RE: Why does light pass through a lens?

[Chris <cjrs@xxxxxxxxxxxxxxxxx>]

“Some have reversed the question:  what if you put a lens in from (back) of a pinhole?  I'll let you figure that one out, if you can...  -:)”

Then it is a normal camera with a stopped down lens.

 

Chris

 

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From: owner-photoforum@xxxxxxxxxxxxxxxxxx [mailto:owner-photoforum@xxxxxxxxxxxxxxxxxx] On Behalf Of Guy Glorieux
Sent: 01 January 2009 17:10
To: List for Photo/Imaging Educators - Professionals - Students
Subject: Re: Why does light pass through a lens?

 

 

 

 

Ahah! So what kind of an image would you get if you drilled a pinhole in
the center of a glass lens?

Greg

Oooops!   A pinholed lens?

I've tried to find funny answer but I just couldn't.  So here are some thoughts.

1.  You'd get an image with a tiny white imageless hole in the center.  This is because the thickness of the glass lens would prevent a pinhole image to actually form. The reason we use extremely thin brass shim in which to drill the pinhole is to ensure that the vignetting arising from the thickness of the shim is reduced to a minimum.

2.   If you could design an extremely thin glass lens and drilled a pinhole in the center, then you would have two images that should normally perfectly overlap since the lens focal length would be identical to the focal length of the pinhole.  However, since each lens will have their own distortion features, the pinhole and the lens will not produce identically configured images. 

3.   Evidently, the pinhole image would be washed out completely by the lens image since the effective aperture of the pinhole would be far less than that of the lens.

Some have reversed the question:  what if you put a lens in from (back) of a pinhole?  I'll let you figure that one out, if you can...  -:)

Happy New Year!

Guy