Canon Camera, Руководство хакера

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C H A P T E R 4 Teach Your Camera New Tricks
better suited for scientific work. Of course, the real limits
2
of this range are
defined by the camera hardware, but see sections 4.3.6 and 4.3.5 for very
long and very short exposure times!
The same applies for ISO and aperture settings. For example, dialing in
an ISO value of 6400 will have no effect if your camera only supports ISO
1600: the sensor speed, will be set to 1600. Remember, too, that in the case
of the ISO speed, the
Override value is the “real” ISO value—not the
“market” value, which is approximately 1.6 times higher. So if you dial in an
ISO value of 1000, the
Review Mode will show an ISO of 1600.
For most cameras, the CHDK allows higher ISO values than what the
native camera menu has to offer. On my SD1100, for example, the ISO scale
ends at ISO 1600. The CHDK, in contrast, allows me to shoot images with
ISO 6400 (dialed in as ISO 4000). Of course, you may rightfully ask, what
about the noise? Aren’t images shot at such high sensor speeds extremely
noisy? In most cases, this is true, and it’s probably the reason why manufac-
turers put an artificial upper limit on the ISO value. But there are situations
where such ISO values can be useful. One example is when you use the
averaging technique for hand-held night shots (section 4.5.6). In such a
situation, a sharp and noisy image is more useful than an unsharp image
with less noise. The noise can be remedied by averaging a dozen shots or so.
Even in the case of single shots, there are options. PC-based noise re-
duction programs such as NoiseNinja or NeatImage can do a better job
than the camera does, and there are also some RAW converters with re-
spectable noise suppression capabilities.
Two more entries need an explanation:
f
Clear override values @start . If this option is enabled, all values are reset
to their default when the camera is powered up. Otherwise, the Over-
rides remain in place even after the camera is switched off.
f
The option Enable Fast Ev switch turns the UP and DOWN buttons into
exposure correction buttons. This makes sense because you don’t have
to step through the Canon menus to set an exposure correction value.
2 For the real limits of your camera, please see http://chdk.wikia.com/wiki/
CameraFeatures .
Figure 4-18
Japanese teapot detail. Photographed
with a Canon Digital Elph SD1100 as a
DNG file. An ISO of 4000 was dialed in,
the camera’s reading was 6400, and
the EXIF data recorded 6121. Exposure
time was 1/20 sec (per Override), the
aperture f/2.8 at a focal length of
6.2 mm (~ 38 mm). The red color of the
teapot and the nearly monochromous
character of the image kept the noise
low because noise is dominant in the
blue channel. Developed with
CaptureOne Pro 5.0, which features
excellent noise reduction.