Microscope Shopping List

Saturday July 31, 2010

This lab is an introduction to the microscope. We're going to cover how to use a compound microscope, the basics of optics, slide preparation, and why we can see things that are invisible to the naked eye.

What's a compound microscope? Compound microscopes are basically two lenses put together to make things appear larger. If you've ever used magnifying glass, you've noticed how the lens makes words easier to read. If you were to look through two magnifiers (one stacked on top of the other with space in between), you've seen this effect multiply to create an even larger image. That's exactly what a compound microscope does. It uses stacked lenses to greatly increase the magnification.

I'll show you how to get the most out of your investment by learning how to operate a microscope and prepare specimen slides. Click here for a printer-friendly version of this page.

Selecting a Microscope

The first thing you need to do is select a compound microscope. Cheap microscopes are going to frustrate you beyond belief, so we've provided recommendations that will get last your kids through college.

It can be a daunting task to find high quality microscopes and accessories at affordable prices. Here are a couple of recommendations for microscope and equipment that will last your kids through college. You'll also need additional items like slides, coverslips, tweezers, and other basic equipment.

The microscope you select will last a long time. Expect to pay at least $100 for a decent microscope that will provide many years of use. Here are ones we recommend investing in...

Economy Model: The Kids Microscope is a great entry level microscope for under $110. It meets the optical requirements to do our microscope labs but has only single intermediate focusing. It is also available in a cordless LED model that you can use in the field. If your children are young, this may be a good scope to start out with.
Student Model: The Home Microscope is an excellent 5th - 12th grade level microscope with fluorescent lighting that will really meet all the microscope needs of most families. It is well built with very good optics and will stand up to many years of use. I recommend the additional mechanical stage, as stage clips can be frustrating when working at high power!
Advanced Model: There is a Serious Student Model that includes the mechanical stage, iris diaphragm for lighting control, extra 100x oil immersion objective for 1,000x magnification, and immersion oil. This one will take you far in your studies of the micro world. Using the 100x objective with immersion oil is more challenging but also very rewarding as your child is able to see more and develop advanced microscope skills.
All-the-Bells-and-Whistles Model: The Ultimate Home Microscope is really a great microscope (and very similar to the one I personally use with the teaching head attached). This is a university/lab level microscope that is built to withstand the rigors of daily use. This scope is heavier, sturdier, and has all the advanced features like 100x oil immersion objective, iris diaphragm lighting control and a mechanical stage with very easy to use controls. It is also available in a binocular model that is more comfortable to use.When your microscope arrives, keep it in its packaging until you watch the next video. I'll show you how to handle it, store it, and where not to touch.
No matter which microscope you select, you'll want to be sure it meets these criteria: at least three objectives (40X, 100X, 400X) and the optics are all glass to provide better quality images and the microscope frame construction is metal to provide the durability you want. Most microscopes include a dust cover and custom fit styrofoam box for safe storage. Optional additions include a mechanical stage (which we highly recommend), a fourth 100x objective lens (for 1,000x magnification), and adjustable iris diaphragm for better lighting/contrast control.
By the way, if you're considering the the fourth 100x lens, make sure you get the special “oil immersion” objective. Light tends to do weird things when you magnify it that much, and to avoid these kinds of problems, scientists use a drop of oil on the slide to connect the objective with the slide. However, you can't do this trick with just any objective lens - you need to have a special kind of lens that won't get mussed up when contacted with oil (hence the “oil immersion” type).

Where to Find Other Essentials

In addition to a microscope, you'll also need additional items like slides, cover slips, tweezers, and other basic equipment. Here's what you need to complete the labs in this section:

Supplemental Equipment:

These items are not required for this lab, however if your budget allows for these items in the future, they are very nice to have...

