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User Guide - Foldscope Mini

Foldscope Mini - paper microscope

Welcome to Foldscope Mini’s online user guide! Use the links listed below to jump to a specific section on this page.


Your Foldscope Mini Explorer Kit includes the following items:

Foldscope Mini Explorer Kit Contents

Mini Front and Back

Key Metrics

The Foldscope Mini Explorer is a microscope with the following metrics:

  • Magnification: 140X

  • Resolution: ~2 microns

  • Back focal length: ~0.5 mm

  • Depth of field: ~0.01 mm

  • Field of view: ~0.5 mm (diagonal radius)

The Foldscope Mini is composed of paper components and a lens.

  • The paper components are composed of a synthetic material, which is waterproof, tear-resistant, and inexpensive.

  • The lens is a borosilicate glass ball embedded in a circular black plastic piece.

Microscopy 101

  • A microscope consists of three essential components: a sample, a lens, and a light source. The sample, or specimen, is what you're looking at in your microscope. The lens is what magnifies the sample-it makes it look larger by bending the light you see.

  • Resolution is a measure of how clearly you can see things in a microscope. The resolution of a lens is the size of the smallest feature you can distinguish when looking through it. Foldscope Mini’s resolution is 2 microns, which is about the length of an E. coli bacterium. One micron is 0.0001 cm. 

  • Most microscopes you might use in a classroom or laboratory are compound light microscopes. This means that their lenses are made of multiple pieces of curved glass, each piece similar to an eyeglass lens. In the Foldscope Mini, our lens is a single glass ball. This is the same type of lens used in the very first microscope made by Antony van Leeuwenhoek in the 1600s!

  • In a Foldscope Mini, as in most microscopes, it’s easiest to view a sample when it’s mounted on a slide, a flat rectangle that holds your specimen. Slides provide a stiff base for the sample and keep it secure for viewing. Slides are traditionally made of glass, but Foldscope Minis can also be used with slides made of paper.

  • A light source is important for illuminating the sample. In transmissive light microscopy, the light shines through the sample. This is the type of microscopy that Foldscope Minis use: the sample is in between the light source and the lens. Transmissive light microscopy is very effective for viewing samples that are thin and translucent, as the sample is only visible if it allows light through to the lens.

  • Every microscope has a set focal length: the distance at which something viewed through the lens looks clear and crisp, not blurry. In a standard 140X Foldscope Mini lens, the back focal length is 0.56 millimeters, about the thickness of 5 sheets of paper. This means that a Foldscope Mini sample must be only 0.56 millimeters away from the lens to be viewed clearly-- so close it’s almost touching! This flatness is one reason Jim and Manu thought that paper would be a good material for building a microscope with this lens. When you focus a microscope, you move the sample farther or nearer to the lens until it is the right distance away. A sample that is out of focus will appear blurry.

  • Depth of field is the thickness of your sample that appears in focus at the focal length. When you adjust the focus, the depth of field is like a three-dimensional window that moves forward and backward through the sample, and everything within the window’s thickness appears clear. Foldscope Mini’s depth of field is 13.6 microns, which is 0.0136 millimeters.

  • Think about making a circle with your hand and looking through it with one eye-- you will only be able to see a small circle, but moving your head will let you see different things in that circle! This circle is called your field of view. Just like looking through your curled hand, all microscopes have a limited field of view: the lens allows you to see only a small area of any sample at one time. Moving your field of view is called panning. For a microscope, that means moving the sample relative to the lens, placing different areas of the sample beneath the lens.

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Viewing Methods

The Foldscope Mini is viewed directly with the eye. See a video tutorial of how to use the Foldscope Mini.

Eye Viewing

To view a sample directly with your eye, hold the Foldscope Mini with the logo side facing you (the wrong side will have a do-not-view-from-this-side icon) and bring the lens up to the eye.

  1. While you view, point the back of the Foldscope Mini toward a light source, such as a lamp or clear sky (but do not look directly towards the sun!)

  2. To focus, use your thumbs  to move the lens closer/farther from the sample. Press thumbs to bring the lens closer to the sample. release to go farther.

