Monthly Archives: December 2009

Information About Microscopes for Home Use

A friend who is a parent recently asked me for advice on how to pick a good microscope for use at home for his children. (I think some lucky kids might be getting an interesting Christmas present this year) 🙂 I thought I’d publish my thoughts here so that more parents might benefit. I’m not going to endorse any specific brand or reseller but instead will try to give you some information that will help you make informed choices if you are also in the market for an educational microscope.

First a disclaimer. I’m not a biologist or a biology teacher and so I don’t have years of experience first hand with microscopes. I have however had a few years of experience in the Educational supply industry and am aware of some of the issues you will run into when you are in the market for a microscope. Anyone with more experience should feel free to comment, make recommendations, or point out any issues I might have left out.

Buying a good microscope can be a dizzying proposition if you’d like to get it right. There are many manufacturers, resellers, types, and a huge price range from simple magnifiers all the way up to thousand dollar lab equipment. Microscopes and Magnifiers generally fall into price ranges including “Toy”, “Economy”, “Educational/School”, and “Industrial/Scientific”. In general you don’t want to waste your time or money on “Toy” Microscopes.

Types of Microscopes and their intended uses:

Magnifiers

  • Purpose: Simple magnification
  • Great For: Young kids to explore more details of the world around them.
  • Neat things to look at: The back of a U.S. penny to see that Lincoln is sitting inside the Lincoln memorial, fabrics and threads, insects, textures on objects, wood grain.
  • Magnification 5-30X
  • Best Kind: Those mounted in frames used in the textiles industry for thread counting
  • Worst Kind: Cheap Dime Store/Toy/Kids magnifiers
  • Notes: Best to get some kind of frame and built-in light source (LED if possible). It is ok and even preferable to get a magnifying glass made out of acrylic plastic. If you can check the lens for distortions, light halos, or other aberrations.

Field/Pocket Microscopes

  • Purpose: Higher magnification than a simple magnifying glass sometimes with features of an actual microscope but intended to be portable.
  • Great For: Use outside or on a trip.
  • Neat things to look at: Grains of sand or soil, insects, parts of plants, the surface of rocks and minerals.
  • Magnification 5-150X (sometimes up to 300 in professional models)
  • Best Kind: Those with higher quality optics, focus adjustments, and built in light sources (single hand-held and sometimes with a clip-on-frame for holding actual slides)
  • Worst Kind: Units without a focus adjustment (toys or units that are really just magnifiers)
  • Notes: If you have a child between the ages of 5 and 10, and don’t care to focus on very small objects (like cells, protozoa, etc) then a good pocket scope is an excellent and inexpensive choice to get a young mind thinking about the structure of the world around them. Some models do even have enough magnification to view large cells and structures in plants. If you have an older child or want to focus on very small objects a more traditional bench microscope (digital or optical) is probably a better choice.

Optical Microscopes

  • Purpose: Viewing details of biological specimens, cells, and other very small objects.
  • Great For: Science Fair experiments in biology, observing different kinds of cells, learning about biological concepts.
  • Neat to look at: Prepared microscope slides, your own slides, cells.
  • Magnification: 30-300X
  • Best Kind: All metal construction with glass optics and built in light source (preferably LED since an LED doesn’t heat the sample as much as quartz or other high power white lights).
  • Worst Kind: Plastic construction with plastic optics or mirror light source. The higher the magnification being used the more problems you will have focusing on a sample if the focus mechanism, stage, or light source is not sturdy and adjustable.
  • Notes: Bench-top optical microscopes (just like the ones you used in Biology class in high school) are great for observing cells and other small objects. Keep in mind if you buy a microscope you’ll also want to have something to look at. The younger your child is the more important having a source of prepared slides can be. Many microscope kits include slides, slide preparation equipment, and pre-mounted slides of common biological specimens. Quality varies directly with price and if you go for a cheap scope you will also probably get cheap slide materials. Glass slides are better though might be dangerous for younger children. Never let your young child use this equipment without supervision. There are also great sources of prepared slides for use with any microscope. An excellent supplier is Carolina Biological Supply Company of Burlington NC.

Optical Stereo Microscopes

  • Purpose: Viewing details on larger objects, especially rocks and minerals.
  • Great For: More detailed viewing of rocks and minerals than can be achieved with a pocket or field scope, though not as good for tiny biological application due to the lower magnification involved.
  • Neat to look at: Rocks and Minerals, Insects, other larger small objects
  • Magnification: 10X to 100X
  • Best Kind: Same rules as an optical microscope, all metal construction, fine focus control, good light source.
  • Worst Kind: Plastic construction, plastic optics, indirect light sources.
  • Notes: If your child has more interest in geology than biology then a stereo microscope may be a better choice since they can focus more on rocks and minerals. Stereo means two eye-pieces and thus the ability to have some depth perception (distorted through magnification) and so is better for seeing structures in 3D.

Hand Held Digital Microscopes

  • Purpose: Viewing small details on objects like rocks and minerals, wood, circuit boards, etc. Similar to a field/pocket magnifier but tethered via USB cable to a computer and therefore able to view the image on a larger screen as well as to take digital images.
  • Great For: Seeing details on the surface of objects that are otherwise too big to bring to a standard microscope. For example you can view the hair on someone’s head or details of the skin on their arm.
  • Neat to look at: The surface of larger objects that can not be moved to the stage of a conventional microscope. Rocks, Minerals, Insects, Human Beings, Electronics, other small objects.
  • Magnification: 5-300X (though usually more like a field scope limited around 100X)
  • Best Kind: Units that have a stage as well as a portable capability.
  • Worst Kind: Models that aren’t much more than a low quality web camera with snap on optics. Always look for the highest resolution digital camera on board as possible.
  • Notes: A USB Digital microscope is probably the best compromise between all features of all the different kinds of microscopes. Since it is connected to a computer you have a large screen to view things on and share with the whole family as well as the ability to take digital pictures and use them in lab reports or science fair experiments. The best kind are those that have high magnification and also have a snap-on stage for use with slides as more of a conventional microscope. Something to consider when looking at digital microscopes is the quality and features of the software that is bundled with the hardware. Look for online reviews for the specific unit you are interested in and let that help you make your decisions.

