[MF3D.FORUM:1700] Re: Using front shift to simulate camera movements?

["Don Lopp" <dlopp@xxxxxxxxxxxxxxx>]

It appears obvious to me that I missed the point at issue AND erroniously
assumed the issue  was using mirrors to control the interocular spacing
using 4x5  camera or cameras Apparently my goof DON
----- Original Message -----
From: "Tom Hubin" <thubin@xxxxxxxxx>
To: "Medium Format 3D Photography" <MF3D.Forum@xxxxxxxxxxxxx>
Sent: Thursday, April 12, 2001 11:44 PM
Subject: [MF3D.FORUM:1684] Re: Using front shift to simulate camera
movements?


> Hello Don,
>
> The field of view limits are determined by the camera itself. In
> particular, by the film size and the lens focal length. The amount of
> light is controlled by the lens fNumber. No reason to loose any of the
> field of view or light just because you use a mirror.
>
> If you use too small a mirror then it acts like a rectangular aperture
> placed near your lens. No loss in field of view but some light will be
> lost just like increasing your fNumber. This may show up as vignetting.
> If extreme is may cut into your field of view.
>
> Lets draw a top view picture. Use graph paper if possible.
>
> Draw the two camera lenses as you would without mirrors. These are
> cameras without bodies so we can put them as close as we want to each
> other as long as the lenses do not overlap. Draw the lenses as thin
> lenses with just simple lines. Side by side. Correct diameter. Correct
> interocular.
>
> Now draw the film, as a thin line, the correct horizontal size.
>
> Now draw field of view lines from the edges of each film through the
> center of the corresponding lens. Extend the lines beyond the lenses as
> far as you like (too the edge of the paper is fine). These large Xs
> define your angular field of view. If this were a pinhole camera we
> would be finished.
>
> To avoid vignetting you need to evaluate the sides of the lenses as well
> as the center. So from the extremes of each lens draw lines away from
> the camera and parallel to the pair passing through the centers of the
> lenses.
>
> You now have a sketch of all of the light that can travel from a subject
> at infinity, through a lens, and onto the film. Very close to the camera
> lenses there is no overlap of the light paths because the lenses
> themselves do not overlap. Some distance away from the camera lenses the
> right path and the left path do overlap. Any apertures or mirrors in the
> area where they overlap will be a problem of some sort. This cross point
> is as far away as you can place the farthest (common) edge of the
> mirrors. Farther away from the camera lenses than this cross point will
> cause losses in light (vignetting) and possibly field of view if way
> beyond this point.
>
> However, between that crossing point and the lenses you can impose the
> right size mirrors with impunity.
>
> Now here is a trick of the trade. Cut out the outline of your drawing.
> There will be a V formed by the cutout of the triangle between the
> lenses and the crossing point. Now fold each path at 45 degrees so that
> the lenses are at right angles to the way you started. In particular,
> fold the paper about where you would like to place the mirrors.
>
> Now the figure looks like what you had in mind. The creases where you
> folded the paper ARE the mirrors. As long as the mirrors are long enough
> to cover all of the rays you loose nothing.
>
> You may sometimes here mirrors like this referred to as folding mirrors.
> Now you know why.
>
> You may be able to do a second fold in each path. This would then
> produce normal images rather than mirrored images.
>
> Also, do not limit your folding to 2 dimensions. You can fold lots of
> ways. Both up or one up and one down or whatever. Or at angles other
> than 90 degrees with 45 degree mirrors.
>
> Give me some realistic numbers for lens focal length, lowest fNumber for
> that lens, film width and I will come up with mirror size and location
> that should work with no losses.
>
> I think I have Power Point and Word here, although I have seldom used
> either. Would a sketch in Power Point help? Would copying that sketch
> into Word be better? Would it be useful to have such a sketch on
> somebody's website?
>
> Tom Hubin
> thubin@xxxxxxxxx
>
> ******************************
>
> Don Lopp wrote:
> >
> > Tom . if I am wrong ,please tell me wh at angle of field I can expect t
be
> > able to utilize . i do not epect it to be very much by normal stereo
> > standards by which I do not consioder View Master a decent standard.
DON.
> > ----- Original Message -----
> > From: "Tom Hubin" <thubin@xxxxxxxxx>
> > To: "Medium Format 3D Photography" <MF3D.Forum@xxxxxxxxxxxxx>
> > Sent: Tuesday, April 10, 2001 8:40 AM
> > Subject: [MF3D.FORUM:1664] Re: Using front shift to simulate camera
> > movements?
> >
> > > Hello Don,
> > >
> > > Not true. It depends entirely on how you do it. If you connect all
> > > points on the subject to all points on the lens and the mirror
> > > intersects all of those rays then you loose nothing.
> > >
> > > For stereo there is a practical limit on this single mirror approach.
