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Magnification
There is a bit of misunderstanding about magnification factors and zoom systems on microscopes and how they function. Part of the problem has been the creative marketing on the part of some microscope resellers.
Let's set the story straight. The maximum magnification you can get on a standard light microscope is about 1250x to 1600x. This is viewing through the eyepiece with the naked eye which will also give you the finest detail you can see. This detail is termed resolution.
Though we can get large magnification with optical arrangements, digital video, and manipulating a camera up and down over the video coupling lens (the lens that connects the microscope to the camera and focuses the image to the camera chip), what we want is "useful" magnification, not "empty" magnification. Useful magnification is a function of resolution. Resolution is the limit up to which two small objects are still seen separately. It is used as a measure of the resolving power of a microscope.
Resolution in a microscope is a function of the numerical aperture of the objective (printed as NA on the objective). Digging into the mathematics, the maximum resolved distance is equal to the wavelength of the color of light through the specimen divided by 2NA. Going further, the maximum magnification possible with optimum resolution tops out at slightly less than 1000 times the NA. A 100x oil objective typically can have a numerical aperture of 1.3. so 1.3 X 1000 = 1300 as the theoretical limit of magnification with the most resolution. Since no manufacturer makes a 13x eyepiece (13x eyepiece X 100x objective = 1300 mag) we are left with the standard 12.5x eyepieces which gives 1250x magnification.
When a microscope is sold based on some ultimate magnification factor like 8,000x or 30,000x, this is simply related to the physical image size that appears on the video monitor. For example, a red blood cell is 7 to 8 microns in diameter. If you have a red blood cell that is 1 inch large on the video monitor, divide 8 microns into 1 inch (.0254 meters) and you will arrive at the number 3175. So a 1 inch red blood cell on the video monitor is magnified 3175x. Do you have any more resolution of that image than what you can see through the eyepiece at 1250x? No you do not. You just have a bigger image. But sometimes, bigger is better and in the case of microscopy viewing, it is a nice advantage.
Zoom Systems
One way to get a zoom function is through a digital zoom capability either through the camera itself if this is available (hard to find today and on some models not easy to get to through an on screen menu), or through computer graphics if you are putting the image through a computer. Digital electronic zooms are not dependent on a scopes maximum light intensity as it interpolates what it sees and digitally makes the image larger. The problem with this is it has a tendency to give a fractal (jagged) edge around the zoomed objects. (When you are seeking more magnification using higher power objectives, optical zoom systems, or vertical camera adjustments which is explained below, more light is generally required to push the image through the optics. This is not a problem with a Biomedx system 150 watt quartz halogen light source which is standard on all of our scopes.)
A second zoom method is sometimes accomplished through vertically adjusting the camera over the video coupling lens. Ideally, for optimum focus, this should be set at one specific distance. However, if you observe the principles of light and image projection, you will note that the further away you get from the place where you may be projecting an image to, the larger the image gets. By varying a camera's distance over the projection lens (the video coupler) of a microscope, you can obtain a zoom type effect. It is not the best way to accomplish the job, but it is simple and inexpensive. Some companies have patented motorized drives that make the vertical camera adjustment by simply pushing a button. Because of these patents, they ask for a $20-30K premium for their systems. For the level and type of zoom these arrangements offer, this premium is quite excessive. Also, this type of zoom only works when the scope is fitted with finite corrected optics. This type of optic is common on many general microscope systems but the state of the art today is infinity corrected optics which is standard on all Biomedx microscopes.
A third way to get a zoom function is with an optical zoom. This is the best. Magnifying the image not with electronics, nor manipulating the camera distance from the video coupler, but by using optical lenses.
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