter flange distance than the mount your camera uses. There are two types of these adapters.

The main features of most optical systems can be calculated with a few parameters, provided that some approximation is accepted. The paraxial approximation requires that only rays entering the optical system at small angles with respect to the optical axis are taken into account. The thin lens approximation requires the lens thickness to be considerably smaller than the radii of curvature of the lens surfaces: it is thus possible to ignore optical effects due to the real thickness of the lenses and to simplify ray-tracing calculations. Furthermore, assuming that both object and image space are in the same medium (e.g. air), we get the following fundamental equation:

Mxx-mounts are different types of camera mounts defined by their diameter (e.g. M72, M42), thread pitch (e.g. 1 mm, 0.75 mm) and flange focal distance. They are a common alternative to the F-mount for larger sensors.

For cameras with full frame sensors, they cannot properly use a lens designed for use with an APS-C sensored camera. The image circle produced by the lens is just not big enough to cover the full frame sensor.

The number and placement of CPU contacts varies between each type of lens mount. Also, the signals sent through the contacts is different.

Some mechanical mounts feature a screw drive motor used for autofocusing the lens. (See section below on Autofocus motors for more information). In the Nikon F mount photo, the camera was set to manual focus, and so the "screw driver" is recessed in the body, in autofocus mode it would pop out.

FoVcalculation

But, the sensor size used in the first DSLRs (and still used in many today) was smaller than a frame of 35mm film used in film SLRs. This was mostly due to the high costs of large sensor fabrication.

If you are considering purchasing a camera that accepts interchangeable lenses, you need to be aware of compatibility issues. Buying a camera and lens and then finding they don't work properly together could be quite annoying.

After a few years, technology improved, and it became possible to produce full frame image sensors, the same size as a frame of 35mm film at a reasonable cost. And so we today have a situation where cameras with different sensor sizes both use the same lens mount, and lenses designed for different sensor sizes both use the same lens mount.

Mechanical mounts like the Nikon F mount often have an aperture lever. This is to allow controlling the aperture of the lens from the camera. Electronic mounts still allow this, just the control is done via sending an electrical signal to the lens rather than mechanically.

Mirrorless cameras tend to have quite a short flange distance because they don't need any room behind the lens mount for a mirror. This has made them quite popular for mounting old lenses on, and there are a wide range of adapters for using different mount lenses on the micro four thirds and Sony E mount (NEX) cameras.

These sorts of adapters are only available for lens mounts where there is a small difference between the two flange distances. A common one is an adapter that lets you use Canon FD mount lenses on a Canon EF mount body. The FD mount has a flange distance of 42 mm, while the EF mount has a flange distance of 44 mm.

It is also worth noting that manufacturers can license a lens mount. For example, Fuji produced several DSLR cameras that used the Nikon F mount. And Kodak produced a couple of cameras that were available in both Canon EF and Nikon F mount versions.

The basic purpose of a lens of any kind is to collect the light scattered by an object and recreate an image of the object on a light-sensitive ‘sensor’ (usually CCD or CMOS based).

For example, a Canon 600D DSLR has an APS-C sized sensor and uses the Canon EF mount. It can accept lenses that use the EF mount and are designed for use with APS-C sized sensors (EF-S / Di II / DC / DX depending on the lens manufacturer). It can also accept lenses that use the EF mount and are designed for use with 35mm film cameras or full frame digital cameras.

So if you have a full frame camera, or might want to purchase one in the future, you need to consider this when looking at lenses.

Since fixed focal length lenses also follow the previous equation, it is possible to calculate the required focal length given the magnification and working distance, or the required working distance given the sensor size, field of view and focal length, etc. (some examples are given at the end of this section). For macro and telecentric lenses instead, the working distance and magnification are typically fixed.

Most lens mounts use a pin on the camera body that inserts into a hole on the lens to lock the lens in place. To remove the lens, press the lens release button on the camera body. This retracts the locking pin. With the button held down, you can then rotate the lens back and remove it from the camera.

Different mechanical mounting systems are used to connect a lens to a camera, ensuring both good focus and image stability. The mount is defined by the mechanical depth of the mechanics (flange focal distance), along with its diameter and thread pitch (if present). It’s important that the lens flange focal distance and the camera mount flange distance are exactly the same, or focusing issues may arise. The presence of a threaded mechanism allows some adjustment to the back focal distance if needed. For example, in the Opto Engineering® PCHI series lenses, the back focal adjustment is needed to adjust the focus for a different field of view.

