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03-25-2007, 06:51 AM
I put a box on my head recently and was intrigued when I saw a small hole in the corner would project an image on the opposite side of the box. It was if the hole was smaller, it would be like a wide angle lens and if it were bigger it would be telephoto. Also, if it were smaller it would be sharper and more focused (but of course a lot darker).
Light's always going in all direction and only with the box on my head I can filter out everything exept for what I saw?
03-25-2007, 06:58 AM
Did you ever make a pinhole camera in school? I did, but I don't remember any of the science behind it.
03-25-2007, 07:29 AM
LOL!
OK, I'm laughing... I've got a little pinhole project of my own right now. Maybe I'll share a bit more in a few days. Rather odd, the timing of this post. ;)
03-25-2007, 10:59 AM
Yup, that's pretty much exactly it! With a lens, glass elements gather the light from various (although obviously fairly close) angles from an object in the scene and focus them onto an imaging plane.Originally Posted by OcularLimpidity
With a pinhole (which is effectively what you've got) all but a very few beams of light from each object can get through to the imaging plane, causing the scene to focus and an image to be projected. That's why the smaller the hole is the sharper the image is. Smaller hole = less bright, deeper (and in the case of a pinhole better) focus. Larger hole = more light, shallower (or likewise, worse) focus. Just like a lens!
03-25-2007, 11:14 AM
Wikipedia has a good in depth explanation:
http://en.wikipedia.org/wiki/Pinhole_camera
Blurring is either due to bigger 'circles of confusion' with larger holes and greater pinhole to image plane distance, or diffraction effects with very small pinholes. Pinhole cameras effectively have infinite depth of field as light isn't bent by a lens. They are also 180 degrees angle of view, but the actual useable image angle of view is limited by vignetting by the thickness of the sides of hole the material is punched in. Light rays coming at angles other than 90 degrees to the hole are increasingly shaded by the edges of the hole.
03-25-2007, 12:39 PM
Aren't you talking about "camera obscura" ?
03-25-2007, 04:46 PM
Yes, pretty much... A camera obscura is a version which you stand inside - so in this case may be a more accurate desciption - whilst a pinhole camera refers to a device which produces a fixed image, usually on photographic paper.
The concept and physics are identical, however.
Btw, thanks for the much better explanation ericyoung, I tried to simplify it in my post and ended up disclosing far less information in a far more confusing fashion!!!
03-25-2007, 06:34 PM
I've heard of someone making a pinhole camera in winter, placing a single drop of water in the pinhole, wait for it to freeze, and use it like a lens.
According to the legend, the image is RIDICULOUSLY sharp.
I should call mythbusters....
03-25-2007, 08:51 PM
Hmmm... Doubtful. I might try it though. Our cold weather is gone, but I've got extra room in the freezer. I don't see how it would work given that water expands and traps air as it freezes, more so in a slower freeze than a fast one. Also tends to crystalize unless flash-frozen. I suppose I could dial-down the freezer and place the pinhole camera in there for a few hours. Open up the freezer and apply a very tiny drop of water to the pinhole and hope it freezes quick. Then I would have to load it with film and try to take a picture right there before anything melts.
Call me crazy, but I seriously may try it. :nerd:
03-25-2007, 10:08 PM
The idea is that it will create a meniscus lens. Two potential "mythbusting" comments here:
1) I'm with Jeff - just don't think it will work in practice (but still have a go mate, I'm intrigued to see what happens!).
2) Meniscus lenses aren't actually all that great, and whilst the small "stop" will help with sharpness I don't think you're likely to get an image sharper than a good lens on a good camera. But hey, what do I know?!!
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