Prepared Slide Sets: Using our labs you will learn to make different kinds of microscope slide mounts and examine a variety of samples that you can easily collect. Prepared slides contain specimens that have been professionally stained and prepared so that you can expand your microscope studies to a great variety of plant and animal life that you would otherwise not have access to. The general slide set and the biology slide set are two sets that contain a great variety of specimens to expand your microscopic studies.
Microscope Case: While the dust cover and styrofoam box that come with your microscope provide a good degree of protection, you may want to consider a microscope case to provide greater protection and convenience in carrying and storing your microscope. These cases have the added advantage of also storing your microscope accessories with your microscope in one location.
Digital Microscope: This one is actually cheaper than most optical models listed above, and I've used it when teaching kids. The best part is, all kids can view at the same time, and you can take both pictures and video of your specimens while viewing. It's really a great deal for the price. The one I really like is the Celestron 44340 LCD.

Can’t afford a microscope?

I’ll show you how to build a very simple microscope using two handheld magnifying lenses! All you need is an afternoon, a few kids, and two magnifiers per kid. Now it doesn't come close to any of the microscopes above, but it will allow you to do some basic experimentation. (The magnifiers do not need to be the same magnification.) Gather up a few coins, dead bugs, and plant specimens and you’ll be all set for a microscope adventure.


Microwhat?

Saturday July 31, 2010

Welcome to our unit on microscopes! We’re going to learn how to use our microscope to make things appear larger so we can study them more easily. Think about all the things that are too small to study just with your naked eyeballs: how many can you name?


Let’s start from the inside out – before you haul out your own microscope, we’re going to have a look at what it can do. I’ve already prepared a set of slides for you below.  Take out a sheet of paper and jot down your guesses – here’s how you do it:


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What is it?

Take a peek and see if you can figure out what each one is. Record your guess on a piece of paper. Don’t spend more than 90 seconds on each one. If you’re working with others, have everyone write down their answers individually, and then work together and discuss each one. Come up with a final group conclusion what’s on each slide before peeking at the answers.


plant cells
Paramecium Respiratory Tissue Hair Follicle
Green Algae Water Flea Pine Wood

Need answers? Hover your mouse over each slide to reveal the title.


More questions you can ask:

1. List the ways that microscopes are used. Why bother using them anyway? (Can you name four?)


2. What do you already know about microscopes? List two things.


3. What would you really like to learn about microscopes? Name three, at least.


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Anatomy of the Microscope

Saturday July 31, 2010

Nose? Objective? Stage? What kind of class is this?  Well, some of the names may sound a bit odd, but this video will show you what they are and how they are used. As you watch the video, touch the corresponding part of your microscope to get a feel for how it works.


NOTE: Be very careful NOT to raise the stage too high or you’ll crack the objective lens!  Always leave a space between the stage and the lens!! Anytime you use the coarse adjustment knob, always look at the stage itself, NOT through the eyepiece (for this very reason). When you use the fine adjustment knob, that’s when you look through the eyepiece.




More questions to ask:

1. After you’ve learned the different parts of the microscope, swing around and teach it to a nearby grown-up to test your knowledge. See if you can find all these parts: eyepiece, base (legs), objective lens, eyepiece, diaphragm (or iris), stage, fine and coarse adjustment knobs, mirror/lamp, nose.


2. Show your grown-up which parts never to touch with your fingers.


3. What’s the proper way to use the coarse adjustment knob so you don’t crack the objective lens?


Care and Cleaning

1. Pick up the microscope with two hands. Always grab the arm with one hand and the legs (base) with the other.


2. Don’t touch the lenses with your fingers. The oil on your fingers will smudge and etch the lenses. Use an optical wipe if you must clean the lenses. Steer clear of toilet paper and paper towels – they will scratch your lenses.


3. When you’re done with your scope for the day, reset it so that it’s on the lowest power of magnification and lower the stage to the lowest position. Cover it with your dust cover or place it in its case.


How to Use a Microscope: Optics, Observing, and Drawing Techniques

Saturday July 31, 2010

How do the lenses work to make objects larger? We’re going to take a closer look at optics, magnification, lenses, and how to draw what you see with this lesson. Here’s a video to get you started:




Here’s what you do:


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1. Take a look at the eyepiece of your microscope. Do you see a number followed by an X? That tells you the magnification of your microscope. If it’s a 10X, then it will make objects appear ten times larger than usual.