However, the lens mount does become more important if you are looking to use older (and cheaper) manual lenses. It is also important when buying a lens to check that it is compatible with your camera. For most people though, the type of lens mount a camera uses is worth considering, but probably quite far down on the list of important features.

It is also important to remember that when you buy into a camera that offers interchangeable lenses, you are buying into a system. So you need to consider carefully the range of lenses available in that system.

fov是什么

After a while, the manufacturers started to produce lenses specially to fit the reduced sensor size of their digital cameras. This made the lenses smaller and cheaper to manufacture. These lenses covered the smaller size of the digital sensors, but did not produce an image circle large enough to cover a frame of 35mm film.

For common optical systems, in thin lens approximation, the focal length is the distance over which collimated rays coming from infinity converge to a point on the optical axis.

35mm equivalentfocal length

The majority of links on this website are affiliate links. This means that I earn a commission if you purchase a product through one of these links. The product will still cost you the same as if you went direct, and the commission helps pay for running this site.

Typical F-numbers are F/1.0, F/1.4, F/2, F/2.8, F/4, F/5.6, F/8, F/11, F/16, F/22, etc. Every increment in the F-number (smaller aperture) reduces incoming light by a factor of 2. The given definition of F-number applies to fixed focal length lenses where the object is located ‘at infinity’ (i.e. a distance much greater than its focal length). For macro and telecentric lenses where objects are at a closer distance, instead, the working F/# (wF/#)is used. This is defined as:

The first thing to note is that each camera manufacturer typically has their own lens mount that they use on their cameras.

Canon's EF mount uses a purely electronic linkage with the lens, so all lenses for the EF mount contain a built in focus motor.

The CPU contacts on the lens and lens mount connect together so that the camera can communicate information to the lens. In the examples above you can see Nikon uses spring loaded pins in the lens, while Canon uses spring loaded pins in the camera. When the lens is locked into position, the pins touch the contacts to allow electrical signals between the body and lens.

The "screw driver" is spring loaded, so you can mount lenses without it scratching the mount as you rotate the lens to lock it in place. On the lens you can see the corresponding "screw" that the "screw driver" slots into.

On Canon EF-S lenses, they modified the mount on the lens slightly, so they cannot be mounted on a full frame camera with EF mount. For Sony and Nikon, their DT and DX lenses can be mounted on full frame cameras, and the camera will crop the images to the same size as an APS-C sensor.

VAT IT02011230204 Fiscal code and registration number at Mantova Business Register 02011230204 Nr. REA: MN-216669 - Share Capital: 205.258,00 € 沪ICP备12040578号-2

The F-number affects the optics depth of field (DoF), that is the range between the nearest and farthest location where an object is acceptably in focus. Depth of field is quite a misleading concept because physically there is one and only one plane in object space that is conjugate to the sensor plane. However, being mindful of diffraction, aberration and pixel size, we can define an “acceptable focusing distance” from the image conjugate plane, based on subjective criteria. For example, for a given lens, the acceptable focusing distance for a precision gauging application requiring a very sharp image is smaller than for a coarse visual inspection application.

Different lens mounts use a different flange distance. The flange distance, also known as the register distance, is the distance between the lens mount and the camera sensor (where the rays from the lens will be focused).

It won't work the other way round, of course. You can't have an adapter that removes 26.21 mm from the Pentax K mount to allow you to use micro four thirds lenses. The lenses would have to go inside the mount!

For optical systems used in machine vision, in which rays reflected from a faraway object are focused onto the sensor plane, the focal length can be also seen as a measure of how much area is imaged on the sensor (Field of View): the longer the focal length, the smaller the FoV and vice versa (this is not completely true for some particular optical systems, e.g. in astronomy and microscopy).

FOV to focal lengthcalculator

Although these manufacturers produce lenses in multiple mounts, the mount on the lens is not interchangeable. So you can't buy a Sigma lens designed for use with Canon EF mount and then use it on a Nikon F mount camera. Instead you'd need to buy the Nikon F mount version of the lens.

In this article we'll look at the different compatibility issues you might come across, and also how some cameras can be used with a wider range of lenses via adapters.

Tagged with Digital Single Lens Reflex cameras, DSLRS, Flange distance, Interchangeable Lenses, Lens mount adapters, Lens mounts, MILCs, Mirrorless cameras, Single Lens Translucent Cameras, SLTs, Using old manual lenses

The image sensors used in DSLRs were about the same size as a piece of APS-C film. So they are known as APS-C sized sensors.

