Canon Camera Hackers Manual page 70

programs enfuse and tufuse, the free programs CombineZP and Picolay, and
also the commercial programs Helicon Focus, PhotoAcute Studio, and Zerene
Stacker can be used. Photoshop CS4 now offers focus stacking, too.
Taking the series of single photos requires a bit of planning. You must
make sure that the different DOF areas of the images overlap nicely so
that they can easily be combined into one large DOF area. Fortunately,
the CHDK offers a DOF Calculator (section 4.2.8). Switch it on by going to
ALT > MENU > OSD Parameters
DOF Calculator. To be on the safe side, enable the entry Use EXIF Subj. Dist.
(PC65), too. You will probably get a reading that is a little too short, but that
is better than a reading that is a little too long. Then put your camera on a
tripod, point the camera at the closest point of your subject, focus, and note
down the following readings:
Subject Distance (S or SD)
f
Depth of Field ( DOF)
f
Also, measure the distance to the farthest point of your subject (F). F–S is
your desired depth of field. Now you know the number of required shots. It
can be computed from the formula 2*(F–S)/DOF. For example: given a dis-
tance of 60 mm to the nearest point of your subject, a distance of 120 mm
to the farthest point of your subject, and a DOF of 12 mm, you would end
up with 2*(120–60)/12 = 10 exposures.
If you don't use manual focus to do the measurements, you may want
to switch your AF Frame to Center for precise focusing.
Now you can configure the camera. If your camera features a manual
focusing mode, switch it on. Now dial in the following values:
To enable bracketing, you must set Disable Overrides in the submenu
f
Extra Photo Operations to Off (section 4.3.1) if you had enabled the op-
tion Include AutoISO & Bracketing (in the same submenu). Do not use
Overrides for the subject distance.
Now go to ALT > MENU
f
ous Mode. Dial half of the measured DOF into the menu entry Subj.Dist.
Bracket Value. You need to set the subentry Value Factor unequal Off.
For example, if you measured a DOF of 100 mm, you could set the Value
Factor to 10 mm and the Subj.Dist.Bracket Value to 5. This would result
in a bracketing value of 50 mm.
As Bracketing Type select "+". The camera will then make exposures with
f
increasing subject distance. For example, if you start at a subject dis-
tance of 500 mm and a bracket value of 50 mm, the camera will take
exposures at 500 mm, 550 mm, 600 mm, and so on.
Then switch the camera to Continuous mode. Again, focus on the near-
f
est point of your subject. Holding the shutter button half-pressed, turn
> DOF Calculator and enabling the entry Show
> Extra Photo Operations > Bracketing in Continu-
61
4.6 Bracketing