Re: [photo-3d] Re: DOF & Rangefinder

["Don Lopp" <dlopp@xxxxxxxxxxxxxxx>]

Chuck,Chuck Holzner-I hasve never seen a slide film capable of resolving 60
lines per mm DON
----- Original Message -----
From: "Chuck Holzner" <cfholzner@xxxxxxxx>
To: <photo-3d@xxxxxxxxxxx>
Sent: Friday, January 05, 2001 3:17 PM
Subject: [photo-3d] Re: DOF & Rangefinder


> > For every f-stop there is a distance associated with it,
> > called the hyperfocal distance.  This gives the maximum DOF for
> > this given f-stop.  If you focus at the hyperfocal distance for the
> > given f-stop then your Depth of Field (DOF) extends from half
> > that distance to infinity.  People who focus at the hyperfocal
> > distance do not necessarily use the "tightest" i.e. smallest f-stop.
> > But they want to have infinity in focus and as much in the
> foreground
> > in focus as possible.
>
> The way to get infinity in sharpest focus is to set the focus to
> infinity.  Anywhere else will degrade the sharpness at infinity.  The
> depth of field range is not where everything is in sharp focus.  It
> is a range where it was decided the focus is acceptable (by whom I do
> not know).  The standard DOF range on the 35 MM stereo cameras seems
> to be about equal to 30 lines per MM on the film.  This is just fine
> if you only plan to view your slides by projection as most projector
> screen combos can't do this good.  60 lines per MM is what I feel is
> desireable and I use fine film and a good viewer.  To get 60 lpmm in
> your DOF you must use a range at least 2 F stops tighter then the
> markings on your Realist.  That means for F16 use F8 markings.
>
> >
> > >I use a rangefinder AND DOF.  With the rangefinder, I measure the
> distance
> > >to the nearest object I want in focus.  I then measure the
> distance to the
> > >farthest object, then set the camera focus between the near and
> far distance
> > >with the two distances at similar F stop markings on the DOF
> scale. This
> > >gives the same sharpness at near and far with everything in
> between sharper.
> >
> > Fair enough.  Does it matter what is this "similar F stop markings
> on
> > the DOF scale"?
>
> No it doesn't.  I am centering the focus for best sharpness over the
> range.  The markings will be different for different ranges.
> >
> > >I then select the F stop based on light, lens sharpness, and DOF.
> Mostly I
> > >use F11 or F16.
> >
> > You went to this trouble to use f11 or f16?
>
> No big trouble, I just want to do my part making the picture as best
> I can.
>
> If you look up the
> > hyperfocal distances for f11 and f16 for the Realist, etc., you
> > will see that focusing at the hyperfocal distance for either of
> > these f-stops will give you plenty of DOF to have everything
> > sharp in the picture.
>
> We are back to the definition of sharp.  Yours is 30 lpmm,  mine is
> as sharp as I can make it.
>
> >
> > >It is easier if I have infinity or very far objects in the
> picture.  I use
> > >the rangefinder to measure the distance to the nearest object and
> then set
> > >the focus to twice that range.  This is the principal behind the
> hyperfocal
> > >table in the older Realists.
> >
> > No, it's not.  If you use a relatively wide aperture and you have
> > to have infinity in focus then focusing at twice the distances of
> > the nearest object will not necessarily give you a sharp infinity.
> >
>
> Yes it is.  Infinity will have the same sharpness as the nearest
> object; check you DOF scale against the hyperfocal table.
> If you need more DOF, stop down and increase shutter time.  Both near
> and far will be in the same degree of focus.
>
>
> > If you are going to use f11 and f16 in the Stereo Realist then
> > you don't really need to know the distances of the near and
> > far objects with any degree of accuracy.
>
> I disagree again.  What you "need" and what you "want" are not always
> the same and you should know the distances with "some" degree of
> accuracy.  If everything in my picture is beyond 15 feet and I am
> using F16,  I an not going to use the Hyperfocal distance of 8 feet
> (out of my Realist cap) for the shot.  Using my method I would set
> focus at 30 feet and Infinity would be sharper and the near object
> just as sharp.
>
> >
>
> > The bottom line is this:  Your method is good but for the
> > majority of the photographic situations with the Stereo Realist
> > you do not need to know the distances of the near and far
> > objects with high degree of accuracy.  Knowing what the
> > hyperfocal distance is and how it works, will simplify
> > life for many individuals in many situations.
>
> So will buying a fixed focus camera.  Not for me, thanks.
>
> Why does the Realist have a rangefinder if you don't need it?
>
> You don't have to answer that, I know the Realist 45 doesn't have one.
>
> Chuck
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