The focal length is a typical characteristic of an optical system. It is a measure of how strongly the system converges or diverges rays of light. If collimated rays converge to a physical point, the lens is said to be positive (convex), whereas if rays diverge the focus point is virtual and the lens is said to be negative (concave). All optics used in machine vision applications are overall positive, i.e. they focus incoming light onto the sensor plane. CCTV lenses are commonly identified by their focal length, expressed in millimeters (12mm, 25mm, 35mm, etc.).

For example, the Micro four thirds lens mount has a flange distance of 19.25 mm, while the Pentax K mount has a flange distance of 45.46 mm. So, by using an adapter with a width of 26.21 mm (19.25 + 26.21 = 45.46), a Pentax K mount lens can be used on a micro four thirds lens mount.

The four thirds, micro four thirds, Nikon CX, Sony E, and Samsung NX mounts are all new 'designed for digital' mounts that have no hold-over from the days of film cameras. So if you have or are thinking buying a camera with one of these mounts, you can safely skip over this section.

But if you have or are thinking of buying a camera with the Canon EF, Nikon F, Sony A, or Pentax K mount, then this section is worth a read.

A certain number of parameters must be considered when choosing optics, depending on the area that must be imaged (field of view), the thickness of the object or features of interest (depth of field), the lens to object distance (working distance), the intensity of light, the optics type (telecentric/entocentric/pericentric), etc.

The first acts like an extension tube, so the lens can focus closer, but you lose infinity focus (can't focus on things further away).

Every optical system is characterized by an aperture stop, that determines the amount of light that passes through it. For a given aperture diameter d and focal length f we can calculate the optics F-number:

Nikon meanwhile uses a combination electronic and mechanical mount. Below you can see a Nikon F mount lens and the F mount on the camera.

fov和焦距的关系

As a general rule, a lens mount with a smaller flange distance can use lenses designed for use with a mount with a larger flange distance, provided the correct adapter is used. The exception to this is with some lenses where the rear protrudes back inside the camera. These can cause a problem with DSLRs and SLTs as the rear of the lens might hit against the camera's mirror.

CS-mount is a less popular and 5 mm shorter version of the C-mount, with a flange focal distance of 12.526 mm. A CS-mount camera presents various issues when used together with C-mount optics, especially if the latter is designed to work at a precise back focal distance.

where s (s’ ) is the object (image) position with respect to the lens, customarily designated by a negative (positive) value, and f is the focal length of the optical system (cf. Fig. 1). The distance from the object to the front lens is called working distance, while the distance from the rear lens to the sensor is called back focal distance. Henceforth, we will be presenting some useful concepts and formulas based on this simplified model, unless otherwise stated.

The lens mount a camera uses affects what lenses you can use with that camera. Most lens mounts have a wide range of different lenses available, and so consideration of the lens mount is not particularly important.

Many cameras are found not to respect the industrial standard for C-mount (17.52 mm), which defines the flange-to-detector distance (flange focal length). Besides all the issues involved with mechanical inaccuracy, many manufacturers don’t take into the due account the thickness of the detector’s protection glass which, no matter how thin, is still part of the actual flange to detector distance.

FOVcalculator

So it is best the check the specification of the lens if you want to be sure whether or not it includes a built in autofocus motor. All Canon and third party autofocus lenses for the Canon EF mount feature a built-in focus motor.

Some lens mounts use a purely electronic connection to the lens, while other mounts use a combination of electronic and mechanical connections. Below you can see a Canon EF mount lens, and the EF mount on the camera. The Canon EF mount is an electronic mount.

F-mount is a bayonet-style mount originally developed by Nikon for its 35 mm format cameras and is still found in most of its digital SLR cameras. It is commonly used with bigger sensors, e.g. full-frame or line-scan cameras. Lenses can be easily swapped out thanks to the bayonet mount, but no back focal adjustment is possible.

The main issue is the coverage of the lens. When digital cameras were first introduced, most of the manufacturers (with the exception of Olympus) carried on using the same lens mounts they had been using for their film cameras.

With Pentax cameras, you don't (currently) need to worry about whether a lens will be compatible with your camera or not. All Pentax DSLRs use an APS-C sized sensor, and so are compatible with lenses that use the K mount, whether they cover APS-C or full frame.

