Archived posting to the Leica Users Group, 2003/03/04
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]John Finally, a voice of reason here. Someone who understands the physics of photographic optics, and can express it so you all can understand it. Jerry Johnny Deadman wrote: > A couple of points here: > > 1) All rectilinear-drawing wide-angle lenses have distortion. Objects > at the edges are stretched out in order to preserve straight lines. You > can preserve dimensions at the expense of the lines in a fisheye lens, > which is no more or less distorted, just distorted differently. For > many applications a fisheye may be preferable because it requires few > design compromises and covers a greater area for a given focal length > (eg a 15mm fisheye on 35mm gives 180 degrees FOV across the diagonal -- > very useful for stitched QTVR panoramas). > > The only way to get an undistorted wide angle image is to map the image > to the inside of a sphere and view it from the center like a > planetarium. It is in fact quite possible to do this using regular > lenses and cameras using software like ptGui (www.ptgui.com) and ptMac > (www.kekus.com), both of which are shareware, work amazingly well, and > are based on Helmut Dersch's open source Panotools suite. > > Therefore if you mean that the lens doesn't have much barrel > distortion, it's worth saying so. > > A cylindrical projection is halfway between a rectilinear (standard) > and spherical (fisheye) lens. This is rectilinear in one dimension and > curved in the other. Here is a link to a bunch of cylindrical 360 > degree panoramas that give you the general idea. Note that the last > one, which is a forest landscape, does not appear to be distorted at > all because the only straight lines are in the vertical direction. > > http://www.pinkheadedbug.com/wip/360/index.html > > In fact ALL rectilinear lenses feature dimensional distortion but you > only really notice it in wide-angles. > > There is no such thing as an undistorted lens, any more than there is > an easy way of mapping the surface of a sphere into a plane. In fact, > if you think about it for a moment, you will see that in many respects > these are the same problem. > > 2) Mark is dead right about the Skopar. > > On Tuesday, March 4, 2003, at 08:30 PM, Mark Rabiner wrote: > > > Seth Rosner wrote: > >> > >> 21/3,4 Super-Angulon. Dick Gilcreast reviewed a bunch of 21mm lenses > >> in LHSA > >> VIREFINDER two or three years ago. 21mm is not how I see > >> but I did use the Super-Angulon a bit some years ago and found this > >> lens to > >> be very good indeed, alm ost no distortion. > >> > >> Seth > >> > > Sieff's work was all about the 21/3,4 Super-Angulon. A very > > distinctive lens which is apples and oranges from the Scopar. I don't > > think the 21/3,4 Super-Angulon cost an arm and a leg at this point. > > Have what a current 21 cost. A very compact lens someday i hope to get > > one. I'd wait a few more paychecks and get one An amazing classic. > > A Schneider lens on your Leica what could be more cool! > > > > My approach is you're shooting with the greatest camera there is no way > > chince on the glass? > > > > It's the glass that takes the picture, not the exposure meter. > > > > > > Mark Rabiner > > Portland, Oregon USA > > http://www.rabinergroup.com > > Email: mark@rabinergroup.com > > Fax: 503-221-0308 > > -- > > To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html > > > > -- > To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html