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Choosing a portable USB microscope
Published:2014-04-03 19:42:07    Text Size:【BIG】【MEDIUM】【SMALL

Being of magnification less than 480X and equipped with reflected illumination, we classify handheld portable USB microscopes into stereomicroscopes according to the principle of optical imaging and features of special structure.

Principle of optical imaging: The objective plane and the image plane (the surface of sensor chip) are of conjugation relationship to the lens between them. One set of objective lens offers two magnifications, low magnification: M1, high magnification M2. M1 X M2 = 1

 

Features of structure: The objective plane and the image plane are fixed, and by moving the lens, you can get the two magnifications at two particular positions, so the focusing wheel also acts as the function of zoom adjuster.


Factors we must take into consideration when choosing a USB microscope:

A. Magnifications: 

Like a normal microscope, the total magnification of a USB portable microscope comes from multiplication of objective magnification and equivalent eyepiece magnification (the sensor chip takes the place where a normal optical microscope eyepiece located, we call the rate of display dot pitch in compare with sensor pixel size as the digital magnification)

Optical magnification: The maximal optical magnification is limited by the minimal working distance, and the minimal working distance is limited by the reflective illuminator. Its hard to guide light to its target field, when the lens is very close to the target.

In this case, the optical magnification must be less than 8X. If we take into consideration of the chip size and the objective field range, and insure that all of the pixels of the sensor are full of light and low magnification, we must limit the magnification less than 4X.

Digital magnification: digital magnification comes from the rate of the display dot pitch in comparison to the  sensor pixel size. The pixel size is 0.0028mm for a 1.3MP and 2.0MP CMOS color sensor, and normally the screen dot pitch we set for a comfortable view is about 0.270mm, so the digital magnification is 96.4X.

Thus, the maximal magnification is 4 X 96.4 = 385.6X.

We conclude that the magnification depends on pixel size, chip size and reflective illuminator located, and we also realize that there is no 500X or 1000X portable USB microscope equipped with 1.3MP or 2.0MP sensor at all.


B. Design of zoom and focusing adjuster:

By turning the adjuster to move the lens to two particular positions, you get the two magnifications (zoom), and by focusing (turning adjuster finely) you can get a clear image. Future Optics patent big wheel adjuster, equipped with built-in dual-guide rail, is worth to be commended.

  


C. Resolution and view field:

High resolution pictures are always welcome, but to capture high resolution images, this needs support of a high quality illumination. The frame rate related with a high resolution image is very low, so we must keep balance with other factors in our selection.

An image with resolution of 1280*1024 captured by our MDA1300 is enough for full screen view on most laptops, and the frame rate of 17 fps is not bad for tracking a movable target in YUY2 format color space.

MDA2000 has a bigger view field in comparison with MDA1300, and a 1600*1200 image is more suitable for full screen view to a 25” PC for designing and QC.

5.0MP USB portable equipped with 5.0MP sensor is not suitable for use in normal condition, 2fps is too low, and ring LED lamp is not enough.

0.3MP USB portable offers a window of 640*480 in screen, and the small size chip can capture a small area of the view field in compare with 1.3MP microscope.

The interpolated resolution is no use for widening the target field to be viewed.


D. Dynamic range and background noise:

Dynamic range and background noise are closely related with the quality of the sensor chip and design of the imaging module. Testing and comparing pictures sent by supplies is worth doing.

    

                     Our MDA1300                                                                               Other product


E. True color:

True color images depend on a high quality sensor, advanced imaging module design project, color temperature range of an LED lamp and software function settings (in color space, image format, video format and extra color compensation).

    

                     Our MDA1300                                                                               Other product

    

                     Our MDA1300                                                                               Other product


F. Picture resolution, preview image resolution and video recording resolution:

By checking video resolution, users can find the real resolution of the sensor and evaluate the function of the  software in "image capture". 0.3MP image can be interpolated into 1.3MP images, but a 0.3MP video cannot be interpolated into 1.3MP video.



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