Canon Camera Hackers Manual page 41

32
C H A P T E R 4 Teach Your Camera New Tricks
minimum shutter speed depending on the focal length and the factors
specified in the following entries. The numeric settings (1/8, ..., 1/1000)
specify a fixed minimum shutter speed. The camera will try to use this
or a shorter speed. Typical values would be:
1/8 – 1/30 for slow movement
1/60 – 1/125 for general movement (kids, pets, etc.)
1/125 – 1/1000 for fast movement (sports, etc.)
User Factor (1/FL Factor). An old rule says that you should use the value
f
of 1/focal_length as your shutter speed to avoid camera shake. How-
ever, this rule was made for 35mm cameras. To adapt this rule to the
optics of a digital camera, you need to specify the lens factor. To find out
that factor, first switch the display of the focal length to EFL (35mm
equivalent). This is done in OSD
(section 4.2.7). Now read the focal length (Z) from the display. Then
switch the same entry back to FL (true focal length). Again read the focal
length (Z) from the display. Divide the first value by the second. This is
the start value for the User Factor. For example: on my SD1100 with its
1/2.5 inch sensor, I get an EFL of 38 mm and an FL of 6.2 mm in wide-
angle setting. The resulting focal length factor is close to 6.1. Cameras
with a 1/1.7 inch sensor have a focal length factor of 4.6.
Now you can modify this value according to your ability to hold the
camera steady. If you think that you can hold the camera quite steady,
or if you are able to lean your body against some solid object, subtract
20 percent. If you are quite shaky, add 20 percent. When the camera is
mounted on a tripod, dial-in the smallest value possible (1).
When shooting in a vibrating environment such as an airplane, the
User Factor (which is limited to an upper bound of 8) may not be suit-
able. Depending on the strength of vibrations, the above shutter speed
formula must be modified to approximately 8/focal_length. Then the
User Factor must also be multiplied by 8—too large to dial in. So in-
stead, compute the minimal shutter speed from the EFL-reading (35mm
equivalent) with the help of this formula and set it as a fixed value in
Minimal Shutter Speed.
IS Factor (Tv* Factor). This factor takes the Image Stabilizer into account.
f
An average Image Stabilizer will give you an exposure time extension of
an approximate factor of 4 (2 f-stops) without risking shake, a poor
Image Stabilizer about a factor of 2 (1 f-stop), and an excellent Image
Stabilizer a factor of 8 (3 f-stops). Newer camera models usually have
more powerful image stabilizers than older models. You can look into
test reports (for example, on www.dpreview.com) to find out about the
effectiveness of your camera's IS system. Or do some of your own mea-
surements. Hint: Switch the Image Stabilizer off in environments with
strong vibrations. It's built to correct hand shake, not vibrations with
higher frequencies.
> Miscellaneous Values > Zoom Value