Canon Camera Hackers Manual page 232

Focus ref distance. The distance of the virtual image projected by the
f
telescope lens and the subject distance to which the camera will focus.
500 mm is a good starting point.
After you have entered these values, you can review them in Record mode
using the DOF browser (ALT+LEFT/RIGHT).
Scope mag. The magnification of the scope.
f
Scope EP. Diameter of the scope's exit pupil in mm. This entry will be red
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when it is the limiting aperture (smaller than the camera's entrance
pupil).
Camera EP. The diameter of the camera's entrance pupil in mm. This
f
entry will be red when it is the limiting aperture (smaller than the
scope's exit pupil).
EFL. The combined focal length of camera and scope.
f
EFL (35mm). The 35mm-equivalent of EFL.
f
It's a good idea to use focus bracketing in connection with digiscoping.
First, it increases the tolerance for focusing. Also, the series of images ob-
tained can be combined via focus stacking (section 4.6.3) in order to in-
crease the depth of field. With digiscoping, the DOF is notoriously small, so
focus stacking can make a lot of sense.
In the Brackt/Override submenu, set Focus mode to Digiscop. This will
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cause bracketing around the preset Focus ref distance. The step size will
also depend on this value: the lower the Focus ref distance, the smaller
the focus step size.
Set Tv bracket value to Off.
f
Choose any value from 3 times to 19 times in entry Bracketing type.
f
Exit <Alt> mode and set the camera to Continuous mode or to Custom
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timer (with an appropriate number of shots).
Of course, the scope must be mounted on a sturdy tripod. The camera must
be mounted on the same tripod, so you need some kind of a bracket (digi-
scoping adapter) on which both scope and camera can be mounted and
adjusted. The ideal adapter would allow swinging the camera quickly out
of place (for access to the ocular) and swinging it back again without com-
promising stability. Such adapters are not cheap—they may even cost more
than your camera. For the occasional shot, however, this low-cost and low-
tech version may be an alternative:
www.videojug.com/webvideo/how-tomake-a-digiscoping-adapter.
You also need to trigger the camera with the help of a USB remote
control. Because the Digiscop focusing mode switches the camera to FAST
mode, the camera will fire immediately when you press the switch instead
of waiting for switch release. If you don't have a remote cable, you could
7.8 Digiscoping
Figure 7-14
The DOF browser showing the
Digiscope Data. The entry Camera EP
is colored red, indicating that the
camera's entrance pupil (Camera EP)
is the limiting aperture. In the ideal
case, it will match the Scope EP.
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