A camera with 25 mm diagonal FOV can only image an area this large if the magnification is 1x. With a typical life science magnification of 40x, the camera FOV decreases by a factor of 40, resulting in a 625 µm diagonal FOV.

FOV cameramodel

For keeping the objective at the proper position, there are mounting threads on almost all objectives. Commonly used mounting threads include RMS, M25 x 0.75, M26X 0.706, M32 x 0.75.

FOVto focal length calculator

Field of View is the area of the object that can be imaged by a microscopy system. The size of the field of view is determined by the objective magnification or focal length of the tube lens for an infinite-corrected objective. In a camera system, the field of view of the objective is related to the sensor size.

At Shanghai Optics, we design and manufacture custom objectives and imaging systems to support our customers’ needs in many industries, including medical, biomedical, machine version, scientific research, and metrology, etc. Taking the client’s budget and precision requirements into consideration, our experienced engineering team ensure that each design can be manufactured at a reasonable cost and the optical performance is being met based on fabrication, assembly, and alignment tolerance analysis.

Field of view definition microscope

Each microscope objective is itself a complex assembly of lenses, and besides contributing to the magnification, it is the objective lens which determines the resolution power of the microscope. An objective lens can also provide optical aberration corrections.  A reflective objective, for instance, includes two mirrors within the assembly. These mirrors can focus laser light as well as provide chromatic corrections.

The area across which your camera can image is known as the field of view or FOV, the larger the FOV the more of your sample you can see. Having a large FOV allows you to take more efficient images containing more data, and take fewer images in order to capture the entire sample. But as with all camera specifications, changes to FOV will affect other vital factors such as resolution and imaging speed.

Field of view human eye

Magnification is one important parameter. Magnification is usually denoted by an X next to a numeric value.  Objectives are available in a range of magnifications from 2X to 200X.

Two major lens components—the objective lens and the ocular lens, or eyepiece—work together to project the image of the specimen onto a sensor. This may be the human eye or a digital sensor, depending on the microscope setup.

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CMOS cameras offer much larger sensors, typically around 18.8 mm diagonal which matches up well to certain microscope models. Some microscopes can go above 20 mm diagonal, so CMOS cameras are also available with sensor sizes of 22 mm, 25 mm, and even 29 mm.

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By recognizing that FOV requirements can be highly variable, we are able to better serve the needs of our customers and offer a broad range of camera FOV options.

Many objectives are designed to be used with a cover glass. Using an incorrect coverslip thickness can greatly reduce the optical performance of a microscopy system.

The development of larger FOV microscopes and scientific cameras that can take advantage of the F-mount is relatively recent - at the time of writing only one commercially available 25 mm microscope exists. Most modern microscopes have a 19 mm or 22 mm FOV and are therefore still able to use the C-mount. The largest format spinning disk confocal systems are also limited to a 22 mm FOV.

The ocular lens, located at the top of a standard microscope and close to the sensor (receiving eye) receives the real image from the ocular lens, magnifies the image received and relays a virtual image to the sensor. While most eyepieces magnify 10x, there are some which provide no magnification and others which magnify as much as 30x. The magnification power of the microscope can be calculated by multiplying the magnification power of the eyepiece, or ocular lens, by the magnification power of the objective lens. For example, an objective lens with a magnification of 10x used in combination with a standard eyepiece (magnification 10x) would project an image of the specimen magnified 100x.

While the simplest of microscopes is simply a magnifying glass with a single lens, compound microscopes used today are highly complex devices with a carefully designed series of lenses, filters, polarizers, beamsplitters, sensors, and perhaps even illumination sources. The exact combination of optical components used will depend on the application of the microscope; the wavelength of light with which it is intended to be used, and the resolution and magnification required in the final image.

where θ is the maximum 1/2 acceptance ray angle of the objective, and n is the index of refraction of the immersion medium. Figure 2 shows the ray angle θ of an infinity-corrected objective.

Camera FOVcalculator

Microscope Objectives or Objective lenses are in many ways the heart of the microscope, and are typically mounted on a rotating nosepiece or turret to enable easy selection. Many microscopes will be equipped with a scanning objective (4x), a low power objective (10x), a high power objective (40x), and perhaps even an oil immersion objective lens.