2. Peek at the objective lenses. They’re on the nose of the microscope, and there’s usually 3 or 4 of them. Do you see the little numbers printed on the side of the lenses, also followed by an X? Find the one that says 4. if you look through just that lens by itself, objects will appear 4 times as large. However, it’s in a microscope, so you’re actually looking through two lenses when you use the microscope. What that means is that you need to multiply this number by the eyepiece magnification (in our example, it’s 4 * 10 = 40) to get the total power of magnification when you use the microscope on this power setting. It’s 40X when you use the 10X eyepiece and 4X objective. So objects are going to appear 40 times larger than in real life.


3. Practice these with your microscope – here are the settings on my microscope – help me fill out the table to figure out how to set the lenses for the different magnification powers:


Eyepiece
Objective
Total Magnification
10X
4X
10X
100X
40X
400X
10X
1000X



Questions to Ask:

1. What does this table above look like for your microscope?


2. Your microscope may have come with an additional eyepiece. If so, add it to your table and figure out the range of magnification you have.


3. What is your highest power of magnification? Set it now.


4. List three possible combination of eyepiece and objective lenses if the power of magnification is 100X.


Learning to Look

Do how do you use this microscope thing, anyway? Here’s how you prepare, look, and adjust so you can get a great view of the micro world:




Download Student Worksheet & Exercises


1. Carefully cut a single letter (like an “a” or “e”) from a printed piece of paper (newspaper works well).


2. Use your tweezers to place the small letter on a slide and place a coverslip over it (be careful with these – they are thin pieces of glass that break easily!) If your letter slides around, add a drop of water and it should stick to the slide.


3. Lower the stage to the lowest setting using the coarse adjustment knob (look at the stage when you do this, not through the eyepiece).


4. Place your slide in the stage clips.


5. Turn the diaphragm to the largest hole setting (open the iris all the way).


6. Move the nose so that the lowest power objective lens is the one you’re using.


7. Bring the stage up halfway and peek through the eyepiece.


8. If you’re using a mirror, rotate the mirror as you look through the eyepiece until you find the brightest spot. You’ll probably only see a fuzzy patch, but you should be able to tell bright from dim at this point.


9. Use the coarse adjust to move the stage slowly up to bring it into rough focus. If you’ve lowered the stage all the way in step 7, you’ll see it pop into focus easily. (Be careful you don’t ram the stage into the lens!)


10. Use the fine adjust to bring it into sharp focus. What do you see?


Drawing What You See

Learning to sketch what you see is important so that the view is useful to more than just you. Here’s the easy way to do it: get a water glass and trace around the rim on a sheet of paper with your pencil. This gives you a nice, large circle that represents your scope’s field of view (what you see when you look into the microscope). Now you’re ready for the next step:




1. Draw a picture of that the letter looks like under the lowest power setting in your first circle and label it ‘right side up’. Then give the slide a half turn and draw another picture in a new circle. Label this one ‘upside-down’.


2. If you’re using a mechanical stage (which we highly recommend), twist one of the knobs so that the slide physically moves to the right as you look from the side (not through the eyepiece) of the microscope. If you’re using stage clips, just nudge the slide to the right with your finger. Now peek through the eyepiece as you move the slide to the right – which way does your letter move?


3. Now do the same for the other direction – make the slide move toward you. Which way does the letter appear to move when you look through the eyepiece?


4. What effect do the two lenses have on the letter image as you move it around? (Need a hint? Look back at the Microscope Optics Lesson from Unit 9)


Look back at your two drawings above. Let’s make them so they are totally useful, the way scientists label their own sketches. We’re going to add a border, title, power of magnification, and more to get you in the habit of labeling correctly. Here’s how you do it:


Border You need to frame the picture so the person looking at it knows where the image starts and ends. Use a water glass to help make a perfect circle every time. When I sketch at the scope, I’ll fill an entire page with circles before I start so I can quickly move from image to image as I switch slides.


Title What IS it? Paramecia, goat boogers, or just a dirty slide? Let everyone (including you!) know what it is by writing exactly what it is. You can use bold lettering or underline to keep it separate from any notes you take nearby.


Magnification Power This is particularly useful for later, if you need to come back and reference the image. You’ll be quickly and easily able to duplicate your own experiment again and again, because you know how it was done.


