14
z
Taking Hemiphotos
SLM6 User Manual v 1
button, change lenses with the command dial.
Use of the Normal lens setting and its default zoom position is OK,
but it wastes some resolution because the image will be smaller than
it needs to be.
•
Focus
Auto, Single AF
•
Zoom
Digital Tele Off
See notes above about zoom lens
•
Speedlight cntrl
Int & Ext Active
•
Flash Exp Comp -2.0EV to reduce flash brightness.
Set the flash to “Anytime Flash” (Fill Flash) using the flash button, see
Camera Manual p 38.
These settings can be saved in one of the user settings so they can be
easily restored, see Camera Manual p 98.
Exposure
Getting the exposure right can have a significant effect on how easy it is to
classify your image in HemiView, and on the accuracy of your calculations.
Your aim is to have areas of sky at the top end of the brightness range,
and areas of canopy at the lower end. You can check this on your image
by looking at the brightness graph (Camera Manual p 5 & 69).
If the image is overexposed, the sky areas will have a tendency to spread
in the final image. Underexposure is less of a problem, but will reduce the
amount of visual detail of the canopy. The camera’s automatic exposure
will tend to adjust the exposure too much for very open and very closed
canopies. We suggest two approaches to dealing with this.
1 Manual Exposure
•
With the camera in Programmed Auto exposure mode (Camera
Manual p 45), note the exposure values under a section of canopy
with about 50% sky visible. Use the command dial to select the
highest f-number consistent with a shutter speed faster than 1/60
second. This is to minimise camera shake, but use the smallest
aperture possible to give the greatest depth of field in focus.
•
Set the camera to manual exposure, and set the shutter speed and
aperture to these values.
•
Use this exposure setting for all your hemiphotos, as long as lighting
conditions remain the same. The exposure meter will indicate over-
exposure for open canopy, and under-exposure in closed canopies.
