[MF3D.FORUM:53] Re: Apparent image size, MF verus

[Alan Lewis <3-d@xxxxxxxx>]

I've modified Paul's very good table again, using the ideal situation
where the full frame size is used for apparent size comparison vs.
diagonal measurement.  I keep doing this because the mask size is a
mechanical limitation applied by the limitations of equipment.  To first
understand the relationships between formats I like to isolate the
variables to see where the problem first occurs.
(BTW: Paul's use of this table idea is working very well.  We all see it
in our own way, none of them necessarily the final word, just a tool).

 Format     Size       Diag      Viewer Mag       Apparent size
 ------     ----       ----      ----------       -------------
 5P         23 x 24    33.24     7.52 (250/diag)    250.00
 7P         24 x 30    38.42     6.51 (250/diag)    250.00
 MF         60 x 60    84.85     2.95 (250/diag)    250.00
 3Disc      24 x 36    43.27     5.78 (250/diag)    250.00
 6x7        60 x 70    92.20     2.71 (250/diag)    250.00

Paul wrote:
> Most of these numbers are trying real hard to come out to
> be 250mm, aren't they??!!

Yes, and they don't have to try very hard.  I'm finally beginning to see
the logic with all this analysis.  Even though it appears very basic in
concept I sometimes need to see the simple stuff presented in this way
to finally understand it. This table uses redundant calculations, but in
this case they help to illustrate what is happening.

> 
> So I now propose the Lewis-Talbot-Glickman rule of stereo WOW
> effect:
> 
>     The "apparent image size" of an image (measured diagonally)
>     is constant (250mm) across film formats if the FL of the
>     viewer lenses is "normal" (equal to the diagonal) for the
>     masked size of the image.

The table illustrates this observation.  Thanks Paul.

> 
> Practical consequences of the rule:
> 
>     - Apparent image size is reduced when the viewing lens
>       FL exceeds the diagonal of the masked image--whether
>       due to high levels of cropping (e.g., the 50x50 MF
>       mounts), or to the viewer lenses being significantly
>       longer than the shooting lenses (e.g., Realist).
> 
>     - Apparent image size can be increased by either shooting
>       with wider than normal lenses (and viewing orthostereo-
>       scopically); or by viewing with higher power, but
>       "squashy," lenses.  Example: shooting 6x7 with 78-80mm
>       lenses instead of 92mm lenses.
> 
> The table also sugggests one reason why MF seems to have so
> much WOW for most people's first impression:  they are used
> to the Realist 5P format, which falls *far* short of the 250mm
> "normal" apparent diagonal.

Yes, that is what I am finally understanding.  It appears that all
stereo format sizes start on equal footing as to ideal "apparent image
size" but mechanical limitations (or design choices) modify each
format's final size and effect.

> 
> I do still acknowledge that there are other components to the
> WOW effect that favor MF.

Yes again.  I will still say that you need the vertical size as well as
the horiz. size to get the best immersive feel.  The world is just as
vertical as it is horizontal.

The diagonal apparant image size helps us to understand the relationship
of all the format sizes.  But the vertical/horizontal apparent image
size (the tables up to now) take into account how the image will
"feel".  The diagonal size doesn't indicate the "feel" of the final
image.

The most immersive feel will happen when the entire lens diameter is
filled with an image.  Rectangular images do not fill the entire
diameter. (You can use rectangular lenses in the viewer to fill the
entire area of the lens, but this doesn't change anything.)

So one way to get an immersive feel is to use viewer lens f.l. equal to
the horizontal size of the negative (not the diagonal as is usually used
for calculation).  For instance on a 6x6 format the viewer lens will be
60mm (not 80mm as is normally used).  I have tried this and it works.
You get a full circle of image in the lens.

I'm splitting hairs here with some of this.  You can get an immersive
feel with any format by using shorter f.l. lenses.  I am just trying to
define the ideal situation in order to understand it. We can then
understand where the practical compromises are.

-- 
Alan Lewis  
mailto:3-d@xxxxxxxx
http://members.home.net/3-d
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