> > > The system is creating the illusion that the lenses are side by side
> > > with the camera bodies overlapping. They cannot appear closer than
> > > touching each other without clipping something. For example, if the
> > > lenses are 50mm diameter then 50mm is the smallest interocular that
you
> > > can create without clipping.
> > >
> > > To avoid clipping at 45 degrees you need a mirror that is the square
> > > root of 2 larger in the folded dimension. So a minimum of 50mm by 71mm
> > > ellipse would be needed in the above example.
> > >
> > > Tom Hubin
> > > thubin@xxxxxxxxx
> > >
> > > **************************************
> > >
> > > Don Lopp wrote:
> > > >
> > > > Plus the angle covered would be relatively narrow DON
> > >
> > > > ----- Original Message -----
> > > > From: "Bill Glickman" <bglick@xxxxxxxx>
> > > > To: "Medium Format 3D Photography" <MF3D.Forum@xxxxxxxxxxxxx>
> > > > Sent: Wednesday, April 11, 2001 12:31 AM
> > > > Subject: [MF3D.FORUM:1657] Re: Using front shift to simulate camera
> > > > movements?
> > > >
> > > > > Tom
> > > > >
> > > > >         I'm not understanding this....  If you look forward you
see an
> > > > > image, if you turn 90 deg and use one mirror at 45 deg, you will
see
> > the
> > > > > same image.  So why wouldn't the film see the same thing looking
in
> > the
> > > > > mirror?  Are you sure you would have to view the slide with the
> > emulsion
> > > > > side away from our eyes to get the same effect as if the cameras
shot
> > > > > straight at the scene?  Hmmmm..if so, that does not sound good,
but
> > then
> > > > > again we look straight through the slides anyway?
> > > > >
> > > > > Bill g
> > > > >
> > > > > > Clever idea but the images will be mirrored. So you will need to
> > print
> > > > > > with the emulsion side up or view slides with the emulsion side
away
> > > > > > from the eye or project with the emulsion side away from the
screen.
> > > > > > This will reduce the quality of the image.
> > > > > >
> > > > > > A pair (or any even number) of mirrors for each camera is more
> > > > > > complicated but would avoid the mirror image problem. For that
> > matter,
> > > > > > two mirrors on one camera and no mirrors on the other camera
would
> > also
> > > > > > work. But then the distance from camera lens to subject is not
the
> > same
> > > > > > for both cameras.
> > > > > >
> > > > > > Tom Hubin
> > > > > > thubin@xxxxxxxxx
> > > > > >
> > > > > > **********************************
> > > > > >
> > > > > > Matthew V. Ellsworth wrote:
> > > > > > >
> > > > > > > Bill
> > > > > > > I'm not sure if I'm understanding what you want to do, but
maybe
> > this
> > > > > idea will
> > > > > > > help:
> > > > > > > Two cameras can be mounted facing each other on an adjustable
> > rail --
> > > > > with a
> > > > > > > small front-surface mirror mounted at a 45 degree angle in
front
> > of
> > > > each
> > > > > lens.
> > > > > > > This allows you to get both cameras quite close (limited by
the
> > size
> > > > of
> > > > > the
> > > > > > > mirrors), and allows easy access to the focusing and film
advance
> > > > > mechanisms.
> > > > > > > Matt
> > > > > > >
> > > > > > > Bill Glickman wrote:
> > > > > > >
> > > > > > > >       I am trying to develop a MF camera system that allows
one
> > to
> > > > set
> > > > > > > > interocular bases at any seperation without physical
> > > > > limitations.....As we
> > > > > > > > all know, this is physcially impossible sometimes with two
non-
> > > > shift
> > > > > > > > cameras.  My idea was to use two cameras side by side, but
each
> > one
> > > > > would
> > > > > > > > have the capability to shift the lens horizontally.   This
has a
> > > > very
> > > > > > > > dramatic effect vs. spacing the cameras.  For example, I can
> > > > simulate
> > > > > 24"
> > > > > > > > interocular distance with only 3mm of front shift on one
camera.
> > I
> > > > > have
> > > > > > > > tested this, it works.  So a small amount of lens shift
would
> > > > simulate
> > > > > > > > interocular spacing fro 0 to 500 + ft.
> > > > > > > >
> > > > > > > >       I have found that myself and my audience all prefer
very
> > small
> > > > > OFD's,
> > > > > > > > say 1.3mm, hence the need for bases much tigher than any two
> > cameras
> > > > > can
> > > > > > > > every physically acheive.   A fixed stereo camera
(sputnicks)
> > don't
> > > > > appeal
> > > > > > > > to me because I want the flexibility of adjusting the
> > interocular
> > > > > distance
> > > > > > > > when required.
> > > > > > > >
> > > > > > > >         Although this sounds good in theory, I am curious if
> > this
> > > > will
> > > > > > > > produce the same stereo effect as utilizing two cameras at
the
> > > > proper
> > > > > > > > interocular distance.  I don't plan to use it for excessive
> > bases,
> > > > > only for
> > > > > > > > 24" and less.  Has anyone every tried this before?  Any
input?
> > > > > > > >
> > > > > > > > Bill G
> > > > > > >
> > > > > > > --
> > > > > > > ______ Matthew V. Ellsworth ______________________________
> > > > > > >       oakridge@xxxxxxxxxxxxx      http://www.oak-ridge.com
> > > > > >
> > > > >
> > > > >
> > >
> > >
>
>