Re: fisheye or roundshot?

[Jook Leung <jook360@xxxxxxxxxxxxx>]

To provide this discussion list with a visual example, I posted an image
taken with a Roundshot 220vr camera and a Sigma 15mm full frame fisheye
lens.

You'll notice that the base of the camera (the battery) is in focus while
everything further out is smeared.

I had no published info on where to set the rear nodal point "h value" for
this lens, so I used "a take a guess value" for the 14mm Sigma 2.8EX lens
but that's the rectilinear version.

http://360vr.com/pages/rs_fff_test.html


regards,
Jook


>On 15 Apr 00 at 13:49, Glenn Barry wrote:
>
>> The easy way to see this is to put the lens on look through the viewfinder
>> or ground glass and watch the degree of image distortion as you rotate the
>> camera. Fisheye mapping and compression requires that this is quite severe,
>> more so at the edges agreed, but it is present throughout the frame
>> including the centre. Just look at a straight line in the middle of the
>> frame. It must begin to curve the moment you rotate the lens due to the
>> fisheye projection. There will always be some blurring.
>
>It is claimed that only a single-pixel wide digital 'slit' can overcome
>this blurring problem....in that case, no pixel is exposed at more
>than one rotational position, unlike any photo-chemical registration
>with a meaningful slit-width (a slit would have to be smaller than a
>hair to mimick the digital one-pixel concept, which would kill the
>image due to diffraction (remember that the digital slit is not a
>slit, but only a recording single row of pixels, so diffraction is
>not relevant there).
>
>Not quite sure whether it is valid to explain the blur itself with
>the varying magnification of a fisheye....a rectangular lens has the
>same magnification from corner to center, a fisheye does not I
>believe (this even goes as far as the claim that a 14mm fisheye has
>less variety from corner to center than a 17mm fisheye with the same
>overall angle of view, hence the fisheye 'effekt' of the 17mm is
>larger).
>And since film speed of a rotating camera is depending on
>focal length, this is exactly the problem....no speed can suit both
>center and edge at the same time.
>
>--
>Bye,
>
>Willem-Jan Markerink
>
>
>      The desire to understand
>is sometimes far less intelligent than
>     the inability to understand
>
>
><w.j.markerink@xxxxx>
>[note: 'a-one' & 'en-el'!]


=============================================================
JOOK LEUNG
360VR Photography
44A Honeck Street
Englewood, NJ  07631
http://360vr.com   voice: 201.894.5881    fax: 201.894.5882
http://bigapplepenthouse.com