Naked Science Forum
Non Life Sciences => Technology => Topic started by: Kudo on 24/11/2010 12:03:24
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Hello everyone, hope you can help.
I remember as a child seeing reflections on the wall from outside. Only a pin hole in the wall with a full image on the opposite wall inside. What is this called, how is it done and could I accomplish this in a basement showing a full image of what is outside projected onto a wall in the basement? Would this be a periscope of some kind, use of mirrors or a prism? [O8)]
[MOD EDIT - PLEASE PHRASE YOUR POST TITLES AS QUESTIONS. THANKS. CHRIS]
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no lens or prism is required ... http://en.wikipedia.org/wiki/Pinhole_camera , the projected image is upside down though.
[The only source of light in the room should be from the pinhole,
i.e. the room should be blacked out. The outdoor scene should be well lit, ideally in bright sunshine].
also see ... http://en.wikipedia.org/wiki/Camera_obscura
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Thanks for the reply. What about attempting to carry the image nine feet to the basement? Is it possible to flip the image again so it isn't upside down? To me it seems some kind of periscope will work better. Projection sounds great but there seems to be a problem with how much light is projected from outside to make it all the way down to the basement level. [O8)]
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A periscope is the basic idea, but the periscope allows you to view the image of what's upstairs because your eye has a lens that forms an image on your retina. You'll need to put a lens in to focus the light coming out of the periscope onto your wall so that you can project an image onto it.
The pinhole basically takes the place of a lens to let you do imaging. If you wanted, you could put a pinhole after the periscope.
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Thanks JP. I was kind of thinking along the same lines. I was hoping to find someone that has tried this before. I plan to build something before construction of the basement to see if I can get good results. Not sure where I will find a big enough lens. I once had an old photo developer. I knew those lens would come in handy one day. Too bad I didn't save them. [O8)]
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The original camera obscuras (what is the plural there?) didn't use a lens- they used the pinhole effect.
It would be quite difficult to get a lens with a long enough focal length to do the job well. Some rather weak reading glasses might be OK
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If I remember my Latin correctly plural of camera (trs. chamber; female first declension noun) would become camerae in the nominative plural and obscura would be obscurae - ie camerae obscurae. But the accepted plural in english is camera obscuras; as you had it.
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That was just the information I needed. It took me to this:
Mirrors and Lenses
Obscuras with mirrors and lenses, which emerged during the late 16th century, were more sophisticated than the previous pinhole obscuras. Some used a mirror positioned at a 45-degree angle in reference to the path of light. This helped to correct inverted images so they could be seen right-side up and left to right. Also, placing a small piece of glass over the cut out hole, to create a lens, produced images that were more clear and vivid. [O8)]
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