[photo-3d] Re: DOF & Rangefinder

["Chuck Holzner" <cfholzner@xxxxxxxx>]

> 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