Re: Image diameter ....?

"Donn Cave" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> Quoth "Richard Knoppow" <[EMAIL PROTECTED]>:
> ...
> |   Tilting the field can cause some geometrical
distortion
> | but it is different from that produced by shifting since
we
> | are usually still in the center of the field where
shifting
> | off-sets the center toward one side of the image.
> |   This is much easier to explain where one can draw
pictures
> | or demonstrate the effects.
>
> Verbal explanation is sure a problem, but maybe not as
hard
> as you're making it!  I would put it like this (hm, was
anyone
> asking, or are we just explaining something we all know to
each
> other?  Oh well!)  In my explanation, there are two simple
> things to consider:
>
> 1.  Angle of film in relation to the subject.  Normally
>     parallel to subject vertical, and the viewer naturally
>     expects this orientation.  Hence, "correct"
perspective
>     is achieved by maintaining this parallel relationship
>     despite an angle of view that may not be quite
horizontal.
>
> 2.  Angle of lens to film.  Normally parallel, except to
>     achieve some manipulation of the normal depth of
field.
>
> So back tilts are confusing and difficult because they
affect
> both, but I suspect a lot of great photos have been taken
with
> some judicious back tilt.  In terms of perspective, it
really
> is the same as rise, and it sure makes more of a lens'
coverage
> limits.
>
> Donn
   When back AND front tilt are used together to get the
back and lens parallel it is the equivalent of rise. The
tilt available in some cameras can be combined with rise to
get even more rise if you need it for some reason.


-- 
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Richard Knoppow
Los Angeles, CA, USA
[EMAIL PROTECTED]