These larger sensors typically have more pixels, so while an EMCCD would have 0.25 megapixels (MP), CMOS cameras contain anywhere from 1-15 MP depending on the pixel size.

Since indirect backlight illumination is generally more effective than direct illumination, most microscopes do not include an internal light source.  Instead, they rely on daylight or on background illumination such as a lightbulb. In brightfield illumination, also known as Koehler illumination, two convex lenses saturate the specimen with external light admitted from behind. These two lenses, the collector lens and condenser lens, work together to provide a bright, even, and constant light throughout the system: on the image plane as well as on the object plane.  This system of illumination is used in many compound microscopes, including student microscopes and those found in many research labs.

The greater the magnification, the smaller the FOV, as shown in Figure 2. However, high resolutions depend on high magnifications (see our resolution article for more), and high camera speeds can also be obtained with smaller FOVs. So in order to image at a large FOV, it will affect other factors in your imaging. Luckily, most biological samples are small (from cells to molecules) and often don 't need the entire FOV the camera can offer.

A microscope objective is an important component of a microscopy or imaging system for a range of science research, biological, industrial, and general lab applications.. An objective lens determines the basic performance of an optical microscope or imaging systems and is designed for various performance needs and applications. It is located closest to the object and is an important component in imaging an object onto the human eye or an image sensor.

Since the objective is closest to the specimen being examined, it will relay a real image to the ocular lens. While doing so, it contributes a base magnification of anywhere from 4x (for a scanning objective lens, typically used to provide an overview of a sample) to 100x (for oil immersion objectives).

The camera FOV depends on two factors: the size of the camera sensor and the total magnification. Sensor size can be measured in a number of ways but a commonly used measure is the size of the diagonal across a sensor, as some sensors are square and others rectangular. This is typically displayed in millimeters, and a range of camera sensor sizes can be seen in Figure 1.

The optical aberration correction determines the optical performance of an objective lens and plays a central role in the image quality and measurement accuracy of imaging or microscopy systems. According to the degrees of the aberration corrections, objective lenses are generally classified into five basic types: Achromat, Plan Achromat, Plan Fluorite (Plan Semi-Apochromat), Plan Apochromat, and Super Apochromat.

Important specifications are marked on the barrel of the objective, so students or researchers can easily identify the properties of an objective and determine the optical performance and working conditions for proper use. Figure 1 shows a diagram of an objective lens. A detailed discussion of the objection specifications is provided below.

FOVfull form

CCDs and EMCCDs typically had smaller sensors measuring around 11 mm, this limits what you can image and is well below the maximum of most microscopes.

Figure 1: Different camera FOVs displayed on the same sample. While CCD/EMCCDs have small FOVs, CMOS cameras range from 18.8-29 mm in FOV, and can be square or rectangular.

Some rectangular camera sensors can often occupy the microscope FOV more effectively depending on the size, but if the camera FOV is larger than the microscope FOV there will be vignetting, an effect seen at the corners of the image due to the lack of light, as seen in Fig.3 Bot. While this may capture more of the microscope FOV, the substantial image artifacts at the corners of each image can lead to decreased image quality.

If the goal is simply to attach the camera to the microscope, a 1x adaptor contains no additional lenses and provides no additional magnification or demagnification. This is often the preferred method as it introduces no additional lenses into the system. Every extra lens reduces the number of photons reaching the camera by 3-4% so many researchers will try to avoid this.

A microscope is a special optical device designed to magnify the image of an object. Depending on the type of microscope, it may project the image either onto a human eye or onto a recording or video device. As an example, consider the photographs of cells that can be found in a science textbook. These photographs have all been taken by a specialized microscope, and may be called micrographs.

The ocular lens, or eyepiece, is also an optical assembly rather than a single lens, but it is typically more simple than the objective. Often it is composed of two lenses: a field lens and an eye lens. The design of the ocular lens determines the field of view of the microscope, as well as contributing to the total magnification of the system.

A simple magnifier (magnifying glass), works when the object to be examined is situated within focal length of the magnifier lens, enabling larger virtual image is produced. This type of magnifier is very limited in both resolution and magnification. A compound microscope, on the other hand, uses a relay lens system instead of the single lens, and since each lens component can contribute magnifying power, the result is greatly increased capability.

