An insect observed with a digital microscope.
A digital microscope is a variation of a traditional optical microscope that uses optics and a digital camera to output an image to a monitor, sometimes by means of software running on a computer. A digital microscope often has its own in-built LED
light source, and differs from an optical microscope in that there is
no provision to observe the sample directly through an eyepiece. Since
the image is focused on the digital circuit, the entire system is
designed for the monitor image. The optics for the human eye are
omitted.
Digital microscopes can range from cheap USB digital microscopes
to advanced industrial digital microscopes costing tens of thousands of
dollars. The low price commercial microscopes normally omit the optics
for illumination (for example Köhler illumination and phase contrast illumination) and are more akin to webcams with a macro lens. For information about stereo microscopes with a digital camera in research and development, see optical microscope.
History
An early digital microscope was made by a company in Tokyo, Japan in 1986, which is now known as Hirox Co. LTD.
It included a control box and a lens connected to a computer. The
original connection to the computer was analog through an S-video
connection. Over time that connection was changed to Firewire 800
to handle a large amount of digital information coming from the digital
camera. Around 2005 they introduced advanced all-in-one units that did
not require a computer, but had the monitor and computer built-in. Then
in late 2015 they released a system that once again had the computer
separate, but connected to the computer by USB 3.0, taking advantage of
the speed and longevity of the USB connection. This system also was
much more compacted than previous models with a reduction in the number
of cables and physical size of the unit itself.
A digital microscope allows several students in Laos to examine insect parts. This model cost about USD 150.
The invention of the USB port resulted in a multitude of USB microscopes
ranging in quality and magnification. They continue to fall in price,
especially compared with traditional optical microscopes. They offer
high-resolution images which are normally recorded directly to a
computer, and which also use the computer power for their built-in LED
light source. The resolution is directly related to the number of
megapixels available on a specific model, from 1.3 MP, 2 MP, 5 MP and
upwards.
Stereo and digital microscopes
A primary difference between a stereo microscope and a digital microscope is the magnification.
With a stereo microscope, the magnification is determined by
multiplying the eyepiece magnification times the objective
magnification. Since the digital microscope does not have an eyepiece,
the magnification cannot be found using this method. Instead the
magnification for a digital microscope was originally determined by how
many times larger the sample was reproduced on a 15” monitor. While
monitor sizes have changed, the physical size of the camera chip used
has not. As a result magnification numbers and field of view are still
the same as that original definition, regardless of the size of the
monitor used. The average difference in magnification between an optical
microscope and a digital microscope is about 40%. Thus the
magnification number of a stereomicroscope is usually 40% less than the
magnification number of a digital microscope.
Since the digital microscope has the image projected directly on
to the CCD camera, it is possible to have higher quality recorded images
than with a stereo microscope. With the stereo microscope, the lenses
are made for the optics of the eye. Attaching a CCD camera to a stereo
microscope will result in an image that has compromises made for the
eyepiece. Although the monitor image and recorded image may be of higher
quality with the digital microscope, the application of the microscope
may dictate which microscope is preferred.
Digital eyepiece for microscopes
Digital
eyepiece for microscopes Software contain wide ranges of optional
accessories provides multipurpose such as phase contrast observation,
Bright and dark field observation, microphotography, image processing,
particle size determination in µm, pathological report and patient
manager, microphotograph, recording mobility video, drawing and labeling
etc.
Resolution
With
a typical 2 megapixel CCD, a 1600×1200 pixels image is generated. The
resolution of the image depends on the field of view of the lens used
with the camera. The approximate pixel resolution can be determined by
dividing the horizontal field of view (FOV) by 1600.
Increased resolution can be accomplished by creating a sub-pixel
image. The Pixel Shift Method uses an actuator to physically move the
CCD in order to take multiple overlapping images. By combining the
images within the microscope, sub-pixel resolution can be generated.
This method provides sub-pixel information, averaging a standard image
is also a proven method to provide sub-pixel information.
2D measurement
Most
of the high-end digital microscope systems have the ability to measure
samples in 2D. The measurements are done onscreen by measuring the
distance from pixel to pixel. This allows for length, width, diagonal,
and circle measurements as well as much more. Some systems are even
capable of counting particles.
3D measurement
3D
measurement is achieved with a digital microscope by image stacking.
Using a step motor, the system takes images from the lowest focal plane
in the field of view to the highest focal plane. Then it reconstructs
these images into a 3D model based on contrast to give a 3D color image
of the sample. From these 3D model measurements can be made, but their
accuracy is based on the step motor and depth of field of the lens.
2D and 3D tiling
2D and 3D tiling, also known as stitching or creating a panoramic,
can now be done with the more advanced digital microscope systems. In
2D tiling the image is automatically tiled together seamlessly in
real-time by moving the XY stage. 3D tiling combines the XY stage
movement of 2D tiling with the Z-axis movement of 3D measurement to
create a 3D panoramic.
USB microscopes
A miniature USB microscope
Digital microscopes range from inexpensive units costing from perhaps
US$20, which connect to a computer via USB connector, to units costing
tens of thousands of dollars. These advanced digital microscope systems
usually are self-contained and do not require a computer.
Some of the cheaper microscopes which connect via USB have no stand, or a simple stand with clampable joints. They are essentially very simple webcams
with small lenses and sensors—and can be used to view subjects which
are not very close to the lens— mechanically arranged to allow focus at
very close distances. Magnification is typically claimed to be
user-adjustable from 10× to 200-400×.
Devices which connect to a computer require software to operate.
The basic operation includes viewing the microscope image and recording
"snapshots". More advanced functionality, possible even with simpler
devices, includes recording moving images, time-lapse photography,
measurement, image enhancement, annotation, etc. Many of the simpler
units which connect to a computer use standard operating system
facilities, and do not require device-specific drivers. A consequence of
this is that many different microscope software packages can be used
interchangeably with different microscopes, although such software may
not support features unique to the more advanced devices. Basic
operation may be possible with software included as part of computer operating systems—in Windows XP,
images from microscopes which do not require special drivers can be
viewed and recorded from "Scanners and Cameras" in Control Panel.
The more advanced digital microscope units have stands that hold
the microscope and allow it to be racked up and down, similarly to
standard optical microscopes. Calibrated movement in all three
dimensions are available through the use of a step motor and automaded
stage. The resolution, image quality, and dynamic range vary with price.
Systems with a lower number of pixels have a higher frame rate (30fps
to 100fps) and faster processing. The faster processing can be seen
when using functions like HDR (high dynamic range).
In addition to general-purpose microscopes, instruments specialized for
specific applications are produced. These units can have a
magnification range up to 0-10,000x, are either all-in-one systems
(computer built-in) or connect to a desktop computer. They also differ
from the cheaper USB microscopes in not only the quality of the image,
but also in capability, and the quality of the system's construction
giving these types of systems a longer lifetime.