Focal length

A common F-number value is F/8 since smaller apertures could give rise to diffraction limitations, while lenses with larger apertures are more affected by optical aberrations and distortion. A rough estimate of the field depth of telecentric and macro lenses (or fixed focal length lenses used in macro configuration) is given by the following formula:

So if you might be interested in using older manual lenses with your digital camera, it is a good idea to check the flange distance for the mount of the camera you are looking at. You can see a good list of different lens mounts and their flange distances at Wikipedia: Flange focal distance.

Some lenses feature built in autofocus motors, while other lenses use what's known as a screw drive, which is driven by a motor in the camera body. Not all camera bodies feature screw drive motors.

Each camera mount is more commonly used with certain camera sensor formats. The most typical sensor formats are listed below. It is important to remember that these are not absolute values – i.e. two cameras listed with the same sensor format may differ substantially from one another in terms of aspect ratio (even if they have the same sensor diagonal). For example, the Sony Pregius IMX250 sensor is listed as 2/3” and has an active area of 8.45 mm x 7.07 mm. The CMOSIS CMV2000 sensor is also listed as 2/3” format but has an active area of 11.26 mm x 5.98 mm.

Pentax's KAF2 mount provides a screw drive motor and works with K mount lenses that have a built in focus motor as well.

where p is the sensor pixel size (in microns), M is the lens magnification and k is a dimensionless parameter that depends on the application (reasonable values are 0.008 for measurement applications and 0.015 for defect inspection). For example, taking p = 5.5 µm and k = 0.015, a lens with 0.25X mag and WF/# = 8 has an approximate DoF = 10.5 mm.

So if you buy a lens that relies on the screw drive motor of the camera body, but the camera body doesn't have a motor, then you won't be able to autofocus with that lens.

The focal length and the focus plane coincide only when the object is placed at an infinite distance, indeed beams from a point on the object can be considered as parallel. When instead the distance from the object is ‘short’ (rule of thumb: <10x Focal length), we are in macro mode and the focus plane is placed further away from the optical system compared to the focal length.

For cameras with APS-C sized sensors, they can accept both 'designed for APS-C' lenses, and lenses designed to cover the image circle covered by 35mm film (full frame).

A camera with a short flange distance can use lenses meant for a camera with a larger flange distance by use of an adapter. The adapter adds the extra distance needed so that the lens can focus correctly.

Each camera manufacturer typically produces lenses designed only for their own lens mounts. There are also a number of third party manufacturers who produce lenses for a variety of mounts. The main lens manufacturers are Sigma, Tokina, and Tamron.

All current lens mounts use a bayonet type fitting. You line up a marking on the lens with a marking on the camera body, and the lens can then be slotted into the mount on the camera. Then the lens is rotated (whether left or right depends on the lens mount), until it locks into place.

Both Nikon and Sony vary as to whether their camera bodies include a built in screw drive motor. Some do, some don't. Typically their cheapest models don't include a built in motor, and will only autofocus with lenses that have a built in motor.

Macro and telecentric lenses are designed to work at a distance comparable to their focal length (finite conjugates), while fixed focal length lenses are designed to image objects located at a much greater distance than their focal length (infinite conjugates). It is thus convenient to classify the first group by their magnification, which makes it easier to choose the proper lens given the sensor and object size, and the latter by their focal length.

There are a large number of old lenses designed for use with lens mounts that are no longer in common use. That means these lenses can often be picked up fairly cheap. When used on a different lens mount via an adapter, they will always be manual focus, and you will also need to control the aperture manually. (Old lenses have an aperture ring you use to set the aperture).

Another thing to note is that the camera manufacturers also produce different versions of their lenses and lens mounts that are not fully compatible with each other.

The other type of adapter includes corrective glass, so you retain infinity focus. This usually works like a teleconverter, so the image is magnified / cropped compared to what it should be. The extra glass in these adapters usually reduces image quality as well.

Note that Tokina do not have a special designation to show that the lens features a built in motor. Similarly, some Sigma and Tamron lenses may have a built in motor but not feature the HSM / PZD / USD designations. (The designations actually refer to the type of autofocus motor used in the lens).

As a note to the above table, Samsung produced a couple of K mount lenses for use with APS-C sized sensors, but their lenses are not specifically labeled as such. Samsung also licensed the Schneider-Kreuznach name for use on some re-badged Pentax K mount lenses, again these lenses are not labeled as to whether they are designed for use with APS-C cameras.