Sunday, October 7, 2007

Buying a compound microscope

Do I need one? What kind do I need? What’s the difference among them? How much do they cost? These are all common questions when homeschoolers think about microscopes. The answers depend, of course, on your family’s science enthusiasm and budget. Let’s say you are looking to buy a “good” (ie. high-powered, compound) microscope, then where do you begin?

Check out this link to Home Science Tools to see a list and labeled picture of compound microscope parts.

Of these parts, you will most commonly be choosing from these options:

Eyepiece: the vast majority of microscopes have a 10x eyepiece, with or without a pointer in it. A monocular scope has one eyepiece; a teaching or dual-head scope has two independent eyepieces so a teacher and student (or camera) can both view simultaneously; a binocular scope has two eyepieces for one person to view using both eyes. Each is progressively more expensive, especially binocular microscopes.

Nosepiece with Objective lenses: All scopes will minimally have a triple nosepiece, which has 4x, 10x, and 40x objective lenses that, with a 10x eyepiece, give a total magnification of 40x, 100x, and 400x. A quadruple nosepiece adds an oil immersion lens (100x) that is a nice extra requiring you to keep a small bottle of immersion oil on-hand.

Light source: you have a choice of 4 types of electric light, each progressively more expensive. First is the standard tungsten light, which gets hot over time and dries up your specimen. It’s not as bright as other types, but still works just fine. Fluorescent lighting is cooler and brighter, so this is a nice extra. LED lighting is cool, bright, and takes little power to illuminate and is almost exclusively in cordless microscopes. Halogen is the brightest though it also gets quite hot and is more expensive. It’s best appreciated with a binocular scope.

A word to the wise--check how easily you can get replacement bulbs. Microscopes last a long time, often longer than companies, and you don't want a microscope to be rendered useless because you cannot replace the bulb. See if it has a standard bulb that you can get at a hardware or lighting store.

Stage: A basic microscope has a stage with spring clips to hold slides. If you want to scan over a slide, you need to move the slide around with your fingers, which works fine. A nice extra is a mechanical stage in which the slide is held by an arm and you can move it around more smoothly and precisely using knobs for the X-axis (horizontal movement) and Y-axis (vertical movement.)

Other things you might see: The coarse and fine focus knobs may be separate or, preferably, coaxial (one inside the other.) The diaphragm, which adjusts the amount of light coming up through he stage, may be a multi-holed disc or, preferably, an adjustable iris. These scopes are also parfocal (stays in focus) and parcentered (stays centered) when switching objectives.

I have not found any one place with the best price for all types of microscopes. My 3 top sites are the following:

Home Science Tools This is a homeschooling family company. A comparison chart of their microscopes can be seen here. I had to look in the catalogue I had for shipping; it is $5 plus 5% of order total, so somewhere between $10 and $15.

Bargain Microscopes This is a typical company. All their student scopes can be seen here. Shipping is shown with the product, and runs between $20 to $25.

Great Scopes This is another homeschooling family company. Their chart is here. In the order section at the bottom of the page they list shipping as $10.

Keep in mind that you can buy a mechanical stage for most clip stages from Home Training Tools for $24 + shipping.

Tungsten, Monocular, Basic Stage:

  • Triple nosepiece: See the Kids’ Microscope for $95 at Home Science Tools: (Note: you cannot add a mechanical stage to this model. It has separate focus knobs and a multi-holed diaphragm. It has lesser-quality lenses.) Also consider the $110 model at Bargain Microscopes, with better lenses and adaptable stage.
  • Quadruple nosepiece: See the $174 model at Bargain Microscopes.

Fluorescent, Monocular, Basic Stage

  • Triple nosepiece: See Great Scopes SF3 for $149.
  • Quadruple nosepiece: See Great Scopes SAF4 for $209. If, however, you want a mechanical stage, then see Home Science Tools Home 1000x Microscope for $240.
    As of this writing, you can get a free halogen upgrade at Great Scopes (normally $35.)

Binocular scope

  • You can’t beat Bargain Microscopes $276 model, which includes a mechanical stage, halogen lighting, and magnification up to x1600. It’s certainly the best value if you are an enthusiast and have the budget for it. The only thing this model is missing is coaxial focus knobs, but for that option you would need to buy a $375 scope at Great Scopes or a $399 scope at Home Training Tools.

Note that the only non-cordless LED microscope I could find is the National Optical LED Microscope from Home Science Tools for $220 (triple nosepiece, basic stage, separate focus nobs.)

Accessories: Home Science Tools and Edmund Scientifics sell a la carte accessories.

As an additional note, I want to mention low-powered microscopes. These are not the pocket or kid microscopes, but rather those used for viewing large objects. If you are more interested in viewing highly-magnified large specimens instead of thin, slide-mounted specimens, then consider a low-powered microscope. All 3 sites carry several models, the price mostly dependent upon magnification.

Last update: 29 September 2008

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