Filter Configurations
Since the introduction of the
modified Canon 300D's, we have
continued field testing and experimentation and
arrived at a two-filter system as an optimal
configuration to satisfy both astronomical
and conventional photo needs. This consists of:
- Replacement of the original
(rear-mounted) Canon IR blocking filter
with either a clear or Type I UV/IR
blocking (H-alpha pass) filter as
currently offered.
- Optional supplemental (front-mounted)
filter which is user-accessible.
The reasoning behind creating two filter positions is
that some narrowband filters generate
reflection artifacts when placed close to the
imaging sensor, and the front-mounted optional
filter provides more flexibility of filter
selection to the user.
The rear-mounted filter is permanently
installed by Hutech at the time of order and
may be one of two types:
- Clear filter - This passes
all bands (including IR) and includes a
fully multi-coated anti-reflection (AR)
coating effective between 380 and 1000
nm. This allows the user to fully
utilize the sensor's sensitivity into the
IR band, but requires an IR filter to be
inserted at the front-mounted position
for most "normal" use. The clear filter
is compatible with the Canon auto-focus
function.
- Type I filter - This UV/IR
blocking filter allows H-alpha to be
recorded, and is the most cost-effective
way to adapt the Canon digital cameras
for astronomical use but does not allow
IR photography to be done.
This filter
is compatible with the Canon auto-focus
function. An additional filter in the
front-mounted position or the camera's
custom white-balance function may be used
to achieve proper color balance for
non-astronomical photography.
The front-mounted filter holder is installed between
the camera's lens bayonet and the viewing
mirror and is designed for easy filter
switching by the user. Front-mounted filters
do not affect the camera's auto-focus
operation but preclude the use of Canon EF-S
lenses or some lenses designed for APS-C sized
sensors and affect the closest
focusing distance for each lens.
These filters will be available for the
front-mounted position:
- Light Pollution Suppression (LPS) filter
- Type I filter, standard UV/IR blocker
for use when a clear filter is installed in
the rear-mount position.
- Type II filter, UV/IR blocker more suitable
for daylight photos. Allows the Canon 20D to
shoot daylight photos in AWB mode as
detailed below.
- Infrared filter (must be used with a
clear filter in the rear-mount position).
- H-alpha filter (FWHM: 8nm)
- Nebula filter
Daylight Photography with Type II Filter
With the new Type II astronomical IR blocking /
H-alpha pass filter, daylight photography color
balance is greatly improved. However, after
further field testing, we find that the IDAS
Type II filter does not perfectly correct color
balance when used with Canon's Auto White
Balance (AWB) function. To assure that color
correction is accurate, Hutech will supply (at
no additional cost) PC software which will
correct the files shot in AWB mode on the
memory card in a batch operation. This software
may be used with both the 300D and 20D, and
will be available for download on the Hutech
web site shortly.
The Canon 20D also includes an internal
capability to correct AWB mode color balance
when the Type II filter is used. Optimal
settings for the 20D are currently being
determined.
The Canon camera price list will be updated
shortly.
If you have any questions please
contact Ted Ishikawa
(ishikawa@hutech.com)
at Hutech.
