On 11 Nov 2005 at 16:08, Boris Liberman wrote: > Rob, I see your point... But I have just one concern here... I tried to > stitch few images shot with 43 Ltd. Prior to that I only used 77 Ltd or > wide end of F 70-210... Apparently when I moved the 43 Ltd every so > slightly I changed the relative position of some elements in the frame > in such a way that stitching became geometrically impossible.
Hi Boris, As Bill said your image sequence likely suffered from parallax error where the lens wasn't being rotated about its nodal point, see the following link for a good description of the problem: http://www.path.unimelb.edu.au/~bernardk/tutorials/360/photo/nodal.html >From a practical point of view if you wish to set up a rig with parallax compensation all you need is something like a macro-rail which will allow the camera/lens to be moved behind the tripod heads natural point of rotation. On my kit I use a Manfrotto macro rail which has a graduated scale down the side. I've empirically determined the correction factors for all my lenses so all I do is look up my little printed table and dial in the appropriate offset. (Dave Savage can attest to how practical it is). How I determined the offsets for my various lenses was to set up a pair of high intensity narrow beam LEDs, one close to the camera and one in the distance. I then aligned them so that when the camera was perpendicular to them I could see only a single lamp. As the head was rotated I adjusted the offset until the lamps remained precisely in line. Beware though that the offset will change slightly with FL, all mine were measured at infinity. You can see a pic of my nodal point testing set-up here: http://home.swiftdsl.com.au/~distudio/temp/IMGP2882.jpg (~86kB) The geometric distortions inherent in the lens and the spatial remapping are taken care of by the pano software but all image sequences will suffer from parallax error if not set up properly. However it's effect is more obvious when objects are in close proximity to the camera so often long lens sequences of distant objects require no parallax compensation to produce a great pano. > What came to my mind this time is that, perhaps, by applying PTLens one > can "flatten" (or de-fish, if you will) the view hoping to compensate > for the effects I described above. It's just not possible, it's like trying to create a true polarizing effect after the shot has been taken. > Anyway, Mark Roberts seems to be using 31 Ltd most of the time for his > panos. What probably matters more is being free of any geometric > distortions in the frame... Not really, I often shoot panos with a fisheye, the geometric distortions are pretty severe but the pano software contains a mathematical description of the distortion so that it can effectively negate the geometric distortions. > I suppose I should be arranging for some experiments. With AutoStitch it > is extremely easy, almost too easy, I might add. Easy comes with trade-offs, it's a great little package but for anything that I wish to produce with accuracy and control I still use manual tools. Cheers, Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://members.ozemail.com.au/~distudio/publications/ Pentax user since 1986, PDMLer since 1998
