Re: [Phys-l] pinhole camera

[Michael Porter <listmoe@gmail.com>]

On Apr 12, 2007, at 5:21 PM, Edmiston, Mike wrote:
> My definition of real image would be more like... Light passing  
> through
> a particular point on the image came from a particular point on the
> object.  That is, I see the object-image relationship as a one-to-one
> mapping of light from one point on the object to one point on the  
> image.
> A pinhole does that.  A pinhole does not do that perfectly, but as  
> John
> Denker said, a lens doesn't do that perfectly either.

I have to say, I'm a little surprised at what I see is a somewhat  
fuzzy definition of an image that people are coming up with (no pun  
intended...). Should we tighten it up a bit? Aren't we all about  
nailing down the nit-picky details? ;-)

Yes, there is a recognizable "picture" on the screen of a pinhole  
camera. But are we justified in calling it an image and linking that  
picture to those created by lenses, imperfect as they may be?

With a lens, the image is located where the least-objectionable (most  
tightly focused bundle of light rays) image is located.
What about a pinhole camera? No matter where you put the screen,  
there will be a reasonably acceptable "image", possibly as good as a  
lens. But the rays are diverging right from the object. So where is  
the image? Everywhere? Or nowhere?

---
Michael Porter
Colonel By Secondary School
Ottawa, Ontario, Canada