Proportions This is where you need to draw only what you see. Don’t make the image larger or smaller – just draw exactly what you see. If it’s got three legs and is squished in the upper right corner, then draw that. Most people draw their image smaller than it really is when viewed through the eyepiece. If it helps, mentally divide the circle into four quarters and look at each quarter-circle and make it as close to what you see as you can.


Exercises


  1. Why do we use microscopes?
  2. What’s the highest power of magnification on your microscope? Lowest?
  3. Where are the two places you should NEVER touch on your microscope?
  4. Fill in the blanks with the appropriate word to describe care and cleaning of your microscope:fingers       lowest                                               handsarm                                       toilet paper                                    legs                        dust cover
    1. Pick up the microscope with two ________.  Always grab the _________with one hand and the _______(base) with the other.
    3. Don’t touch the lenses with your _________. The oil will smudge and etch the lenses. Use an optical wipe if you must clean the lenses. Steer clear of ____________ and paper towels – they will scratch your lenses.
    5. When you’re done with your scope for the day, reset it so that it’s on the _________ power of magnification and lower the stage to the lowest position. Cover it with your __________ or place it in its case.
  5.  What things must be present on your drawing so others know what they’re looking at?
  6.  What’s the proper way to use the coarse adjustment knob so you don’t crack the objective lens?
  7.   List three possible combination of eyepiece and objective lenses if the power of magnification is 100X.
  8.  Briefly describe how to dry mount a slide.
  9.  How could you view a copper penny with your microscope?

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Preparing a Dry Mount Slide

Saturday July 31, 2010

Make sure you’ve completed the How to Use a Microscope activity before you start here!


This is simplest form of slide preparation!  All  you need to do is place it on the slide, use a coverslip (and you don’t even have to do that if it’s too bumpy), and take a look through the eyepiece.  No water, stains, or glue required.


You know that this is the mount type you need when your specimen doesn’t require water to live. Good examples of things you can try are cloth fibers (the image here is of cotton thread at 40X magnification), wool, human hair, salt, and sugar. It’s especially fun to mix up salt and sugar first, and then look at it under the scope to see if you can tell the difference.


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Here’s what you do:



1. Pull a hair from your head and lay it on a slide. If it’s super-curly, use a bit of tape at either end, stretching it along the length of the slide. Keep the tape near the ends so it doesn’t come into your field of view when you look through the microscope.


2. Lower the stage to the lowest setting and rotate the nose piece to the lowest magnification power.


3. Place the slide on the stage in your clips.


4. Focus the hair by looking through the eyepiece and slowly turning the coarse adjustment knob. When you’re close to focus, switch to the fine adjustment knob until it pops into sharp view.


5. Open your science notebook and draw a circle. Sketch what you see (don’t forget the title and mag power!)


6. When you’re done, lower the stage all the way and insert a new slide… and repeat. Find at least six things to look at. We’re not only learning how to look and draw, but hammering a habit of how to handle the scope properly, so do as many as you can find.


Don’t forget to check the windowsills for interesting bits. Use baby food jars or film canisters to collect your specimens in and keep them safe until you need them.


TIP: If you want to keep your specimen on the slide for a couple of months, use a drop of super glue and lay a coverslip down on top, pressing gently using a toothpick (not your fingers) to get the air bubbles out. Let dry.


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Preparing a Wet Mount Slide

Saturday July 31, 2010

Make sure you’ve completed the How to Use a Microscope activity before you start here!


Anytime you have a specimen that needs water to live, you’ll need to prepare a wet mount slide. This is especially useful for looking at pond water (or scum), plants, protists (single-cell animals), mold, etc. When you keep your specimen alive in their environment, you not only get to observe it, but also how it eats, lives, breathes, and interacts in its environment.


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The first thing you need to do is collect your pond water. Make sure it has lots of good stuff in it! You’ll need a 20mL sample. Once you have it, place it on a table along with your microscope, slides, cover slips, tweezers, and dropper. If you’re using Protoslo (if critters are too fast, this slow them down for easier viewing), get that out, too. Open up your science notebook, draw a bunch of circles for drawing borders, and then watch this video:



Download Student Worksheet & Exercises


1. Place a slide on the table.


2. Fill the eyedropper with pond water and place a drop on the slide.


3. Place the edge of the cover slip on the pond water drop, holding the other edge up at an angle. Slowly lower the end down so that the drop spreads out. You want a very thin film to lay on the slide without any air bubbles or excess water squirting out. If you go have bubbles, gently press down on the cover slip to squish them out or start over.


