Resolution in a digital microscope system can refer to several very different things. This is unfortunate because of the confusion the question of “what is the resolution?” brings.

First to consider: the resolution of the camera itself. This is sometimes expressed as some number of lines, i.e. 800 lines resolution, or given as the number of pixels in the camera array, i.e. 1600×1200. For line resolution the measurement is for the number of black and white line pairs that could be resolved if the central, highest resolution portion of the display were extended across the whole screen.

Pretty esoteric stuff since few people look at vertical black and white lines. The number is, though, a relative indication of how sharp the image will be – the higher the number the sharper the image that the camera is capable of producing. The case with high resolution digital cameras is almost straight forward since here all the pixels count- well most of them do anyway.

A camera with 1600×1200 sensor elements will make an image with 1600×1200 pixels. There is a little fudging because of the way the color is derived (demosaicing), but that is another, also somewhat complicated story. With the pixel shifted image however there is none of the demosaicing and each pixel really sees a red and blue and green signal – almost as if it were a 3 three chip camera.

Now to the microscope resolution part of the question:

Because the microscope has a zoom capability and can magnify an object to different sizes, the resolution will be dependent on both the magnification and the resolving power of the lens. The resolution of lenses is ultimately dependent on the wavelength of light – in air you simply cannot see anything below about half the wavelength of the illuminating light no matter how good the lens is or how much it will magnify.

Without getting too technical, the theoretical limit is about .33 micrometer laterally and about 1 micrometer vertically but the practical limit is usually a little higher, perhaps closer to 1 micrometer in the X/Y and 5 micrometers or more in the Z for lower magnification lenses.

In a perfect world, that would mean you need a minimum magnification of roughly 300x to be able to just resolve two 1-micrometer objects. In practical terms, samples rarely have the extreme contrast or other physical and optical properties necessary to allow that resolution at that magnification.

There is also the distinction that needs to be made between resolving, which is more of a theoretical exercise, and in being able to “see” the resolution. Sampling theory and optical physics define the resolving power of the system but, in practical terms, the magnification needs to be probably three to five times or more higher than theory would predict in order to have enough information in the image to actually “see” the resolution.

Higher magnification is indeed empty magnification but at least you will have the image spread across enough pixels to allow you to visually distinguish between adjacent objects.