wwp@yahoogroups.com:
Re: Sigma 8mm / Hyperfocal
Erik Krause 2004-Dec-02 23:21:00
On 24 Nov 2004 at 6:32, Landis wrote:
> I have tried the hyperfocal method previously and
> gotten blurry images. I've tried halving that
> (ie shooting at f/16 and setting infinity at f/8)
> and I still get blurriness in the distance. I
> don't have any problems with this approach with
> the Nikkor 10.5 FE, so I chalked this up to just
> being the way of the Sigma 8.
Hyperfocal distance is based on depth of field calcualtion and DOF is
based on the blurriness you can or can not percept in the final
image. All standard DOF tables and most caculators are based on paper
prints viewed from standard distance (app. print diagonal) and the
resolution of standard human eyes.
As you can imagine a stitched VR panorama is far from a print
regarding those parameters. Given two same sized panoramas you need
far less magnification for a 10.5 mm full frame than for a 8mm
circular fisheye.
Not only because of the longer focal length but the fact, that focal
length changes with distance from the image center, too. Because of
this the edges of a circular fisheye image have to be magnified much
more than the edges from a full frame fishey image.
The key parameter to DOF calculation is the maximum allowed diameter
of the circle of confusion. For a digital camera this diameter must
be set to two times the pixel diameter (one pixel alone can't show
blurriness) to do DOF calculations for maximum possible sharpness.
Another approach could be the "optimum aperture" as described by Ken
Rockwell: http://www.kenrockwell.com/tech/focus.htm
This approach takes the diffraction into account, that blurs the
image the more you stop down.
However, all this thoughts and calculations are based on non-fisheye
lenses. For fisheyes anything might be a bit different...
best regards
--
Erik Krause
Ressources, not only for panorama creation:
http://www.erik-krause.de/
Read panotools at GMane:
http://news.gmane.org/gmane.comp.graphics.panotools