The Ubiquitous 10X Objective

by Chuck Huck, USA

 
 

    Beginners in both astronomy and microscopy are generally obsessed with magnification. They believe that the higher the magnification, the better. This, as most of us know, is not true.  A neighbor recently purchased a telescope for his grandson through a mail order company, and when he couldn't see anything through it, he called me over. I didn't have to look through it because I knew just by looking at the "instrument" that it was nothing but junk. "I paid $100 for this thing", the neighbor complained, "and I can't see a damn thing." I told him to send it back and ask for his money. "I thought this would be a great thing for the grandchild", he said, "especially since it magnifies 500 times".  (I suggested that a good pair of binoculars would probably be a better gift for the grandson.)

     Of course, the magnification stated on the box is pure fiction! It is the same with some toy microscopes that claim to magnify 1200 times—again, pure fiction. Any child looking through such an instrument will see nothing but haze and will become immediately disappointed—and disinterested in microscopy.

    What is all this leading up to? High magnifications are not the means to an end in microscopy. If I had the choice of only one objective, I would definitely choose the 10X. Anything higher provides a shallower depth of field and smaller area. In the case of viewing pond samples, one really needs fairly decent depth of field. Critters are constantly going in and out of focus. Although it is true that the low power objectives (4X, etc.) provide better depth of field and more viewing area, one simply could not get along with only a 4X lens. Neither could one get along with only a 40X objective—consider the depth of field with this lens! The 10X provides a good "in-between" objective that offers an excellent compromise between the 4X and the 20X or 40X objective. It is the 10X objective that gets more use in my microscopy than any other lens, especially when viewing pond collections.

    Another advantage of the 10X objective is in the use of darkfield or Rheinberg illumination. These types of illumination, especially darkfield, or darkground, are quite useful in examining pond specimens. Many of us do not have a specific darkfield condenser and instead rely on patches placed in the filter holder of the condenser. These provide excellent darkfield in magnifications UP TO 100X (with a 10X ocular). Higher magnifications simply do not work with patch-type darkfield illumination. I use darkfield a lot with pond specimens at magnifications of 4X and mostly 10X.

     The 10X objective is probably the most-used lens on the microscope, providing total mags up to 150 or 160X (with a 15 or 16X ocular). It should be pointed out to beginners that extremely high magnification is not the answer to clarity, sharpness and illumination of a microscopic specimen, especially if depth of field and area are a major consideration.

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Published in the August 2001 edition of Micscape Magazine.

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