D850
Focus Shift Ⅰ, the Basics: Stacking Focus
Narration: YAMANO Yasuteru
Focus Shift: What It Does and How to Enjoy It
The D850’s handy “focus shift” feature is used
chiefly to create the raw materials for focus stacking.
Focus stacking
is a means enhancing depth of field by taking a series of shots and generating a composite
image consisting only of the areas that are in focus. Although dedicated focus-stacking
software has been around for a while, the hard part was getting suitable high-quality
raw material.
Specifically, what was difficult was taking a series of photos
while changing focus a small, fixed amount with each shot. It used to be hard to change
focus by the same amount with each shot, and unless you finished shooting quickly,
there was a chance that the light would change or some other difficulty might arise,
resulting in photos that were not suitable for focus stacking. This is precisely the
sort of difficulty the D850’s “focus shift” feature, which automatically
varies focus by a set amount over a set number of shots, was introduced to solve.
When it comes to focus stacking, it might seem natural to ask, ‘Why
go to all that trouble when you can just stop aperture all the way down?’ but
it’s not that simple. Given the same aperture and a lens focal length chosen
to produce the same picture angle, the large image sensors in FX format cameras and
the like will show a shallower depth of field than smaller sensors, so you really
have to stop aperture down to get a deep depth of field. And stopping aperture down
increases diffraction, resulting in pictures that lack definition.
In these
circumstances, the way to get good depth of field without stopping aperture down so
far that pictures lose definition is focus stacking. I think the ability to produce
high-definition prints with deep field depths at sizes of B0 or larger will be celebrated
not only by photographers who want highly detailed shots of insects and other traditional
focus-stacking subjects but also by landscape photographers shooting commercial photos
or works they plan to exhibit.
Adjusting Settings
Overview
To adjust focus shift settings, go to the photo shooting menu and
select Focus shift shooting. The options available include No.
[number] of shots, Focus step width, Interval until
next shot, Exposure smoothing, Silent photography,
and Starting storage folder (with sub-options New folder
and Reset file numbering), but the ones with the greatest influence
on how focus stacking turns out are Focus step width and No.
of shots. And although they aren’t in the menu, other important factors
are aperture and the starting focus position. We’ll take a look at each of these
in turn.
Aperture
Because we don’t need to worry about getting a deep depth of field
with a single photo, we can instead consider how aperture can be adjusted to produce
a high-resolution, high-definition image with each shot. Specifically, we need to
think about the aperture at which the lens performs best. If diffraction were our
focus, it could be minimized by shooting at maximum aperture, but, given the characteristics
of the lens, a setting two to three stops lower, say f/2.8 to f/8, is in fact generally
best if we also want to keep the definition image high right up to the edges.
Starting
Focus Position
In focus shift, the camera takes a series of shots
starting from a selected focus position and continuing toward infinity. We will therefore
choose a starting focus position either at or slightly in front of the closest point
of the section of the subject that is in the desired depth of field.
Personally,
I focus on the closest point on the subject visible in the frame and then slightly
reduce the focus distance before I start shooting.
Focus Step
Width
You have a choice of ten focus step widths, ranging in value
from 1 to 10. The amount the focus distance changes with each shot is not determined
solely by the focus step width but is calculated by the camera based on a variety
of lens data, including focal length and aperture, so it’s probably best to
experiment until you get the hang of it.
The mistake people make in choosing
the focus step width is to pick one so large that some areas in the focus-stacked
image are out of focus. To prevent this, a focus step width of 5 or less seems safe.
Focus shift photography itself is very easy and there is no need to worry
about taking too many shots, so I generally choose a focus step width of 2 or 3 for
images I want to print at a large size.
Number of Shots
The number of shots can be set to values between 1 and 300. Speaking from
experience, you’ll generally need over a hundred shots to cover the desired
field depth when photographing an insect or other small object using macro photography
at the settings described above, namely an aperture of f/5.6 and a focus step width
of 2 or 3. On the other hand, to cover a landscape starting close to the camera and
extending into the distance, you need only take a few shots, particularly if you are
using a wide-angle lens, as the depth of field of each of the individual photos will
already be quite deep.
The D850’s focus shift function includes a
feature that automatically ends shooting when the focus distance, which increases
with each shot beginning from the starting focus position, reaches infinity, so you
needn’t worry that it’ll take a bunch of photos you don’t need after
infinity is reached. It can be tricky to choose the minimum number of shots needed
based on the lens focal length or focus step width, but you can take some of the pressure
off during shooting by taking a large number of photos with the idea that you can
choose the ones you want during focus stacking.
Other
Settings: Interval Between Shots, Exposure Smoothing, Silent Photography, and Starting
Storage Folder
Starting with the interval between shots,
“zero” is basically a good choice. With the interval set to zero, the
camera starts shooting the next photo as soon as the previous one is finished, meaning
that the focus-shift series can be completed in the minimum amount of time. Longer
intervals are only needed to force the camera to wait when, for example, each photo
uses the flash and you need enough time between shots for the flash to charge. Zero
can be considered the best choice in all other cases.
Exposure
smoothing adjusts exposure to smooth out changes in subject brightness that
may occur during shooting, but really you want all the photos in a focus stacking
sequence to be shot under the same lighting and other conditions in the shortest possible
period of time. The default setting of “Off” is recommended in most situations,
but you can choose “On” if you have no choice but to shoot under changing
light conditions.
When using focus shift, you’ll mostly be photographing
stationary subjects with the camera on a tripod, and you can either choose silent
photography or shoot with the regular mechanical shutter. Personally, I prefer
silent photography except in situations in which the camera must be audible, partly
because it means I don’t have to worry about wear on camera mechanisms such
as the mirror and shutter.
The Starting storage folder
menu contains two options: New folder and Reset file numbering.
Performing focus stacking after shooting is easier if all the photos in each focus
shift series are in the same place, so it’s probably best to select New folder
and reset file numbering to 1.
The exploration continues in “Focus
Shift Ⅱ: Focus Stacking”.
Tips and Tricks > Focus Shift Ⅱ: Focus Stacking
Profile of YAMANO Yasuteru
Photographer and researcher of photographic techniques. Born in 1954 in Kagawa. Has been publishing photos and articles in astronomical journals since the 1970s. Has published many digital photos and articles relating to digital astronomical photography since the year 2000. Member of the Society of Photography and Imaging of Japan (SPIJ).
Model cooperation: KATO Co., Ltd.
Diorama cooperation: atorie-minamo
Equipment cooperation: Kenko Tokina Co., Ltd. SLIK Light carbon E83 FA