How to Use a Carousel Projector to Digitize Slides
By Steve Lander
Transparency slides used to be a popular archival medium. They are small, stable and hold a great deal of image data, with some slides able to hold the equivalent of 87 megapixels of resolution. If you need to digitize many 35mm transparency slides for business purposes, it's best to send them to a service bureau that has special high-resolution scanning equipment. However, if you do not need to capture every last bit of detail from your slides, you can also digitize them with a screen, a carousel projector, a tripod and a digital camera.
Make the room in which you will be projecting as dark as possible. If possible, use a room without windows where you can turn the light off. The less light that leaks into the room, the crisper your images will be. If you cannot see your camera to change its settings, either turn the lights on while you are setting it or use a flashlight.
Project a slide. If possible, use an image that has a broad range of brightness, including both very light and very dark areas. Images with a number of vertical lines, like shots of skyscrapers, make it very easy to ensure that everything is lined up correctly.
Line up your carousel projector so that the image is as square to the screen as possible. Hold a yardstick up to what you know to be a straight line. If the line always touches the yardstick, the projector is square; if it slants away from the yardstick, adjust the angle at which the projector sits. This reduces the amount of distortion in the images you capture. It's better to make the image a little bit too small rather than a little bit too large, because it concentrates the light from the projector and lets you use a faster shutter speed.
Position your camera on the tripod so that the image fills its viewfinder screen without being cut off. Look carefully at the edges of the screen to make sure that they perfectly line up. As with your projector, adjust your camera so that it shoots as square to the screen as possible.
Set your camera's ISO speed to its lowest setting. While this necessitates a longer exposure time, it reduces the amount of noise that the camera generates and gives you a more attractive capture.
Take a test picture and look at the image. You might need to reposition your camera slightly because camera viewfinders do not always perfectly reflect their actual capture area.
Set your camera's white balance to "incandescent" or "tungsten." This ensures that the colors that it captures are what you see on the screen.
Set your camera's exposure so that the image is captured with appropriate brightness and contrast. If you are using an image with a broad range of brightness levels, your camera's histogram display should extend to fill as much of the graph as possible without creating a large hump on the right side. Write down the camera's ISO, aperture and shutter speed.
Place your camera in its manual mode. Set the aperture and shutter speed to the values that you just wrote down.
Take a picture of each slide as you project it. To prevent your camera from shaking, use a remote control or, if you do not have one, use its self-timer mode so that it waits a few seconds after you press the shutter to take the image.
Items you will need
A DSLR usually does a better job of capturing images than a point-and-shoot camera.
Steve Lander has been a writer since 1996, with experience in the fields of financial services, real estate and technology. His work has appeared in trade publications such as the "Minnesota Real Estate Journal" and "Minnesota Multi-Housing Association Advocate." Lander holds a Bachelor of Arts in political science from Columbia University.