Archived posting to the Leica Users Group, 2003/03/04
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]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