4. Take time practicing this – you want the water only under the coverslip. Dab away excess water that’s not under the slide with a paper towel.


5. Lower the stage to the lowest setting and rotate the nose piece to the lowest magnification power.


6. Place the slide on the stage in your clips.


7. Focus by looking through the eyepiece and slowly turning the coarse adjustment knob. When you’re close to focus, switch to the fine adjustment knob until it pops into sharp view.


8. Adjust the light level to get the greatest contrast so you can see better.


9. Move the slide around (this is where a mechanical stage is wonderful to have) until you spot something interesting. Place it in the center of your field of view, and switch magnification power to find a great view (not too close, not to far away). Adjust your focus as needed.


8. Open your science notebook and draw a circle. Sketch what you see (don’t forget the title and mag power!)


9. When you’re done, lower the stage all the way and insert a new slide… and repeat. Find at least six things to look at. We’re not only learning how to look and draw, but hammering a habit of how to handle the scope properly, so do as many as you can find.


NOTE: If the critters you’re looking at move too fast, add a drop of Protoslo to the edge of your slide to slow them down (by numbing them). The Protoslo will work its way under the cover slip.


Exercises


  1. Why do we use a wet mount slide?
  2. Give one example of a specimen that would use a wet mount slide?
  3. How do you prepare a wet mount slide?
  4. Why do we stain specimens?
  5. Give one example of a specimen that would use a stain.
  6. What type of stain can we use (give at least one example).

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Slide Preparation: Staining

Saturday July 31, 2010

Make sure you’ve completed the How to Use a Microscope and also the Wet Mount activities before you start here!


If your critter is hard to see, you can use a dye to bring out the cell structure and make it easier to view.  There are lots of different types of stains, depending on what you’re looking at.


The procedure is simple, although kids will probably stain not only their specimens, but the table and their fingers, too.  Protect your surfaces with a plastic tablecloth and use gloves if you want to.


We’re going to use an iodine stain, which is used in chemistry as an indicator (it turns dark blue) for starch. This makes iodine a good choice when looking at plants. You can also use Lugol’s Stain, which also reacts with starch and will turn your specimen black to make the cell nuclei visible. Methylene blue is a good choice for looking at animal cells, blood, and tissues.


In addition to your specimen, you’ll need to get out your slides, microscope, cover slips, eye dropper, tweezers, iodine (you can use regular, non-clear iodine from the drug store), and a scrap of onion. If you can find an elodea leaf, add it to your pile (check with your local garden store). Here’s what you do:


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Download Student Worksheet & Exercises


1. Fill a container with water and add a small piece of elodea leaf and onion. You’ll want the onion to be a thin slice, no more than a quarter of an inch thick.


2. Practice making a wet mount first.  Put a fresh slide on the table. Using tweezers, pull off a thin layer of onion (use a layer from the middle, not the top) and place it on your slide. Gently stretch out the wrinkles (use a toothpick or tweezers) and add a small drop of water and cover with a cover slip. Take a peek at what your specimen looks like on low power – do  you notice it’s hard to see much?  Draw what you see in your notebook.


3. Now increase the power and look again.  Draw a new sketch in your notebook.


4. Now we’re going to highlight the cell structure using iodine.  Lugol’s is also iodine, but the regular brown stuff from the drug store works, too. Grab a bottle of the one you’re going to use.


5. To stain the specimen, we’re going to add the stain to one side of the cover slip and wick away the water from the other side. Use a folded piece of tissue paper and touch it lightly to one side of the cover slip as you add a single drop of stain to the other side. When the stain has flowed through the entire specimen, take a peek and draw what you see in a a fresh circle.


6. Do the same thing with the elodea leaf. And anything else plant-based from your backyard. Or refrigerator.  Draw what you see and don’t forget to label it with a title and power of magnification!


