Re: [tech-3d] Digest Number 33

["Don Lopp" <dlopp@xxxxxxxxxxxxxxx>]

Having built 10 MF viewers with lenses with focal legths of from 45mm to
80mm., I have come to the conclusion that shorter is better. An example is
that I prefer to view  80mm stereo slides with viewer lenses of about 50mm
because this makes the views look like Eyemax which is more than I can say
about viewing 35 mm stereo when using the standard available viewers which ,
mostly, have lenses of 42 to 45 mm lenses. My viewer with 28mm lenses is
pretty good, but I wish I could find some 24 mm lenses that are useable ?
DON
----- Original Message -----
From: <tech-3d@xxxxxxxxxxx>
To: <tech-3d@xxxxxxxxxxx>
Sent: Thursday, November 23, 2000 12:50 PM
Subject: [tech-3d] Digest Number 33


>
> There are 4 messages in this issue.
>
> Topics in this digest:
>
>       1. Re: holographic 3d
>            From: lunazzi <lunazzi@xxxxxxxxxxxxxx>
>       2. Re: Stereo Base Calculation with a $20.00 Handheld
>            From: "Michael K. Davis" <zilch0@xxxxxxxxxxxx>
>       3. Why consider ratio of Viwer FL to Camera FL?
>            From: "Michael K. Davis" <zilch0@xxxxxxxxxxxx>
>       4. Re: Re: Stereo Base Calculation with a $20.00 Handheld
>            From: Andres Posada O <aposadao@xxxxxxxxxx>
>
>
> ________________________________________________________________________
> ________________________________________________________________________
>
> Message: 1
>    Date: Wed, 22 Nov 2000 15:20:19 -0200
>    From: lunazzi <lunazzi@xxxxxxxxxxxxxx>
> Subject: Re: holographic 3d
>
> Peter Homer wrote:
>
> > >The technique of projecting with mirrors is as old as 4000 years (the
Incas and
> > >the Olmecas). I did not think these new world civilisations were as old
as this
> > which is as old or older than anything in the old world and I thought
the Olmecs were the oldest rather than the Incas
>
> I do not know if they were older than the Incas, the interesting thing is
that they disappeared before the Aztecs but left a very important influence
on them. I do not know if Teotihuacan is considered precisely Olmec, but it
seems to be, and was considered as a sacred city when it was found inhabited
by the Aztecs.
>
> > but perhaps that was just in Central rather than South America
> > >http://www.geocities.com/Athens/Forum/3853/olm1e.html
> > >
> > I had a look at this site although I could not view the graphics
properly with my my Netscaoe Navigator 2.02,
>
> Maybe it is due to the version, because I use Netscape 4 now, although I
started with 2.0
> I verified by reading from a different terminal than I used for  editing,
to avoid the direct lecture on the computer rather than through internet (is
a typical error that sometimes arrives to me).
>
> > I found it very interesting but was the original intention of the
concave mirrors to project images or to focuss the suns rays to produce
fire,as the name Tezcatlipoca ( smoking Mirror) suggests. Perhaps with a
religious significance as the fire was taken directly from the sun,
>
> This was already made by the Incas, precisely as you wrote, but using
metal mirrors.
>
> > I have seen some other illustrations of these types of mirrors made from
polished pyrite or iron sulphide FeS2 which can form naturaly in balls or
discs
>
> I have some samples, but not in the form of balls or discs.
>
> > consisting of radiating needle like crystals. Specular haematite can
also form a miror like surface when polished,
> >
>
> I am trying a technician to made the polishing on them, using aluminum
oxide.
>
> I would like to put more information on my page, including the whole
article, but for the moment I can mail you the article if you send me your
postal address.
>
> > >Projecting on lenses is also interesting, it renders a floating image.
> > >The progress in this last years shoul be in increasing the field of
view, wether
> > >using paraboloidal mirrors more specific that the Olmecas ones (as
Peter Homer
> > >indicated)
> >
> > P.J.Homer
>
> The serpent heads emerging in the Teotihuacan temples (pyramides) arises
from mirrors (archeologist said), what shows clearly (at least to me) that
mirrors were employed for imaging.  On the other hand, if they were merely
to concentrate sun,  I can suppose that it did not needed so much polishing.
Another interesting feature is that most Olmec mirrors has two different
focal lenghts (along perpendicular directions) what makes them to not
concentrate light in focus.
