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          3. Digital Microscope: functionality & more

          Digital Microscope

          There are many aspects to consider regarding the functionality and operation of a digital microscope.

          What is a digital microscope?

          A digital microscope is an imaging tool that uses a built-in camera with a magnifying lens, instead of eyepieces, and displays the live image on a monitor. The KEYENCE digital microscope is designed so that it is suitable for a wide range of different applications across all industries. This versatile system is mainly used in laboratories or quality assurance and research & development departments.

          KEYENCE Digital Microscope VHX-7000

          Digital Microscope – lens and image sensor system

          Digital microscopes make observation fast and convenient. They use zoom style lenses, a combination of multiple individual lenses, that make the system easier to operate compared to other microscopes: simply turn the magnification ring on the lens to adjust magnification.

          The performance of a lens is affected by these 3 main factors: depth-of-field, numerical aperature, and aberration. The KEYENCE digital microscope has a 20 times larger depth-of-field compared to conventional optical microscopes due to its naturally smaller aperture, resulting in objects always being in full focus within a large tolerance range. The ability to focus light (numerical aperature) enhances the quality of the microscope lenses and keeps aberrations, projection errors, to a minimum.

          Image captured on a conventional optical microscope (left) and Digital microscope (right)

          The KEYENCE digital microscope uses a built-in CMOS image sensor that can convert light passing through the lens into digital data and display that information in the form of an image. When the light hits the photodiodes on the surface, electron hole pairs are generated and produce electrical signs that are converted into digital form, via a transfer electrode, allowing the data taken from the CMOS sensor to be displayed on the digital microscope monitor.

          Signal path from the image sensor to the VHX-7000 digital microscope display

          Photodiodes cannot recognize colors, as a result, a color filter or prism is built into the microscope to reproduce them. The quality of the digital display ultimately depends on the color and screen resolution. The color resolution is determined by the number of pixels in the X and Y axes.

          Digital microscope: typical screen resolutions

          See volume 1 of our Introduction to Digital Microscopy guide for more on the lens and image sensor system.

          Image capturing performance of a digital microscope

          Farbspektrum einer 8-Bit Farbauflösung

          The color resolution or color depth provides the number of intensity levels that can be displayed of the 3 primary colors: red, green, and blue. For typical digital microscopes, the resolution is 8-bit with 256 x 256 x 256 color values, which allows over 16 million colors to be diplayed.

          The latest KEYENCE digital microscope has an HDR function that can capture 16-bit RGB image data, producing 256 times more data than previous models. Automatic color, brightness, contrast and texture optimization allows details of objects to be realistically displayed, while a large number of brightness levels reduce glare and enhances areas with low contrast.

          Images of a connector (100x) and a stepped stencil (2000x) in 8 and 16 bit captured with the KEYENCE digital microscope

          See volume 2 of our Introduction to Digital Microscopy guide for more on imaging capture performance.

          Depth composition of the KEYENCE digital microscope

          Depth-of-field is the area in which the object being observed is in full focus, even outside the focal point. For typical optical microscopes, the depth-of-field decreases when magnification increases. With the focusing technology of the KEYENCE digital microscope, this restriction is overcome and full focused observation is achievable even at high magnification. The depth composition function slightly moves the lens focus, extracting and stitching focused pixels, displaying a fully focused image on the digital microscope monitor across an entire field of view at any magnification.

          Extracting and stitching together the focused pixels at each level allows the KEYENCE digital microscope to create a fully focused image of the entire field of view

          See volume 3 of our Introduction to Digital Microscopy guide for more on depth composition.

          Illumination options for a digital microscope

          Digital microscopes have a dedicated light source, which allows for optimum light distribution depending on the observation distance and the lens field of view. In digital microscopy, a number of illumination techniques can be used for a wide variety of surface conditions and target object shapes.

          Punctiform illumination, known as coaxial illumination, is the best option for highly reflective surfaces or when observing the texture of an object, as it uses a half mirror to allow all the reflected light to pass through the lens in order to optimize the image display.

          Mirrors, processed metals or plastics should be observed using diffuse illumination in order to prevent high gloss in the image so that the digital microscope can illuminate the object from all directions.

          Schematic diagram of selected illumination techniques for digital microscopes: coaxial illumination (left) and diffuse illumination

          A 360° side illumination adapter allows illumination from different angles and means the display of projections and indentations on an object can be optimized. KEYENCE digital microscopes also have partial illumination to help make these projections and indentations more clearly visible.

          Finally, transparent objects can be best observed from below using transmitted light illumination. A polarizing filter also allows the reflected light to be filtered out in order to avoid specular reflection in the image.

          See volume 4 of our Introduction to Digital Microscopy guide for more on what illumination options are available on digital microscopes.

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