Archived posting to the Leica Users Group, 2004/11/03

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Subject: Levelling: [was Re: [Leica] More snaps (Skopar)]
From: r.s.taylor at comcast.net (Richard S. Taylor)
Date: Wed Nov 3 10:33:14 2004
References: <r02010400-1035-60B9BD392DAE11D98C24000A957A8242@[67.86.119.182]>

That's an interesting number.  If I did the math right, it works out 
to about  0.025 degrees.  So why is it so hard to level the camera 
with a wide-angle lens?  I suspect the answer is in the 
"minification" and restricted field of view of the usual finders. 
Visual size reduction plus shorter baseline equals greater error. 
The finder brightlines, if it even has them, might easily be off by a 
degree, too.  Without brightlines, leveling is probably hopeless 
since your eye has no reference as to what is square.

Accurate reference lines in the finder are the only answer, as was 
mentioned earlier this morning, but the the lines must be confirmed 
square to the camera film gate, too.

Photoshop is easier.  How did we ever live without it?




>I had an interesting discussion with a cabinet maker and later with an
>Intensive Care physician several years ago about the ability of our
>"uncalibrated eyeballs" to discern "out-of-true" lines.  Cabinet makers,
>I learned, have always known that the unaided human eye (assuming
>average eyesight), can detect 1/64" and 1/128" over a length of 3'.  The
>physician was treating my wife, who had a Swan-Ganz (sp?) catheter.  For
>the treatment to work properly, as I recall, a long level had to
>extended horizontally from the catheter entry site in her chest out to
>the side of the patient.  Several nurses were fussing with the thing
>when the doc came in and, rather impatiently explained to the nurses
>that the human eye was more capable of detecting out-of-level conditions
>than by using the level.  He then proceeded to demonstrate, and he was
>right! 
>
>Amazing what the eye can do! 
>
>Ken Frazier
>
>_______________________________________________
>Leica Users Group.
>See http://leica-users.org/mailman/listinfo/lug for more information


-- 
Regards,

Dick
Boston MA

Replies: Reply from s.jessurun95 at chello.nl (animal) (Levelling: [was Re: [Leica] More snaps (Skopar)])
Reply from dorysrus at mindspring.com (Don Dory) (Levelling: [was Re: [Leica] More snaps (Skopar)])
In reply to: Message from kennybod at mac.com (Kenneth Frazier) ([Leica] More snaps (Skopar))