SLM9 User Manual v1.2
Contents
13
If the image is over-exposed, the sky areas will have a tendency to spread
in the final image. Under-exposure 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
•
Select the
Tv
: Shutter Priority AE exposure mode (Camera Manual
p. 114). Set the shutter speed to, say,1/80 second to minimise camera
shake. Note the exposure values under a section of canopy with about
50% sky visible. Use the smallest aperture hole size possible (i.e.
largest f/number) 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.
•
Having decided on an exposure setting, (as in 1 above) press the <
>
button to lock the exposure. All the hemi-photos you now take will be
at the same exposure setting.
•
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.
2 Auto Exposure
•
Set the camera to Program AE (Auto Exposure) mode
P
.
•
For more open canopies, over-expose using the exposure
compensation setting, up to the full +2.0EV for very open canopies.
•
For more closed canopies, under-expose, up to the full -2.0EV for
mostly closed canopies.
•
If you have sufficient memory, try exposure bracketing to take photos
with higher and lower exposures. Choose the image that gives the
clearest canopy edges.
Note: In the Canon 60D you have to disable the flash for AEB auto
exposure bracketing to work, so the N-S markers will not light up. This
is not such a problem because the North indicator is always at 9 o’clock
in the image.
You can auto-exposure bracket (AEB) and white balance bracket
simultaneously, taking 9 shots.
See pages 100 &122 of the Canon 60D User Manual.
1
This seems wrong at first. Why would you do you want to make a light picture lighter and a
dark picture darker? The reason is that in auto-exposure mode the camera will compensate,
darken a picture of all bright sky, and brighten a picture of an all dark canopy. That is why it
is better to work in fixed, manual exposure mode if you can – but
that
option
depends on the
light being stable – which, of course, is not always so!