>
> José
>
>
>
> ________________________________________________________________________
> ________________________________________________________________________
>
> Message: 2
>    Date: Wed, 22 Nov 2000 23:31:39 -0600
>    From: "Michael K. Davis" <zilch0@xxxxxxxxxxxx>
> Subject: Re: Stereo Base Calculation with a $20.00 Handheld
>
> Abram,
>
>
> >Date: Mon, 20 Nov 2000 15:52:01 -0000
> >From: "Abram Klooswyk" <abram.klooswyk@xxxxxx>
> >Subject: Re: Stereo Base Calculation With a $20.00 Handheld
>
> [snip]
>
> >Michael Davis wonders why I call the so-called "General Solution"
> >paradoxical.
> >The formula is for base calculation, to get a base which results in
> >a viewable deviation. Many newbies like such a rule. However, the
> >formula next asks for an _input_ of the deviation which it should
> >provide as _outcome_ on film, after _using_ the calculated base.
> >Newbies will ask: what deviation?
> >You can calculate it from the base, and than get in an endless
> >regression. In discussions many different values for deviation are
> >mentioned, which isn't particular helpful for newbies.
>
> There is no paradox.  You could apply your argument to the push-pull
> relationship between aperture and shutter speed.  But unlike the
> relationship between aperture and shutter speed, where we quite often
> toggle between wanting to fix one and solve for the other, any hope of
> calling the General Solution a parodox vanishes when we acknowledge that
> Base is on one side of the equal sign, ALL BY ITSELF, and deviation is one
> of several variables on the other side.
>
> The General Solution is an equation.  The author had a reasonable
> expectation that users would understand they are *solving for base*, NOT
> solving for deviation, not solving for focal length, not solving for near
> point or far point, etc.  I have yet to see the General Solution expressed
> as a solution for deviation - with a  d  all by itself on one side of the
> equal sign and base specified as a variable along with all the others, on
> the other side of the equation.
>
> I can't imagine any newbies actually doing the math to rearrange the
> General Solution in the first place, much less finding themselves in an
> endless regression, solving for deviation, then for base, then for
> deviation, then for base, etc.  Your argument is quite simply fantastic.
>
> Everyone I've read about or spoken to who uses the General Solution, is
> completely content to use it for one purpose - solving for base.  Base is
> the output.
>
> The formula is used to deliver a base value that will PRODUCE the on-film
> deviation you have CHOSEN to specify as a variable.  The General Solution
> can deliver numerous bases, each unique to the scene described by the Near
> and Far variables, but these bases, though different from one scene to the
> next will CONSISTENTLY produce the CHOSEN on-film deviation, within the
> range of bases permitted by your equipment and technique, of course.
>
> It is not at all difficult to select an on-film deviation value that
> satisfies your personal taste for how much depth your images will have.
>
> My original post, as seen at
>
> http://www.pauck.de/archive/mailinglist/tech-3d/mhonarc/msg01919.html
>
> suggests shooting with bases that are calculated using a deviation equal
to
> 80% of the Maximum Allowable On-Film Deviation.  I also explained that
> MAOFD is just the camera focal length divided by 30.   80% of MAOFD is
just
> a place to start.  Shoot a few rolls at 80% of MAOFD to get a feel for it.
> It's subjective.  It's up to you to determine if you find it appealing.
If
> 80% of MAOFD is a little too strong for you (too much "bite" for your
> taste), try a few rolls at a lesser percentage.  The General Solution will
> deliver the exact same deviation on-film, every time.  And even if you've
> found that something like 75% MAOFD suits your needs most of the time,
> there's nothing stopping you from CHOOSING more or less depth for a
> particular scene you are about to shoot.  You are in control, but it's
your
> responsibility to get a feel for the numbers.
>
> [snip]
>
> >When you want to emphasize tiny scratches on ancient coins, stretch
> >might be your purpose. But Michael Davis says:
>
> >>It is my personal preference to use a variable base,
> >>following the General Solution, for nearly every situation,
> >>including the mid-field.
>
> >When this would include a portrait of a person before a nearby
> >"backdrop" I'm afraid I would call it weird, to say the least... :-).
>
>
> It is apparent that your intention here is to suggest that in a situation
> where stretch might be desirable, I would use the General Solution and
this
> would somehow prohibit that goal.  This assertion is incorrect on two
> counts.  First, using the General Solution, I can add stretch at will by
> increasing the deviation used to calculation base.  The General Solution
> does NOT have to be calculated using the Maximum Allowable OFD or any
other
> fixed value for deviation.  Second, the article from which you quote
> clearly states that I abandon the General Solution at Near:Far ratios less
> than 1:2.  I discuss that at length across several paragraphs. (See the
> link above.) Did you miss that portion of my article or are you just
> spinning my words?