The parfocal length is the distance between the objective mounting plane and the specimen / object. This is another specification that can often vary by manufacturer.

A microscope C-mount or F-mount adaptor is needed to connect a scientific camera to the microscope camera port. The mount threading is standardized which means that a C-mount adaptor will connect to all scientific cameras that connect via C-mount. However, the adaptors are microscope specific which means that although any C-mount camera will connect to a C-mount adaptor, the adaptor will only fit microscopes of the matching brand.

At Teledyne Photometrics, we aim to create cameras that can optimally match the FOV of all modern microscopes (Table 1). For this reason, the Prime 95B Series comprises a 19 mm camera, a 22 mm camera and a 25 mm camera. Additionally, the Prime BSI and Iris 9 both fit a 19 mm microscope FOV and the Iris 15 fits a 25 mm microscope FOV. The Kinetix is our largest format sensor which is able to be used to get the maximum FOV out of any system up to 29 mm.

Most objectives are designed to image specimens with air as the medium between the objective and the cover glass. However, for achieving higher working numerical apertures, some objectives are designed to image the specimen through another medium such as special oil with a refractive index of 1.51.

Figure 3: Matching camera FOV to microscope FOV. Top . An 18 mm FOV microscope is matchedby an 18 mm FOV camera, which fits within the microscope circular FOV. Bot . Having a camerawith a larger FOV than the microscope leads to more image capture but introduces vignetting artifacts.

Adaptors can also affect the microscope and camera FOV depending on the type of adaptor used. A C-mount adaptor is the most popular microscope camera adaptor and is restricted to a maximum 22 mm FOV. The F-mount adaptor is a larger format adaptor capable of reaching >30 mm FOV.

The field of view of the camera determines how much of your sample you can see. With larger FOVs, cameras can image more effectively and capture a sample in fewer images. However, FOV is decreased at higher magnifications and in order to improve speed, and it should be matched to the model of microscope. By keeping this in mind, you can maximize your FOV and perform more efficient imaging.

Adapters can have lenses in them to magnify or demagnify the image before it reaches the camera. This can be used to better match the camera FOV to the microscope FOV. For example, if the camera has an 11 mm diagonal FOV but the microscope is capable of an 18 mm FOV, a 0.67x adaptor would demagnify the image and allow it to be displayed on the 11 mm camera. However, this increase in FOV comes at the cost of reduced resolution.

Similarly to resolution, FOV is dependent on both the microscope and the camera, both of which have upper limits on their max FOV. By pairing a large FOV camera with a large FOV microscope much of your sample can be captured at once, while using a smaller FOV camera with a large FOV microscope will limit the amount of data you can receive even if the microscope can deliver much more.

Camerafield of view simulator

Objective lenses can be classified based on the objective construction, field of use, microscopy method, performance (optical aberration corrections), and magnification. Many microscope objective manufacturers offer a wide range of objective designs, which provide various degrees of optical aberration corrections for supporting different needs. Mirrors or reflective elements are used in objective lenses for the applications that requires chromatic aberration over board spectral ranges. Most traditional microscopy systems use refractive objectives such as achromatic objectives (the cheaper objectives) for laboratory microscope applications and plan apochromats (expensive objectives) for biological and science research microscope applications.

One thing to keep in mind is that a microscope FOV is circular, and a camera FOV is square/rectangular, as seen in Fig.3 Top. Pairing an 18 mm FOV camera with a 18 mm FOV microscope does result in some areas that are not imaged, but this is largely a common factor with all imaging systems unless circular camera sensors emerge in the future. So for now, the camera FOV should aim to fit within the microscope FOV, meaning that it is best to match the FOV between camera and microscope.

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Objectives are complex multi-element lenses. For any given application, careful consideration of the optical parameters and specifications is necessary. In many cases, custom-designed objective assemblies provide the best-fit solution for meeting all the requirements of a specialized application.  Custom parameters may include antireflection coatings, chromatic focus shift, working distance, image quality (MTF and spot size), lens mount, glass window thickness, and field of view, among others.