Moving & Focusing

Moving your slide with the Mini

To move, align your index fingers with the opposite edges of your slide. Use the combined pressure to move the slide slightly up and down or side to side.

  • This motion will move the sample, allowing you to explore different areas.

  • You should see the objects in your field of view move as you move your sample.

To focus, squeeze the Foldscope Mini or slightly bend it.

  • This motion will move the lens further/closer to your sample, allowing you to adjust focus.

  • You should see the objects in your field of view shift from blurry to crisp as you squeeze or bend.

Samples & Slides

Foldscope MiniSample Insertion

To use your Foldscope Mini, you need to insert a sample so that there’s something to see! It’s easiest to view samples mounted on either a glass, paper or our card slide. To learn more about collecting and preparing samples, see the sample preparation section. Foldscope Minis can also be used with prepared slides, such as the ones sold in these kits or in our card sets.

  1. To insert a sample, open the Foldscope Mini in the shape of a V
  2. Hold your slide vertically
  3. Slides are inserted in a black slot on the inner part of the Foldscope Mini.


  • Before viewing any sample, you should first align it with the lens. With the Foldscope Mini open, shift the slide until the portion of the slide containing your sample is directly in line with the back of the lens. Although you can still pan around to view different areas while viewing, it helps to begin in a region of interest.

Sample Preparation

Sample collection tips

  • A good Foldscope Mini sample is anything you’re curious about! Although some things are easier to see than others, it’s possible to mount just about anything with a few useful tricks.

  • Because the Foldscope Mini is a transmissive light microscope, it’s important that your sample is translucent enough to allow light to pass through.

  • Examples of common items that might be interesting to examine in your Foldscope Mini include hair, fabric/fibers, mold, fruit skin, leaves, flower petals, printed paper, insects, algae/moss, pond scum, pollen, feathers.

  • Finding a sample:

    • The most important first step is finding a good source of samples. For pond samples, for instance, the grosser and gunkier, the better! Standing water is better than running water, and somewhere with more vegetation is better than somewhere clear and open. Look for ponds, marshes, and puddles with lots of algae and decaying plant matter.

  • Collecting a sample:

    • Using an Eppendorf tube, or any small bottle or jar, scrape along a particularly gunky section of your water source. Once it’s full, hold it still and take a good look-- if your water has lots of life, you may be able to see microorganisms swimming around after the debris settles. You can also grab pieces of algae or seaweed with a pair of tweezers.

  • Preparing your sample:

    • If your sample is particularly dense, it can be helpful to spread it out in a tray before selecting a droplet to place on your slide. If you dump your collection tube into the upturned lid of your well plate or another small container with a smooth, clear base, and then place it over a white piece of paper, it may be easier to find specimens of interest. You can also use tweezers to break up any plant material.

    • Mount your sample onto a slide, and insert it into your Foldscope Mini

  • Viewing your sample:

    • After your sample is securely mounted, it can be viewed as any other slide: make sure that your coverslip is closer to the lens, insert it in the slide stage, align your point of interest with the center of the lens, face a light source, and view with your eye.

Slide mounting tips

The easiest way to get a good image is to mount your sample on a slide. Blank card slides are provided with your kit and you can also purchase glass slides.

To mount a sample on a card slide, first place a clear sticker (included in every kit, extras available here) or a piece of translucent tape over the window, then place your sample on the sticky side of the tape. If your sample is something that’s already relatively flat and attaches securely to the tape, then there’s no need to cover it-you’ll get a better image by viewing your sample directly. This technique works well with samples such as paper, leaves, flower petals, feathers, and hair or other fibers. If you have a more fragile sample such as mold or pollen, you can cover it with a second clear sticker, sandwiching the sample in the middle of the window. 

To mount a sample on a glass slide, simply place your sample on the slide and cover it with a clear cover sticker, a piece of transparent tape, or a glass coverslip

Direct sample viewing (without a slide)

  • If you want to view something without using a slide, such as a leaf or a piece of paper, you can try placing it directly between the slide stage and back flap.

  • Try viewing a leaf that is still attached to a tree or other plant! This would be very difficult to do with a conventional microscope, but Foldscope Mini's portability means that you can observe living systems in action.

