Digital Microscope | Working | Steps to Use | 2 Important Measurement types



What are digital microscopes?

A digital microscope is a modified variant of the typical optical microscope in which The output image is captured by a digital camera and is displayed on a monitor. In a digital microscope, there is no way of viewing the sample through an eyepiece. Most digital microscopes have built-in LED light sources whose intensity can be controlled as per the requirement.

A digital microscopic system is entirely designed based on computer images and does not take human vision properties into consideration. Nowadays, digital microscopic systems are available in the form of simple USB microscopes to complex industrial microscopes. The sample is placed on a microscope slide. The digital microscopic system allows a more detailed analysis of the sample specimen. Some commercial microscopes eliminate the illumination optics such as Phase constant illumination and Köhler illumination.

digital microscope
A digital microscopic system. Image source: Brad Flickinger
An insect observed with a USB microscope
CC BY 2.0

How does a digital microscopy work?

In general digital microscopy, the specimen is first placed on the stage. The specimen is then illuminated depending upon the light requirements. The light rays reflected off the specimen pass through the microscope objective lens for forming an erect real image inside the microscope tube. The point at which the real image is formed is where the CCD (charge-coupled device) is placed. Light rays from this point are processed by the CCD to form a magnified image of the specimen on the monitor screen. If the microscope is using a digital camera instead of a CCD then the point where the intermediate image is formed coincides with the focal point of the camera lens.

The magnification of the image produced by the CCD can be increased by increasing the size of the monitor screen. The width, length, diagonal, and circular measurements of the specimen can be obtained from the screen itself. Some advanced digital microscopes have inbuilt software installed to carry out such measurements. Digital microscopy helps in obtaining very clear and high-resolution images of several types of living and non-living sample specimens.

How to use a digital microscope?

Step 1: Place the sample specimen on the microscope stage.

Step 2: Illuminate the sample with appropriate light intensity and illumination angle.

Step 3: Select the required objective magnification.

Step 4: Use the coarse and fine adjustment focus knobs to bring the specimen sample to proper focus.

Step 5: Observe the image of the specimen on the monitor screen and carry out the required measurements (width, length, diagonal, and circular measurements).

What is the resolution of a digital microscope?

A digital microscope having a typical 2 megapixel CCD generates an image of 1600×1200 pixels. The image resolution in this case depends on the field of view of the camera lens. If we divide the horizontal field of view by 1600, it can give the approximate pixel resolution. Image resolution can be enhanced by generating a sub-pixel image.

The Pixel Shift Method is used for obtaining higher resolution images. In this method, an actuator is used for physically moving the CCD in order to capture multiple overlapping images at one go. These multiple images are combined with the images within the microscope, to obtain sub-pixel resolution images. In this method, sub-pixel information is provided, and the averaging of a standard image is also a known way to obtain sub-pixel information. Certain software is specially designed to enhance the image resolution shown in the monitor.

2D measurement

Generally, digital microscopic systems (including high end digital microscopic systems) tend to measure the given specimen in 2D. These measurements are carried out onscreen by simply measuring the distance from one pixel to another. This is capable of providing width, length, diagonal, circle measurements and more structural information. Some digital microscopic systems are able to count the number of particles also.

3D measurement

Some advanced digital microscopic systems are now capable of providing 3D measurements. This is obtained with the help of image stacking. The microscopic system takes the images of the sample starting from the lowest focal plane in the FOV of the camera lens to the highest focal plane with the help of a step motor. These images are then reconstructed to produce a 3D model based on image contrast to providing a 3D color image of the specimen.

These 3D models can be then used to carry out calculations however, their precision depends on the step motor and depth of field of the camera lens. Digital microscopy is used commonly for several material research purposes like dynamic materials experiments.

What is the difference between a stereo microscope and a digital microscope?

A stereo microscope and a digital microscope mainly differ in terms of magnification. The stereo microscope magnification is given by the product of the objective magnification and the magnification of the given eyepiece lens. Since a digital microscope lacks an eyepiece, the magnification is given by multiplying the objective magnification and the magnification of the given CCD-monitor pair (or electronic magnification). The electronic magnification can be determined by calculating the ratio of the dimension of the image on the monitor to the dimension of the specimen.

In digital microscopy the rays directly fall on the CCD camera. This often helps in producing better resolution images compared to stereo microscopes. In stereo microscopes the human vision properties are taken into consideration unlike digital microscopes.

An USB digital microscope. (types of microscope)Image source:
Rico Shen
2008 Computex – D & i Award: AnMo Dino-Lite Digital Microscope.http://CC BY-SA 4.0view terms File:2008Computex DnI Award AnMo Dino-Lite Digital Microscope.jpg

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About Sanchari Chakraborty

I am an eager learner, currently invested in the field of Applied Optics and Photonics. I am also an active member of SPIE (International society for optics and photonics) and OSI(Optical Society of India). My articles are aimed towards bringing quality science research topics to light in a simple yet informative way. Science has been evolving since time immemorial. So, I try my bit to tap into the evolution and present it to the readers.

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