Re: fisheye or roundshot?

[gene360@xxxxxxxxx]

Is it possible to set the nodal point oppposite of what was set to (hopefully)
forced the reverse to happen? (instead of the battery in focus & top smeared > to
having the top look normal & the battery smeared)

Just a thought!

Jook Leung wrote:

> 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