Veho Deluxe USB Powered Microscope
I just bought this microscope and after some initial disappointment, because I didn't really know how to use it and the documentation that comes with it is almost useless, I am now quite pleased with it. There is some confusion in reviews here over what this microscope can do -- is it really a 400x power microscope? The advertising describes it as "Magnification: 20x - 400x (Plus digital zoom in 640x480 mode)" Does that mean it can continuously zoom for 20X to 400x? The manual that comes with it does not really tell you how to use it. So I did a little experimentation, and found that it really has two fixed magnifications, appx. 20x and appx. 400x.
There is a cylindrical drum you can twist for focusing the microscope. As you turn it an internal lens moves up and down the barrel, changing the distance to the specimen. On the drum, there's a scale, with markings from 20 to 400 on it, that is quite misleading -- it suggests that you can optically zoom continuously from 20x to through 400x. But that is not the case. Instead, there are two fixed magnification levels, one nominally 20x and one about 400x, corresponding to two different focus locations, and they do not correspond to the locations on the scale you would expect!
Using it at 20x power:
If you place a specimen, like a piece of paper, directly under the microscope and place the clear plastic end of the microscope directly on the paper, the 20x focus occurs when you turn the drum beyond the top of the scale, past the 400, then a little past the 20 mark as the scale starts repeating. At this focal point the internal lens is moved up the tube, far from the specimen. The field of view is 13.5 mm. You can then move the microscope farther from the paper, readjusting the focus as necessary. You can even move the microscope quite far from the specimen, and still be able to focus it with 20x magnification. When it is focused at infinity, (at the extreme end of the scale, about 60 over the top), the field of view is 11.2 degrees, or about 3" wide when the subject is 12" from the end of the microscope.
Using it at 400x power:
To get the the 400x magnification, again place the clear plastic end of the microscope directly on the specimen, say a dollar bill. The 400x focus location occurs when the drum is rotated beyond the bottom of the scale, to the 400 below the 20 mark. At this point, the internal lens is moved down the tube, to nearly as close to the specimen as it can get (about 22mm). The field of view is only about 0.8 mm, or 2 degrees. Most users would never notice that the microscope can focus at the 400x magnification: to attain it you must move the focus lens to nearly the full bottom of its travel; it is easy to go through the focal region too quickly to see it; and the documentation makes no mention of it. People may think the higher magnification is obtained by zooming in digitally on your computer screen, without realizing that the microscope focuses with high magnification itself. You'll need to turn on the LED illumination for the 400x scale to get an image. (There are eight white LEDs that provide good even illumination, not four as advertised.)
Zooming:
As well as these two focus regimes, there is a software zoom option. If you choose a capture size of 640x480 you can go to the preferences menu and choose zoom to zoom in digitally. The field of view zooms from 13.5mm down to 4.2 mm.
Measuring actual magnification:
The 20x and 400x are only approximage values, but you can measure the actual magnification by viewing a millimeter ruler or finer reticule if you have one. If the image capture size is set to 1280x960, I find that the width of the field of view is 13.5 mm at the "20x" focus, and about 0.8 mm at the "400x" focus. (about a 17x difference) The resolution, that is, the size of a single pixel in the field of view, is 13.5mm/1280= 10.5 microns for the "20x" focus, and 0.8mm/1280=0.6 micron for the "400x" focus. (Of course, the optics aren't perfect, and it appears to me that at the "400x" focus the optical resolution is about 3 pixels, that is, the smallest features you can see are about 2 micron in size. The magnification you see on your computer screen depends on the screen pixel size, also called the pixel pitch. Mine is 0.282 mm (or 90 pixels per inch, most LCD screens are 90-100 pixels/in.). For my screen, the two actual magnifications are then, 1280*0.282mm/13.5mm = 26.7x and 1280*.282mm/0.8mm = 451x. This is for viewing on the computer screen at "actual size", not zooming in.
Measuring object sizes:
The software allows you to measure objects with rulers you can draw over a picture, but you need to enter the actual magnification to calibrate the software ruler. They suggest you take that reading from the scale on the microscope, but there's so much up and down play in the focus drum that you can't rely on its readings for the true magnification. It's best to calibrate the field of view by taking a picture of a millimeter ruler. Then you know what true size the full width of the captured image corresponds to. That works well for the appx. 20x focus point. Unfortunately, the magnification box allows entry of only integers up to 220, so you can't enter an actual magnification, like 451, to get accurate numbers.
Even so, you can measure object sizes and do the math yourself. In particular, you can use the software ruler to measure sizes in pixels with a magnification factor of one, and get an accurate pixel measurement.
Saving images:
The software lets you save the images in uncompressed *.bmp or compressed *.jpg file formats. You can choose the level of compression for the *.jpg files; remarkably, the 3.7 MB files (1280x960x3bytes) can be compressed to about 100KB without much loss of resolution.
Image resolution:
Despite the ad hype, the sensor is not a 2 megapixel (Mp) sensor -- the spec sheet in the instruction manual says it is 1.3 (Mp). The maximum resolution is attained when you choose an image size of 1280x960 = 1.23 Mp. Although there is an option for capturing images at 1600x1200, those images are interpolated, and don't result in any greater actual resolution.
With these considerations in mind, you'll find that this microscope is a great value for the money, and you can take some really good photomicrographs with it.
