Lecture 15: Cameras & Lenses (38)
selinafeng

In lecture, Professor Ng said that a very short flash of light in a dark room means that the only light that arrives at the camera comes from that very brief duration when the room is illuminated. Does that mean this effect is not possible in non-dark rooms? How is high speed photography achieved in (for example) super fast wildlife shots?

ZizhengTai

I'm still a little confused why high-speed photography needs long exposure. Looking at the slide on motion blur below, it seems to capture a nonblurry photo of a fast-moving object, we instead need short exposure?

briana-jin-zhang

@ZizhengTai The reason why high speed photography needs long exposure is so that the resulting picture is not too dark. This is because exposure is light over time. You bring up a good point about how it feels like it would be a blurry photo though, that is something I'm curious about too.

briana-jin-zhang

Actually I rewatched lecture and I think the reason why it's not blurry is because there is a flash of light for a very brief period of time. If the light only exists for a brief period of time, then other periods of time will be dark and not recorded by the camera, so it will not be blurry.

seohyunjeon

the source of motion blur is from light from different "times" of a moving object reaching the camera (light from before the bullet hit the apple vs after) due to shutter speed being slower than the subject; since they illuminate the room essentially for an instant, it eliminates the possibility of light from the bullet before hitting the apple/at a different position from existing and being factored into the image. i think fast shutter speed can achieve similar effects as the long exposure+flash of light combo?

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