[Leica] Persepective and natural viewing distances

["Mark E Davison" <dmark8@qwest.net>]

For a given print, there is a unique viewing distance that will recover the
angle relationships of the original scene (known as the viewpoint in
traditional perspective drawing and painting.) If you view a print from the
correct viewpoint, there will be NO percieved angular distortion in
wide-angle shots, and no perceived compression in telephoto shots.

For a horizontal print on 35mm film printed full frame without cropping, the
distance from the viewpoint to the print is:

(lens focal length / film image height) * height of print. =

(lens focal length / 24mm) * height of print.

So, for example, for an 8 x 10 printed without borders and a 50mm "normal
lens", the natural viewing distance is

(50mm / 24mm) * 8inches = roughly 16 inches, which is very close to the
usual reading distance people adopt.

For a 24mm lens, the natural viewing distance is

(24mm / 24mm) * 8 inches = roughly 8 inches, which is closer than most
people look at a print. Viewed from 16inches away, you get the familiar
wide-angle perspective "distortion" , such as egg-shaped heads.

For a 100mm lens, the natural viewing distance is

(100mm/ 24mm) * 8 inches = roughly 32 inches, which is further away than
most people look at the print. Viewed from 16inches, you will see image
compression.

This explains the oft-heard comment that 50mm lenses reproduce the "natural"
perspective of the scene.

It also explains why shots with wide angle lenses often look so natural
blown up to double page spreads in big books--your default viewing distance
comes closer to the correct viewing distance for the image. 16" x 24" is a
good size for 24mm shots, yielding a 16" natural viewing distance.

I believe that when people talk about "perspective" effects in lenses, they
are really talking about psychological effects which arise from looking at
images at other than their natural viewing distances. These effects are real
and can add drama to your images.

Mark Davison

 ----- Original Message -----
From: "Johnny Deadman" <john@pinkheadedbug.com>
To: "LUG" <leica-users@mejac.palo-alto.ca.us>
Sent: Wednesday, June 06, 2001 6:01 PM
Subject: Re: [Leica] 28 mm M Lens recommendation


> on 6/6/01 8:07 PM, Gil, Miguel (US - Los Angeles) at mgil@deloitte.com
> wrote:
>
> > Frank,
> >
> > Given two lens at the same distance from the subject, a 21 mm will give
a
> > different perspective than a 600mm.  The 600mm compresses distance
between
> > the foreground and the background.
>
> no they just give different FRAMES. The perspective is the same.
>
> 'Perspective' has quite a specific and precise meaning unless you want to
be
> humpty dumpty and have it mean whatever you want it to mean, which is
fine,
> but our conversation's then over.
> --
> John Brownlow
>
> http://www.pinkheadedbug.com
>
>