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The Optics of Cameras

The Optics of Cameras. Joe Two Bear Jason Waskiewicz. Elements of Photography. F-stop: size of aperture (hole) the light comes through Focal Length: distance at which light is focused ISO: ability of the camera to collect light (not part of lab)

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The Optics of Cameras

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  1. The Optics of Cameras Joe Two Bear Jason Waskiewicz

  2. Elements of Photography • F-stop: size of aperture (hole) the light comes through • Focal Length: distance at which light is focused • ISO: ability of the camera to collect light (not part of lab) • Speed: how quickly a picture is taken (slower lets in more light)

  3. General Camera Parts Mirror Eyepiece Opening Shutter Lens(es)

  4. Activity 1 – F-stop • F-stop controls how big the opening is that lets in light • F-stop numbers are backward: small numbers mean a big opening, big numbers mean a small opening

  5. How an Opening Works • Early camera: pinhole camera • Light reflects off an object in all directions • Pinhole selects only a tiny amount of the reflection • Result is a sharp image These light rays never enter the pinhole.

  6. Try it out! Viewer • Work through Activity 1 • Demonstration of Scattering • Pinhole Viewer (shown here) Parchment Paper Pinhole

  7. Sample Results I was able to see even the base of the bulb! This was a very difficult photograph to take; it actually looks better through the box.

  8. F-Stop Post-Discussion Adjustable Opening

  9. Effects of Opening Size Small Opening Large Opening

  10. Small F-stop (Large Opening) Boy stands out because he is in focus • Large opening (small f-stop) creates blurry background • Light comes in at all angles • Only small part of image comes in with correct focus • Great for portraits • Also useful for low-light photography People in the background are out of focus

  11. Low-light Photography • This is not in the student version, but this is an example of a picture taken in extremely low light, but it looks good because I had the lens wide-open!

  12. Large F-stop (Small Opening) • Small opening (large F-stop) makes the image sharper throughout • Fewer light rays come in to distort focus • More of the image is sharp • Great for landscapes • Not useful in low-light photography (without a tripod) Buttes in the distance are sharp Abandoned farmhouse is also sharp

  13. Activity 2 – Focal Length • Many cameras have zoom lenses (like the far right) which have adjustable focal length • Focal length measures the distance at which the image of an object comes into focus • Different lenses have different focal lengths and uses

  14. Comparing Focal Lengths 18mm lens good for wide angle (like a building – abandoned farmhouse earlier) 50mm lens like the human eye views the object

  15. Comparing Continued 85mm has slight magnification, good for portraits (picture of the boy earlier) 55-250mm zoom lens at 250mm zoom

  16. Start Activity 2 • First do the Estimation • Then do the Measuring the Focal Length • Illustrated to the right • Note how the image projects on the screen • Also note that the LENS moves, there is some distortion in this picture

  17. First Activity • The only difficulty I had with this one was that you need to project the image straight on. Don’t try to project an image that is at an angle.

  18. The Two Sample Graphs – Actual Results from Bowman!

  19. Focal Length Discussion • Focal length is the distance from the lens at which parallel light rays entering the lens focus on a single point • When you project the sun with a magnifying glass, you are applying the focal length!

  20. Real LensesCount them: 9 actual lenses in the lens Lens(es)

  21. Activity 3 – The Telescope • Actual camera lenses consist of several lenses put together • All 3 lenses here are “telephoto” lenses • None of these are the actual length of the focal length because of how several lenses interact.

  22. The Telescope • Activity 3 puts 2 lenses together as a telescope • Illustration shows (roughly) the setup for a telescope.

  23. View Students Will See Through the Telescope Without Telescope With Telescope: and what a tough photograph to take!

  24. Final Discussion • Even most of the less expensive cameras allow adjustment of speed, ISO, f-stop, and focal length • With a little knowledge, you can take much better pictures • Experiment, try out the features of your camera: digital makes it cheap • Photography is fun, and most of us own at least a basic camera

  25. UND is awesome

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