Archived posting to the Leica Users Group, 2003/03/04

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Subject: Re: [Leica] wideangle observations WAS 21mm Skopar opinion(s) please
From: Jerry Lehrer <jerryleh@pacbell.net>
Date: Tue, 04 Mar 2003 18:47:56 -0800
References: <D704B31B-4EAE-11D7-8697-000393462E70@johnbrownlow.com>

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
> >
>
> --
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In reply to: Message from Johnny Deadman <lists@johnbrownlow.com> ([Leica] wideangle observations WAS 21mm Skopar opinion(s) please)