Cell Phone Miniscope

1. Turn on the cell phone, and put it in camera mode.
2. Tear off a piece of poster tack about the size of a pea and roll it into a cylinder approximately 1 inch (2 to 3 cm) long.
3. Wrap the poster tack around the circumference of the lens, as shown in the photo below. If it isn’t quite long enough to go all the way around, roll it out more to lengthen it and try again.

   

4. Place the putty-wrapped lens on your fingertip, and bring it toward the camera lens on the back of your phone. You should see a dark circle on the phone’s screen (see left photo below). That circle is the outer edge of the laser pointer’s lens on your finger. Use the circle to center the laser-pointer lens as you bring it even closer to the cell phone (see right photo below). Your goal is to place the laser pointer’s lens directly on top of your cell phone’s lens.

    

5. When the putty-wrapped lens touches your cell phone’s lens, you’ll see a reddish rectangle on your screen. This red color is from the blood in your fingertip! If the laser-pointer lens is off-center, the redness won’t be uniform. Instead, there will be a lighter section somewhere on the screen, as shown in the left photo below. Adjust the position of the laser-pointer lens with your fingertip until the red color is uniform across the screen, as in the right photo below. If it's hard to see a color difference, try switching to video mode with the flash on if this setting is available your camera.

    

Your Miniscope is ready; now find an interesting object to photograph!

Put your cell phone in camera/photo mode and bring it very close to an object you want to photograph (click to enlarge the photo below). If you’re unsure where to start, try fabrics (denim, cotton shirts, synthetic fibers), flowers, insects, electronic screens, and kitchen spices (salt, pepper, sugar, dried herbs). Adjust your distance until the object is in focus, and then take your photo.

Most microscopes have built-in lights to illuminate your view. If your photos aren't bright enough, ask a partner to shine a light on an object you’re photographing. You can also shoot illuminated videos by turning on your camera’s flash.

As you can see, adding a laser-pointer lens dramatically increases the magnification capabilities of a cell-phone camera lens.

Although the exact details vary, most cell-phone cameras share attributes with a familiar vision system: an eye! Your eye contains a lens, and a light-sensitive surface (the retina) records an image of what you see.

In a camera, the light-sensitive surface is an electronic screen called a detector. Adding another lens to the cell phone (here, the small but powerful convex lens found in a laser pointer) magnifies everything that’s close to the phone’s camera, similar to the way a magnifying glass works when you look through it. It’s this magnification that makes your Cell Phone Miniscope so mighty.

To explore the optics of your Cell Phone Miniscope, try reversing the orientation of the laser-pointer lens by flipping it over, so the side that was against the phone is now facing outward. Take another photo of something you photographed earlier. Did flipping the lens change the magnification and/or quality of the photo? Try putting the laser-pointer lens onto the camera lens on the screen side of your cell phone. How do the images compare?

For another optics experiment, try adjusting the zoom on your cell phone’s camera. Does changing the zoom change the magnification and/or the quality of the photo? You can also experiment by switching to video mode. Does this affect the magnification or quality of the images?

To measure your Cell Phone Miniscope’s field of view, zoom out as wide as you can and focus your camera on a metric ruler. How many millimeters fit across the screen? This measurement is the diameter of your field of view. Zoom in halfway. How many millimeters fit across the screen now? Finally, zoom in all the way, and determine the width of your field of view at this setting.

When you know the fields of view for your Cell Phone Miniscope, you can estimate the sizes of the things you see. For example, if your whole screen’s field of view is 4 mm wide, and 8 salt crystals fit across the screen, then the size of a salt crystal can be found by dividing 4 mm by 8 salt crystals, for an estimated size of 0.5 mm/salt crystal (see photo below).

For an engineering challenge, try designing and building a light box to use as a platform for viewing slides with a light source shining from below, similar to the setup of a typical compound light microscope. Some additional supplies that may be helpful include a push-button night light or small flashlight, popsicle sticks, straws, a take-out container with a clear lid, paper, tape, and other materials.

You can also challenge your estimation skills using data gathered from your Cell Phone Miniscope. For example, how many sugar granules cover a piece of sugar-coated candy?

Cell-phone use may be restricted in some school settings. While we believe that use of a cell phone in this Snack is appropriate—especially in classrooms with limited access to microscopes—we encourage teachers to work within their school’s expectations.