Exercises


  1. Why do we use a wet mount slide?
  2. Give one example of a specimen that would use a wet mount slide?
  3. How do you prepare a wet mount slide?
  4. Why do we stain specimens?
  5. Give one example of a specimen that would use a stain.
  6. What type of stain can we use (give at least one example).

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Slide Preparation: Heat Fixes

Saturday July 31, 2010

Make sure you’ve completed the How to Use a Microscope and also the Wet Mount and Staining activities before you start here!


If you tried looking at animal cells already, you know that they wiggle and squirm all over the place. And if you tried looking when using the staining technique, you know it only makes things worse.


The heat fix technique is the one you want to use to nail your specimen to the slide and also stain it to bring out the cell structure and nuclei. This is the way scientists can look at things like bacteria.


You’re going to need your microscope, slides, cover slips, eyedropper, toothpicks or tweezers, candle and matches (with adult help), stain (you can use regular iodine or Lugol’s Stain), sugar, yeast, and a container to mix your specimen in. Here’s what you do:


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Download Student Worksheet & Exercises


1. Fill your container with warm water.  Add about a tablespoon of yeast (one packet is enough) along with a teaspoon of sugar.  The warm water activates the yeast and the sugar feeds it.  You should see a foam top form in about 10 minutes.


2. Using your eyedropper, grab a bit of your sample (you want the liquid, not the foam) and place a drop on a fresh slide. Spread the drop out with a toothpick.  You want to smear it into a thin layer.


3. Light the candle (with adult help). Heat the slide in the flame by gently waving it back and forth. Don’t stop it in the flame, or you’ll get black soot on the underside of the slide and possibly crack it because the glass heats up and expands too fast. You also don’t want to cook the yeast, as it will destroy what you want to look at. Just wave it around to evaporate the water.


4. Add a drop of iodine (or stain) to the slide. Wait 15 seconds.


5. Rinse it under water. (You can optionally stain it again if you find it’s particularly difficult to see your specimen, but make sure to look at it first before repeat staining.)


6. Place a drop of water (use a clean eyedropper) on the specimen and add the cover slip.


7. Lower the stage to the lowest setting and rotate the nose piece to the lowest magnification power.


8. Place the slide on the stage in your clips.


9. Focus by looking through the eyepiece and slowly turning the coarse adjustment knob. When you’re close to focus, switch to the fine adjustment knob until it pops into sharp view.


10. Adjust the light level to get the greatest contrast so you can see better.


11. Move the slide around (this is where a mechanical stage is wonderful to have) until you spot something interesting. Place it in the center of your field of view, and switch magnification power to find a great view (not too close, not to far away). Adjust your focus as needed.


12. Open your science notebook and draw a circle. Sketch what you see (don’t forget the title and mag power!)


NOTE: What other things can you look at?  You can scrape the inside of your cheek with a toothpick and smear it on a fresh slide, take a mold sample from last week’s leftovers in the fridge, or…? Have fun!


Exercises


  1. Why do we use heat fixes?
  2. Briefly describe how to do a heat fix.
  3. What is a specimen that needs a heat fix?

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Microscopes and Telescopes

Wednesday February 3, 2010

Hans Lippershey was the first to peek through his invention of the refractor telescope in 1608, followed closely by Galileo (although Galileo used his telescope for astronomy and Lippershey’s was used for military purposes).  Their telescopes used both convex and concave lenses.

A few years later, Kepler swung into the field and added his own ideas: he used two convex lenses (just like the ones in a hand-held magnifier), and his design the one we still use today. We're going to make a simple microscope and telescope using two lenses, the same way Kepler did.  Only our lenses today are much better quality than the ones he had back then!

You can tell a convex from a concave lens by running your fingers gently over the surface – do you feel a “bump” in the middle of your hand magnifying lens?  You can also gently lay the edge of a business card (which is very straight and softer than a ruler) on the lens to see how it doesn't lay flat against the lens.

Your magnifier has a convex lens – meaning the glass (or plastic) is thicker in the center than around the edges.  The image here shows how a convex lens can turn light to a new direction using refraction. You can read more about refraction here.

