On spectrum enhanced cameras with astronomical filters replacing the standard
Canon IR-blocking filter, daylight shots will show an overall
red cast due to
the increased red wavelength sensitivity. To correct this several
methods may be used:
- Color correction filter (front-filter or on lens)
- Custom White Balance camera function
- White Balance Correction camera function
Color correction filter
For cameras accommodating front filters, the VLC daylight correction
filter is available as a Hutech option. This allows the camera's
standard white balance and metering functions to operate normally.
For cameras unable to use front filters, lens-mounted VLC filters
are also available in 58mm, 67mm, and 77mm sizes. The advantage of
using these filters is that color correction applies to all
photos taken, including those taken in full auto mode.
Custom White Balance camera function
The Custom White Balance function can also be used to electronically
compensate for the excess red of an enhanced camera. To use this method,
a white target such as a piece of paper should be photographed as follows:
- Set the target under the appropriate lighting (e.g. sunlight).
- Set the camera's white balance setting to match the lighting.
- Position the camera so the target fills the field of view
- Set the camera for manual focusing (focus is not critical).
- Take a photo using the camera's auto-exposure setting
After the photo has been taken, set the camera for "Custom White Balance"
and select the photo of the white target as the reference. Refer to
your camera's manual for details specific to your camera model. Note that
when shooting under different lighting conditions you must create a separate
white balance reference image for each setting and be sure to select the
appropriate reference image.
White Balance Correction camera function
For recent model cameras, such as the 40D, with the correction
function and Type Ib filters, the camera can be manually
adjusted to compensate for the red bias without using a white target.
To use white balance correction, select "WB Shift" in the camera's menu and use the
camera's pointer control to move the cursor towards the B / G
quadrant of the color matrix. Using this method of color
correction has the advantage of still allowing the use of
the camera's color balance function (based on
your selection of the light source) or operation in fully
automatic operation (Program Auto) mode.
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