>
> I will vigorously defend your right to prefer more or less on-film
> deviation than I do.  I will support your right to select and use
equipment
> and methodology that YOU find satisfying.  But I can not refrain from an
> equally vigorous defense against absurd attacks on the truth embodied by
> the General Solution.  The formula matches the geometry perfectly.  It is
> both valid and useful.
>
> Why must there be a steady onslaught of condemnation for something so
> unambigous?   I'm convinced it's mostly just a matter of:
>
> ignorance (I don't know how to use it so I hate it.)
> arrogance (My many years experience have canonized my techniques.)
> pride (I will never admit I'm wrong about other people's techniques.)
> laziness (I'll just burn a lot of film and see what I get.)
> contentiousness (I live to stomp on other people.)
>
> or some combination of the above.
>
> Mike Davis
>
>
>
> ________________________________________________________________________
> ________________________________________________________________________
>
> Message: 3
>    Date: Wed, 22 Nov 2000 23:58:50 -0600
>    From: "Michael K. Davis" <zilch0@xxxxxxxxxxxx>
> Subject: Why consider ratio of Viwer FL to Camera FL?
>
> Hi Boris,
>
> >Date: Mon, 20 Nov 2000 17:33:48 -0500
> >From: boris@xxxxxxxxxxxx
> >Subject: Re: Stereo Base Calculation With a $20.00 Handheld
>
> [snip]
>
> >I have a question.  Why does a viewing device focal length (i.e. a
viewing
> >geometry) even come into play?  On film deviation is the product simply
of
> >camera optics, stereobase, and near and far point.  Why the viewer F.L.?
> >Granted, the viewer optics affect the perceived depth, but it certainly
> >does not change OFD.
> >
> >(And for my application, in shooting for anaglyphs, there is no viewer
F.L.
> >There may be a print size, and a viewer's naked eye distance to print -
> >that would form the equivalent to a viewer's focal length.  But to shoot
> >for a specific size anaglyph print, and therein a specific deviation on
> >paper, I want to predict and set up a shot simply for a particular
> >deviation on film.  Viewer optics are not otherwise considered.)
> >
> >Boris
>
> If you already know an on-film deviation that gives you the look you like,
> using whatever display mechanism you employ, then you need not be
concerned
> about compensating a mismatch between viewer focal length and camera focal
> length.
>
> I include this ratio of vFL to cFL as a factor in calculating base because
> just as sitting in the front row of a 3D theater causes squash not
> experienced in the middle row, my camera lenses, being of shorter focal
> length than my viewer lenses cause that same squash.  Increasing the base
> proportionately compensates this.
>
> I have a closeup 2D picture of my dog's face shot with an 18mm lens (on a
> 35mm body).  His nose is nearly the width of his forehead.  Viewed at a
> distance of ten feet, he looks comical in this picture.  But if you view
> the print at a distance equal to the camera focal length times the
> enlargement factor, (about 8 inches for this 11x14 print), his proportions
> appear to be normal.
>
> Mike
>
>
>
> ________________________________________________________________________
> ________________________________________________________________________
>
> Message: 4
>    Date: Thu, 23 Nov 2000 08:04:25 -0500
>    From: Andres Posada O <aposadao@xxxxxxxxxx>
> Subject: Re: Re: Stereo Base Calculation with a $20.00 Handheld
>
>
>
> "Michael K. Davis" wrote:
> >
> >
> > The General Solution is an equation.  The author had a reasonable
> > expectation that users would understand they are *solving for base*, NOT
> > solving for deviation, not solving for focal length, not solving for
near
> > point or far point, etc.
> >
> > Everyone I've read about or spoken to who uses the General Solution, is
> > completely content to use it for one purpose - solving for base.  Base
is
> > the output.
> >
>
> Michael:
>    In my HP48G+ I can solve for what ever I want (anybody with the
> formulas in a computer or the like may obviopusly do it). Doing 3D video
> I am usually stuck to minimum camera separations, dictated by the camera
> sizes, that require that I solve for near point, sometimes I need to
> solve for far point. For example: if I have a minumum camera separation
> due to camera size of say 165mm, and the nearest object is going to be
> at 3000mm, then how far may the farthest object be, all this subjected
> to a MOFD choosen according to CCD size, lens focal length and TASTE.
> What happens to the near point if I change the focal length position in
> the cameras zoom lenses? Everything changes if I use 1/3", 1/2", or 3/4"
> CCDs cameras. MOFD numbers I change according obviously to CCD size, but
> also I use more "liberal" numbers if all subjects are inside the window,
> be more conservative with subjects way out of the window and near to the
> camera. My point is I almost never solve for base.
>
>
> ________________________________________________________________________
> ________________________________________________________________________
>
>
>
>


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