A microscope is very similar to the refractor telescope with one simple difference – where you place the focus point.  Instead of bombarding you with words, let’s make a microscope right now so you can see for yourself how it all works together. Are you ready?

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How to Make a Microscope

Materials:

  • 2 hand held magnifiers
  • dollar bill
  • penny - Note: The penny used in this video shows the Lincoln Memorial, which was shown on pennies minted between 1959 - 2008.

Here's what you do: Hold one magnifying glass in each hand.  Focus one lens on a printed letter or small object.  Add the second lens above the first, so you can see through both.  Move the lens toward and away from you until you bring the letter into clear focus again.   You just made a microscope!  The lens closest to your eye is the EYEpiece.  The lens closest to the object is the OBJECTive. The image here is of the objective part of a compound microscope.  The different silver tubes have different sizes of lenses, each with a different magnification, so the same scope can go from 40X to 1,000X with the flip of a lens.

How do I determine magnification power for my microscope? Simply multiply the powers of your optics together to get the power of magnification. If you’re using one lens at 10X and the other at 4X, then the combined effect is 40X. You’ll usually find the power rating stamped in tiny writing along the magnifier.

So now you've made a microscope.  How about a telescope? Is it really a lot different?

The answer is no.  Simply hold your two lenses as you would for a microscope, but focus on a far-away object like a tree.  You just made a simple telescope… but the image is upside-down!

microscope1We don’t fully understand why, but every time we teach this class, kids inevitably start catching things on fire.  We think it’s because they want to see if they really can do it – and sure enough, they find out that they can!  Just do it in a safe spot (like a leaf on concrete) if that’s something you want to do. Click here for a detailed instructional video on how to do this safely.

How do I connect the flaming shrubbery back to the main optics lesson? Ask your child why the leaf catches on fire… and when the shrug, you can lead them around to a discussion about focus points of a lens.  It’s hard for kids to visualize the light lines through a lens, so you can shine a strong light through a fine-tooth comb as shown in the image above.  Use clear gelatin (or Jell-O) shapes as your “lenses” and shine your rays of light through it.  If your room is dark enough, you’ll get the image shown above.

The point where all the lines intersect is where things catch fire, as the energy is most concentrated at this point. Note how the lines flip after the focus point – this is why the telescope images are inverted.  The microscope image is not flipped because you’ve placed the image (and/or your eye) before the focus point.  Play around with it and find out where the focus point is.  Slide your lenses along a yardstick to easily measure distances.

How to Make a Telescope

Materials:

  • 2 hand held magnifiers
  • window

Want to experiment further? Then click for the Optical Bench experiment and also sneak a peek at the Advanced Telescope Building experiment where you will learn about lenses, refractor, and newtonian telescopes.

Ready to buy your own professional-quality instrument that will last you all the way through college? Click here for our recommendations on microscopes, telescopes, and binoculars.
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Laser Microscope

Wednesday February 3, 2010

Did you know that you can use a laser to see tiny paramecia in pond water? We’re going to build a simple laser microscope that will shine through a single drop of water and project shadows on a wall or ceiling for us to study.


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Here’s how it works: by shining a laser though a drop of water, we can see the shadows of objects inside the water. It’s like playing shadow puppets, only we’re using a highly concentrated laser beam instead of a flashlight.


If you’re wondering how a narrow laser beam spreads out to cover a wall, it has to do with the shape of the water droplet. Water has surface tension, which makes the water want to curl into a ball shape. But because water’s heavy, the ball stretches a little. This makes the water a tear-drop shape, which makes it act like a convex lens, which magnifies the light and spreads it out:


Here’s how to make your own laser microscope:


Materials:


  • red or green laser (watch video for laser tips)
  • large paperclip
  • rubber band
  • stack of books
  • white wall
  • pond water sample (or make your own from a cup of water with dead grass that’s been sitting for a week on the windowsill)


Download Student Worksheet & Exercises


Exercises


  1. Does this work with other clear liquids?
  2.   What kind of lens occurs if you change the amount of surface tension by using soapy water instead?
  3.   Does the temperature of the water matter? What about a piece of ice?
  4.  Does this work with a flashlight instead of a laser?
  5.  Do lasers hurt your eyes? How?

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