[translated from German to English]

FROM: Helmut FAUGEL 
SUBJECT: Re: Fisheye vs Extreme Wide-Angle
DATE: Tue, 26 Jan 1999 09:35:41 +0100
ORGANIZATION: IPP Technologie / ICRH
NEWSGROUPS: de.rec.fotografie

Alexander Kraus wrote:
> Eduard Spanninger wrote: 
> > Laurent Wirmer wrote (23.01.99):
> >
> >  LW> A fisheye has a completely non-corrected, very strong barrel-like
> >  LW> distortion. With a normal (rectalinear) 14mm this distortion is 
> >  LW> corrected almost completely.
> >
> > But how come *both* use optical elements, with surfaces that are part of 
> > a perfect sphere? Normal 14mm's are not necessarily fitted with 
> > aspheric elements, right? Or has the first nothing to do with the latter?
> 
> The first has indeed nothing to do with the latter. It's even the other way 
> around, fisheyes have a very 'flat' sphere as front element. How in spite 
> of this it still can get 180 degrees on film is a mystery...

Oh, the explanation is quite simple:

Why do we call a fisheye a fisheye? Rudolf Kingslake, in his book
'A History of the Photographic Lens', writes on page 145 the following:

"The name fish-eye was coined by R.W. Wood(*) to refer to any lens
capable of imaging the entire hemisphere in object space onto a 
finite circle in the focal plane(3). He chose this name because a fish
looking upward at the surface of the water will see the whole sky 
imaged as a finite circle this way"

(3) R. W. Wood, 'Physical Optics', page 67. Macmillan, New York, 1911

(*) Among other things discoverer of the socalled 'Wood' effect. In 
    1910, he was the first to use IR-sensitive plates for ordinary 
    photography, and discovered the high reflectance of foliage.


Na und was die Fische koennen, koennen die Optikrechner spaetestens
seit Hills 'Sky-Lens' von 1924 auch. Im Prinzip handelt es sich
bei den Fisheyes um nomale Objektive denen zur Brennweitenverkuerz-
ung eine starke Zerstreuungslinse vorgesetzt wird die objektseitig
ziemlich eben ist. Dadurch verursacht sie eine aehnlich starke
tonnenfoermige Verzeichnung wie der Blick an die Wasseroberflaeche.

And what the fish can do, have optical engineers also managed since 
Hills "Sky-Lens" in 1924. Basically a fisheye is nothing more than a 
ordinary lens with a very strong diverting lens up front, which is 
very flat on the front side. That is why it creates a similar 
barrel-distorted image like a fish sees though the water, looking up 
in the sky.

-- 
Helmut Faugel





FROM: glasairdeja@my-deja.com
SUBJECT: Demonstrating a fisheye view
DATE: Thu, 25 Jan 2001 22:42:11 GMT
ORGANIZATION: Deja.com
NEWSGROUPS: sci.optics

A fish sees a compressed view of the world since a large field angle
in the air above the water is mapped into a narrower cone angle in
the medium of the water.  That is way they call a photographic lens
with large built-in barrel distortion a fisheye lens.  It should really
be called a "fish view lens" since I don't think the eye of the fish is
responsible for what it sees as much as the fact that its eye is
immersed in water.
All around this circular field of view would be dark or black as that
is the view of the bottom of the lake totally internally reflected by
the surface of the water.
How could I demonstrate this?  The camera would have to be immersed in
the water, or at least the front of the lens and would have to be
waterproof.  If the camera is in a watertight enclosure, including,
then the water just acts as a window and the cone angle into the camera
lens is the same as the angle above the water surface.  Maybe an
endoscope or something?


Sent via Deja.com
http://www.deja.com/







FROM: Ian Stirling 
SUBJECT: Re: Demonstrating a fisheye view
DATE: Fri, 26 Jan 2001 02:06:35 GMT
NEWSGROUPS: sci.optics

glasairdeja@my-deja.com wrote:
>A fish sees a compressed view of the world since a large field angle
>in the air above the water is mapped into a narrower cone angle in
>the medium of the water.  That is way they call a photographic lens
>with large built-in barrel distortion a fisheye lens.  It should really
>be called a "fish view lens" since I don't think the eye of the fish is
>responsible for what it sees as much as the fact that its eye is
>immersed in water.

You can get at least some idea by looking in the side of a rectangular
fishtank.

-- 
http://inquisitor.i.am/    |  mailto:inquisitor@i.am |             Ian Stirling.
---------------------------+-------------------------+--------------------------
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He wouldn't have made them out of MEAT!                           - John Cleese

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