Re: IR spherical panorama

["Willem-Jan Markerink" <w.j.markerink@xxxxx>]

On 16 Oct 00 at 0:20, Otto Giesenfeld wrote:

> --Ben Kreunen <ben@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
> 
> > One problem that I have found though is that I was getting some 
> > considerable light fall off towards the edge of the images.  I'm shooting 
> > with an 8mm circular fisheye, one of the benefits of which for this sort
> > of  work is that there is no light fall off with normal films. With IR
> > film  however, it appears to be quite pronounced.   The sharpness across
> --
> > Film was Konica IR, stupidly shot handheld as I was testing a new method
> > of  aligning the camera. (1/8sec @ f4, hence some of the blur) I've added
> --
> > Sigma, manual focus f4..  only a #25 (internal filter).
> 
> Have you done any of your non-IR spherical panoramas at full aperture? (One
> might think that it would seldom be needed, given better film speed and
> less filtration.) If not, the lens may simply have some light fall-off at
> f/4. Which may have gone unnoticed in any pictures, IR or non-IR, you have
> taken for purposes other than spherical panoramas.

Oh, and to quote David Ruether (aka Bob Neumann on Usenet): the Sigma 
8mm/f4.0 is one of the very few lenses which decreases image circle 
when stopping down....most other lenses increase image circle when 
stopping down (don't ask why, I guess it's quite complicated....;)) 
Most likely a tribute to the very complex design (with the added 
restriction/demand of having a screw filter inside (for which the 
lens must separate in two....I believe only the Sigma 21-35mm shows 
the same exotic design).
Perhaps you used indeed a different aperture than normally?
Konica IR + #25 is 8 ASA when I recall correctly....that's way 
outside the range of normal film....

--                 
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'!]
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