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pinhole microscope

For larger depth of field
  [vote for,

As far as I remember, pinhole cameras have a strange feature - all objects are focussed regardless of the distance.
So I reason that if a CCD device was used with a real pinhole, then it could function as a microscope just by placing the pinhole very close to the object.
For reduction of distortion, the CCD ought to be hemi-spherical in shape.

The advantage would be that everything would be in focus. The front and rear legs of that nasty looking spider would all be visible. Conventional (except confocal) microscopes have a very small depth of field.

Before everyone shouts: "Pin hole cameras are baked", I believe they have a very small lens, which means they have a focal length and wouldn't do the job.
Ling, Jan 28 2005

Vermeer's Camera http://www.grand-il...ermeer/vermeer1.htm
Interesting study of 17th century painting made using a camera obscura (first as a pinhole camera then with a lens) [FarmerJohn, Jan 28 2005]

Pinhole microscope that everyone can try http://www.topscien...mples/topscope.html
See the boxed description a little way down the page. [Ling, Jan 30 2005]




       How to put this.....   

       Might work?   

DesertFox, Jan 28 2005

       Try a Google search on "digital pinhole"
normzone, Jan 28 2005

       A pinhole camera whose pinhole size is 'p', whose distance to the film is 'f', and whose distance to the object is 'o', will have a "blur" on the film of size p+p/o); this size blur will correspond with a size of p+p/f at the object. Consequently, to get any useful resolution, the pinhole must be extremely small. Unfortunately, a small pinhole isn't going to get much light through. CCD's may be pretty sensitive, but they have definite limits; I don't think you could image anything usefully through a pinhole microscope without using a super-cooled CCD. Even long exposure times wouldn't make up for the amount of noise a room-temperature CCD would pick up.
supercat, Jan 29 2005

       Could you compensate for that by shining more light on the subject?
robinism, Jan 29 2005

       //Could you compensate for that by shining more light on the subject?//   

       If you were viewing things like crystal formations and such, you might be able to. But if you were trying to view things like bacteria, the amount of light required would destroy the specimens.
supercat, Jan 29 2005

       Thanks, [normzone], I managed to find a reference that uses no CCD. Anyone can try it.
[Supercat], additionally, a very small pin-hole will have more diffraction. I suppose it depends on how much magnification is required, and how much depth of field, at a low cost.
Ling, Jan 30 2005

       On any microscope, depth of field could be increased pretty easily by shrinking the objective lens. Generally, however, having a nice bright picture is more important than having a large depth of field.   

       BTW, soft-focus lenses can also increase depth of field, at the expense of clarity in the focal plane.
supercat, Jan 31 2005


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