Ring stickers

  • If your sample is particularly thick or large, our accessory ring stickers can be used as a spacer. This is especially important for samples you don’t want to squish, such as insects or other fragile specimens whose 3D structure you want to preserve. You can use either the white ring stickers included in every kit, in which case you’ll need to use a clear sticker or glass coverslip on top, or you can use our black ring stickers, which are specially designed for sample mounting. These ring stickers come in varying thicknesses suitable for a range of samples and include their own transparent plastic coverslip, with no adhesive layer to distort imaging.

  • If you’re using a card slide, first stick a clear sticker or a piece of transparent tape over one of the windows, then stick a ring sticker in the center of that window on the sticky side of your tape. If you’re using a glass slide, just stick the ring sticker in the middle of your slide. Remove the ring sticker’s top cover, then place your sample in the center of the ring sticker, and seal it with a cover slip as usual. If one ring sticker is not sufficient, you can stack multiple ring stickers on top of each other until it’s high enough for your sample.

Water samples

  • Watch a video tutorial of how to create wet mount slides for water samples. Live water samples are one of the coolest things you can look at through the Foldscope Mini! But they also can be a bit tricky to prepare. Creating these slides can take some patience and practice, so don’t be frustrated if it takes you a few tries to get it right.

  • Wet samples are much easier to mount on glass slides, but it is also possible to use paper slides.

    • If you’re using a card slide, first stick a clear cover sticker or a piece of transparent tape over one of the windows, then stick a ring sticker in the center of that window on the sticky side of your tape.

    • If you’re using a glass slide, just stick the ring sticker in the middle of your slide.

    • Either way, the ring sticker creates a well that holds in the water and provides a spacer so the organisms don’t get squished. Use a dropper to select a small drop of water.

    • If your organisms are visible to the naked eye, it’s worth trying to chase them down!

    • You can also use tweezers to take a pinch of algae or other plant matter from your sample and then place it in the center of the ring-- microorganisms are often nestled in vegetation. It’s important not to take too much plant matter, and to spread it out with your tweezers in the ring; thick clumps will be very dark, dense, and hard to see through.

    • If you can see the water surface bulging above the top of the ring sticker, you need to remove some water so that your cover slip will lay flat without too much spilling. You can do this by sucking some of the liquid back up with the dropper, by using the dropper to knock some water out across the ring sticker and drying the excess with a paper towel, or by dipping the corner of a paper towel directly into your well of water and pulling it away immediately as soon as some liquid is absorbed.

    • Once the water is at an appropriate level, seal your well by placing a glass cover slip, a clear cover sticker, or a piece of transparent tape over the ring sticker. To minimize bubbles, start placing your cover from one side of the ring and slowly tilt it down until it is flat across the sample.

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Card Slides


Your Foldscope Mini Explorer kit includes two Card Slides that can be used to create a new slide to practice your viewing, focusing, and panning skills.

Inserting the Card Slide

Insert the card slide into the Foldscope Mini with the frontside facing the lens, short side down.

Once inserted, the back side of the slide should be visible facing outward.

Viewing the Card Slide

The card slide is viewed similarly to a paper or glass slide and is focused on and moved in the same way.

Troubleshooting FAQ

This FAQ section covers how to use Foldscope Mini. For other questions, visit our FAQ page or Company page.

Why can’t I see anything?

  • Correct side - Are you looking into the Foldscope Mini correctly? Holding the sides between with your thumbs and index fingers, bring the front side up to your face and look into the lens with one eye. Your eye should be quite close to the lens aperture, which is the small hole in the middle of the lens.

  • Assembly check - The first step is to make sure your Foldscope Mini is assembled properly. Check your work by following along with our assembly video.

  • Slide insertion - Did you insert a slide? If you didn’t put in something to look at, there won’t be anything to see. More information on slide preparation and insertion is above.

  • Sample aligned with lens - Is your sample aligned with the lens? If your sample is very small, you might not see it because it’s outside your Foldscope Mini’s field of view. Open your Foldscope Mini and see where your sample is on the slide. Shift the slide so that your sample is directly over the back of the lens, and then close the back flap and try looking again.

