Biggest Pinhole Camera Ever

universetoday.com ^ | Oct 1, 2004

[ckilmer]

Biggest Pinhole Camera Ever

Summary - (Oct 1, 2004) A common science experiment for young kids is to build a pinhole camera. Researchers from the University of Colorado at Boulder think NASA should build a gigantic one in space and use it to find planets orbiting other stars. The "New Worlds Imager" would be a football field-sized opaque light shade with a small opening right at the centre to let light through. A detector spacecraft would sit thousands of kilometres back and collect the light that comes through the opening. The shade would block the light from the star and let astronomers detect planets orbiting it. The proposal was one of 12 advanced concepts recently selected for further study by NASA.



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[Covenantor]

Suddnely my grade school oalmeal container pin-hole camera seems....so small.

[Shellback Chuck]

Won't work, too much "stray" light between "pinhole" and "detector" spacecraft.

[hyperpoly8]

Alignment would be difficult, but it's a wonderful idea.

[ckilmer]

if there is too much stray light between the an acre of "paper" in space and a sattelite with a basketball target--then why is there not too much stray light between a pin hole and white paper on earth.

[Kirkwood]

It would be EXTREMELY inefficient, but relatively cheap.

[dr_lew]

Gosh. I had this idea years ago. The thing is you have to match the diffraction limit, which decreases with hole size, with the geometric limit, which increases with hole size. It turns out that for a given pinhole-observer distance, L, the optimum size is approximately the geometric mean of L and lambda, the wavelength of light. lambda ~= 5e-7 meters . So a one-meter pinhole is appropriate for L = 2e6 meters : 2000 kilometers.

I decided it was a stupid idea. Because if your going to use a one-meter aperture, why not just make a telescope?

[Kirkwood]

The sensor array might be apodized for the position of the "pinhole" to reduce stray light effects.

[Shellback Chuck]

Light is collective, hence the amazing example of "time exposures", how far was your pinhole from your paper, here on earth?? not too far I bet. I also bet you were looking at something relatively bright, like the sun during an eclipse. Now take that example into space with a pinhole diaphragm thousands of meters from a detector (the film) and try to shield the detector from all other light sources other than the diaphragm. Too much stray light to interfere with the sensor. Stars, planets, nova's, galaxies, little green men, etc.

At those kind of distances you would still need some kind of lens to focus in on the pinhole, so you would still result in some chromatic aberration

[Kirkwood]

No need for any lens. The photons just pass directly from the pinhole to the sensor array. You could put low-ech light baffles around the individual sensors to cut out on some stray light, but it would still be a problem. The pinhole material itself would have to be anti-reflective.

[Kirkwood]

low-ech = low-tech

[Shellback Chuck]

I think dr_lew has this problem down pat.

[dr_who_2]

Sounds like an enormous focal plane array.

[notforhire]

Your probably right, but I thought light had to be reflected in order to be "visible" and since space is a vacuum....

[Shellback Chuck]

In space there would be billions of direct sources of light all around.

[Shellback Chuck]

"It was full of stars"......2001

[NicknamedBob]

This can be simulated by simply letting the moon, with its crags and fissures, occult the star for you. You would have to be quick, but the technique of shielding one's eyes with his hand should yield some results.

[Kirkwood]

It would be similar to a giant ccd array with a giant pinhole positioned in front of it. At least that's how I envision it.
I still prefer a bunch of nuke-power hubble-like telescopes with ion positioning thrusters working together.

[Fiddlstix]

Bump
For Later

[notforhire]

Absolutely! But, I just picture (no pun intended) the images of Armstrong on the moon. There was no atmosphere to reflect the light and it appeared as though he was in complete darkness even though he was standing in direct sunlight.

I don't know. As I said, you’re probably right.