The Art of Focus Stacking - Matrix Software

Equipment for Macro and Close-up Photography
The Quest for Depth of Field
As long as there have been cameras and lenses, photographers
have struggled to achieve greater depth of
field (DOF). When a lens is wide open the DOF is very
shallow, which means that, at best, you can expect to
have sharp focus only in one plane of the photo. The
rest of the frame will be more or less out of focus.
As we close down the lens (smaller openings), we
achieve greater and greater DOF until a point is
reached where the effects of diffraction set in and
begin to destroy the overall sharpness of the photo.
So photographers are caught between the devil and
the deep blue sea, trapped by almost no DOF at wide
apertures or loss of sharpness when stopped down
too far. That has been the traditional problem.
We all seem to like to see photos that embrace greater
DOF and with the advent of focus stacking this is
becoming increasingly possible. Focus stacking has
been going on for a long time, but limited to those
photographers with enough technical expertise in Photoshop
(or other software) to painstaking stack layers
of photos and then gradually erase part of different
layers to reveal those areas of greatest sharpness.
Each photo becomes a real labor of love and is very
time intensive.
Now that Photoshop CS4 (and other software) can do
this more automatically, focus stacking is increasing
coming into its own. Today (using Photoshop as an
example), all that is necessary is to place the stack
of photos (at different focus points) as individual layers
and apply two commands to that stack, Align and
Blend.
The “Align” command automatically works through the
layers and aligns the subject in each layer so they line
up. Once that is done, the “Blend” command blends
the aligned layers into a single photo, automatically
doing what previous photographers laboriously did
by hand. The resulting image is a stacked photo,
where the stack of individual photos has been aligned,
blended, and reduced to a single photo that appears
to have a greater depth of field or overall sharpness, if
all has been done correctly.
Users of Adobe Lightroom 2.0 (and higher) can select
a series of photos in Lightroom and send them to
Photoshop where they can be aligned, blended, and
automatically saved back into Lightroom, including
any adjustments made to the photos in Lightroom.
What this means is that focus stacking is now available
to a much wider group of users than in the past.
Just as HDR-stitched photos have become very popular
and have their own special “look,” we can expect
to see focus stacking following on the same path to
more common usage. Focus stacking also has a certain
look that differentiates it from standard photos.
Perhaps camera makers like Nikon may include focus
stacking (focus bracketing) in future camera bodies
just like they did with aperture bracketing, which
is now available. The user would focus at the front
and the rear of a subject, indicate how many photos
should be stacked, and the camera would do the rest.
Of course, this sounds like a job that would require
a tripod. For shots of live subjects, in-camera focus
stacking would further open up this technique, since
the stacked series would happen at maximum speed.
Later in this text, we will walk through how to use
Adobe Photoshop to stack photos.
Diffraction
When you camera lens is wide open like F/2.8, there
is plenty of room for light to enter and the parallel
rays of light more or less stay parallel, with minimal
divergence. However when you narrow the lens to a
tiny opening, like f/22, not only does less light come
through, but after passing through a small aperture,
parallel light rays begin to diverge, spread out, and
interfere with one another.
At small apertures the light waves get out of phase
with one another, pile up in some areas, and cancel
each other out in other areas. The net result is that
they create a pattern of bands called the “diffraction
pattern,” and this pattern impacts the photo image we
are trying to create, causing it to deteriorate.
The long and the short of it is that no matter how
fine a lens you have or how many megapixels your
camera sensor has, diffraction imposes an absolute
resolution limit for photo detail that cannot be gone
beyond. Diffraction automatically smoothes or blurs
detail that we have resolved with the higher f/stop of
the lens.
Web Sites for Lenses
The best web sites to learn the qualities of lenses (in
my opinion) are:
Bjørn Rørslett (http://www.naturfotograf.com)
Thom Hogan (http://www.bythom.com)
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