  • Light source - Are you facing a light source? You won’t be able to see anything if your sample isn’t properly illuminated. To view a sample clearly, there must be light coming in through the aperture on the back. Make sure that you are facing something bright, such as the sky, a lamp, or a window (but not directly at the sun!).

  • Sample quality - If you inserted a large sample that’s over the lens and are facing a light source but still can’t see anything clearly, your sample might be too thick. Try slicing it, squishing it, or spreading it out so that it is translucent enough to let light through, or try using a brighter light source.

Why is my sample blurry?

  • Focus - Almost every time you view a sample in a microscope, it will be blurry when you first look at it. This is because you need to bring it into focus by moving the sample closer to or further from the lens. With Foldscope Mini, you do this by squeezing or bending the Mini. If your image is blurry, first try adjusting the focus and see if that makes it clear.

  • Sample towards the lens - If you’ve tried the full range of focus and your image is still blurry, make sure your slide is inserted so that the sample is as close as possible to the lens. In glass slides, this means that the side with the coverslip should be facing the lens, and the smooth glass side should be facing out. In paper slides, if you’re using only one piece of plastic tape, the sticky side with your sample should be facing the lens and the smooth tape side should be facing out. If your sample is sandwiched between two pieces of tape, however, there’s nothing special about either side so direction doesn’t matter.

  • Lens - Make sure that your lens is clean and properly attached. Before viewing your first sample, we recommend that you clean your lens by rubbing each side of the glass ball for 10 seconds with the pointed cotton swab we provide. Try to avoid touching the glass surface of the lens with your fingertips, as our skin has oil that will smudge it.

  • Lighting - A good light source can make a huge difference in the quality of your image. Make sure that you are pointing your Foldscope towards a bright, evenly illuminated area, such as the sky, a well-lit wall, or a window. If your image seems unclear, try shifting your angle towards the light or use a different light source. Although any bright light source should work.

Why can’t I see all of my sample at once?

  • Microscopes have a limited field of view-- the area that you see has a limited size. This means that you can only see the part of the sample within that area.

Yay, I have it working! What are some cool things I can do with my Foldscope Mini?

  • Congratulations! Go out and explore-- we encourage you to be curious and investigate the world around you, whatever that might be. Check out our community website microcosmos.foldscope.com to get inspiration from the discoveries of other users around the world.

I’m still struggling… is there any way I can get some assistance here?

  • If you need extra help getting your Foldscope Mini to work or want someone to show you more advanced techniques, send us an email at info@foldscope.com

How much does Foldscope Mini magnify the sample?

What are the differences between a Foldscope Mini and a conventional microscope?

  • Conventional microscopes typically have better optical performance and greater stability and control. Conventional microscopes are also often expensive. Foldscope Minis are smaller, lighter, less expensive, and more durable. This portability makes it ideal for field research, hiking trips, and other rugged scenarios. It is also ideal for under-resourced settings where people would not otherwise have access to a microscope. Although the low price is also an appeal for classroom use, Foldscope Mini’s main benefit is that it allows every student to have their own microscope, providing more hands-on microscopy time and opening new possibilities for independent research projects as students can take their Foldscope Minis home with them. Foldscope is not trying to replace conventional light microscopes. We still believe that it is important for students to learn traditional lab microscopy techniques when possible.

What have people used Foldscope for?

  • Foldscope has been used for a wide variety of projects all over the world. Check out the research page for a list of papers that reference Foldscope, or explore our Microcosmos community site to see what people are discovering every day.

How hard is it to build a Foldscope Mini?

  • Building a Foldscope Mini for the first time typically takes around 5 minutes, but once you know how it can easily be assembled in less than 1 minute. Your Foldscope stays assembled after you build it, so you only have to put it together once. Follow along with our assembly tutorial video

What age is a Foldscope Mini suitable for?

  • We recommend Foldscope Mini for explorers ages 8 and up.

What kinds of things can you look at with a Foldscope Mini?

  • Just about anything you can put on a slide! More information on sample collection can be found in the Samples & Slides section.

Do all samples have to be mounted on glass slides?

  • Foldscope Minis works best with samples that are mounted on slides or our cards, but this includes more than you might think. Check out the Samples & Slides for more information on what you can view and how to view it.

Additional questions should be directed toinfo@foldscope.com.