How to Buy a Microscope

Submitted by Lois Salaun on Tue, 01/29/2013 - 13:33

By Lois Salaun

It is highly recommended that all Koi hobbyists purchase their own microscope. A good microscope is an invaluable tool to help us diagnose parasites on our fish and is money well spent. This brief article will explain the basics of a scope and the minimum needed to view parasites on our Koi. Keep in mind that each added feature will increase the cost. The object is to buy a good quality scope for a reasonable price that will get the job done.

Thanks to Great Scopes for the picture.

First off, buy a sturdy, metal scope with metal parts. Pass on the plastic toy or children’s models. The lenses or optics (objectives) are the most important and most costly part of a scope. A quality scope will have optics (lenses) that conform to the DIN standard for threading and length. Lenses with this standard are interchangeable between scopes. In addition, the lenses should be glass, not plastic and be listed as being achromatic, another industry standard. By spending slightly more up front and staying with industry standards, you will find it easier to locate replacement parts when needed in the future.

Things to consider about the eyepiece(s): we don’t spend hours looking into a scope, so if you don’t mind squinting, then get a monocular eyepiece. If you can’t wink or squint, then pay a little extra for binocular (two eyepieces). I find it easy to focus with one eye, but it’s a personal preference.  An eyepiece that swivels or rotates is a nice convenience. This makes it easy for two people to sit side by side and share. Also, look for one that has a pointer in it.

What about objectives (lenses)? A basic scope has three lenses of different magnifications. These are fixed on the nose piece or head which allows the user to rotate the lenses. For our purposes, lenses of 4x, 10x and 40x are adequate to find the smallest parasites. Combined with the eyepiece of 10x this will give you magnification of 40, 100 and 400 times. More expensive scopes will have a fourth objective of 100x which is an oil immersion lens and in my opinion, really more than we need.

You will need a light source. Older style scopes relied on a mirror to reflect outdoor light. Fortunately, good scopes come with an internal light source – battery powered, electric or both. Batteries need to be charged or replaced. I have always been able to find an electric outlet near the pond to plug in a scope. More important is the type of light. You'll find one of four different types of lighting. The tungsten light bulb is the least expensive. It generates heat and can cook your sample if you leave it on too long. Fluorescent lights are available, don’t generate heat, are cheaper to use, but cost a little more. LED and Halogen lights are the most expensive. Fluorescent is nice, but if you are trying to save pennies, the tungsten is fine. Make sure you buy an extra bulb or that the bulb has a standard base and can be purchased elsewhere.

Adjusting the amount of light or brightness is a consideration. This is done with a diaphragm – either a disk or iris. The disk is the cheapest and is mounted beneath the stage. It usually has six holes in it, each one progressively larger which allows more light. An iris diaphragm is constructed with several flaps in a circle (like a camera lens) that can be adjusted with a simple lever to an infinite number of settings. Again, if trying to save pennies, the disk diaphragm is adequate.

A mechanical stage is a nice convenience and highly recommended. The slide - with your sample - is locked into the mechanical stage under the lenses. It has two knobs, one of which moves the slide from left to right. The other knob moves the slide forward and back. This makes it easy to scan the entire slide quickly and efficiently. Without this feature, you must move the slide by hand under the lens.

Now we need to focus on focusing. A good scope will have both a course and a fine focus with metal gears. Make sure your scope has a “slip clutch” or stop. A microscope with a slip clutch will allow the focus knob to turn in place without damaging the scope's focus gear system. The stop prevents the lens from crashing onto the slide on the stage and damaging the lens.

A simple filter holder is built into some microscopes for color filters. Filters can be useful in providing enhanced contrast and light color correction, and can be a simple substitute for staining, which would kill live specimens. You have to buy different color filters. It’s a nice feature, but not necessary.

A few final comments…If you follow the above guidelines, your scope should be more than adequate for the Koi hobby. Some folks recommend getting the 100x lens which will give a magnification of 1000x with a 10x eyepiece. This is an oil immersion lens. I don’t have this lens and haven’t missed it, but it is useful for examining culture samples. Some microscopes do not support 1000x magnification. If you think you might want to add it later, buy a scope with the fourth location in the head that will accommodate it. Confirm that the condenser will work with a 100x lens.
If you will be traveling a lot with your scope, buy a case for it. If you don’t purchase a case, at least buy a plastic cover to keep it clean. Don’t forget to buy slides and cover slips. I recommend glass cover slips for the least distortion, but they break easily. Use plastic cover slips when working with children.

There are many additional options available to fancy up your microscope. You can buy a camera attachment to take pictures or videos of your slide samples. These can be uploaded to a computer, and in some cases, the slides can be viewed on your computer screen. If you think you might want these features later, just make sure the scope you buy will accommodate them.


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