Optical/Digital Microscopes

  • Purpose: The same as a conventional optical microscope only with a digital camera built in.
  • Great For: All of the same things as an optical microscope but with the added benefits of a digital microscope.
  • Neat to look at: Same as an optical microscope.
  • Magnification: Same as an optical microscope.
  • Best Kind: A quality optical microscope that has a digital camera replacement for the eye piece. Look for all metal construction, glass optics, LED light source.
  • Worst Kind: Plastic construction.
  • Notes: An Optical/Digital Microscope is best for a “lab” or “classroom” type environment with the added benefits of a digital camera and computer-screen display. It has the same limitations as a traditional optical microscope but is slightly better for use with slides and traditional biological applications (like viewing cells).

My personal recommendation is to pick between a hand-held digital microscope with good resolution and a high magnification rate and an optical/digital microscope. The key difference is general magnification vs. biological application though the hand-held unit that has a stage attachment can be used for biological applications too. Overall always look for quality construction, glass optics, metal stage, and direct LED lighting. Don’t forget that prepared slides (especially for biological application) can be an important add-on, as well as slide preparing tools. Generally glass slides are better though you won’t want to pick glass slides with younger experimenters. Always teach your children proper care, use, and safety when using any scientific or technical instrument and always supervise younger children.

Advertisements

Identify It! answer for 12-08-2009

Another round of great guesses. The answer to this Identify It! Challenge is:

Identify It! for 12-08-2009

Identify It! for 12-08-2009

These items are Nuvistors. Nuvistors are the smallest mass produced vacuum tubes and were invented and produced by RCA for use mostly in consumer electronics. Nuvistor is a play on words including “Nu” which sounds like “new” and vistor which sounds like the end of transistor. “Nu” is also similar to “Mu” which is a symbol which stands for the amplification factor of a vacuum tube.

Unlike most vacuum tubes Nuvistors are enclosed inside a metal shell that both provides structure and shields the elements inside the tubes from radio frequency interference. Being metal they are a little more rugged than glass tubes, although unlike transistors they are prone to problems due to vibration. Nuvistors are unique in their manufacture in that instead of each tube being evacuated of air individually and then sealed, entire sets of tubes were placed into a large vacuum chamber, the air removed from the chamber, and then each tube sealed roboticly before all tubes were removed from the chamber. Being small reduced weight and due to the physical smallness of the elements within the tube (cathodes, grids, plates) Nuvisors worked well with high frequency (such as VHF and UHF frequencies used in television transmission.)

Like all tubes, Nuvistors contained a heater, cathode, at least one grid, and a plate. The heater was a wire made of tungsten which is not unlike a filament in a light bulb. Electricity passing through the filament to glow and produce heat. This heat is transferred to the cathode a metal sleave that is wrapped around the filament (but not electrically connected to it). The Edison Effect (noted by Thomas Edison) is that any metal heated in a vacuum will release a charge of electrons into space. When the heater heats the cathode it produces electrons (which can be replenished by supplying the cathode with a fresh supply of electrons by electrically connecting it to a negative voltage supply). As the electrons are emitted from the cathode they can be attracted to another cylindrical conductor known as a plate if it is charged to a positive potential. The plate is connected to a positive voltage source which attracts the electrons from the cathode. Between the cathode and plate are one or more “grids” which are screens of wire. The grid can be connected electrically to an outside voltage source. If the grid is at a potential that is more positive than the cathode but less positive than the plate then electrons can be made to flow to the plate. Since electrons are repelled by negative charges if the grid is connected to a potential that is more negative than the cathode then electrons will be repelled and will not reach the plate. Thus a vacuum tube can act as an amplifier since a small signal applied to the grid can control a larger voltage flowing from cathode to plate.

In the late 1950’s and early 1960’s transistors existed and were being used in electronic devices, however they were not as reliable at high frequencies and were more expensive to produce. Vacuum tubes were still less expensive for a time due to the mass production facilities that already existed for their manufacture.

In our picture we show a 2CW4 and a 6CW4. Both are triodes. The first number indicated the filament voltage, one being 2.1 volts and the other 6 volts. The 4 indicated four elements inside the tube, a filament, cathode, grid, and plate. These tubes are triodes and were used as part of the tuner circuit of early color television sets.

To learn more please visit these pages:

http://www.thevalvepage.com/valvetek/Nuvistor/nuvistor.htm

A reproduction of an article from “Practical Television” magazine from December 1962. This article has a great diagram showing the construction of Nuvistors as well as example circuits that used them.

http://nuvistor.org/1630.htm

An article with some excellent pictures of “Acorn Tubes”… a style of vacuum tube that were the smallest tubes before the production of the Nuvistor. Also some interesting links to some reproductions of 1960’s era electronics magazines relating to amateur radio and “high frequencies”

http://en.wikipedia.org/wiki/Nuvistor

Wikipedia entry on Nuvistors which includes a useful list of part numbers and types.

(insert standard disclaimer on wikipedia article accuracy and non-primary-ness here)

Identify It! Challenge for 12-08-2009

Here is our latest Identify It! Challenge image:

Identify It! 12-08-2009

Identify It! 12-08-2009

The dime is for scale only.  Make your guesses at the Harris Educational Fan Page (http://www.facebook.com/HarrisEducational)

Check back in a few days for the answer.