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A standard Canon
350D has a filter over the sensor which absorbs infra red light. Unfortunately
for astronomers, the filter removes a substantial amount of the red light that
is given out by emission nebulae. It is possible to get the filter removed, and
replaced by one with a less drastic cut-off. This
webpage
shows why it is best to get an expert to do it!
This change will make the camera
unusable for ordinary purposes. For this reason, I
bought another 350D on Ebay and sent it off to
Astronomiser to have a filter
change. In less than 48 hours the camera was back, and the two pictures below
show the difference between the two filters.
Hopefully the skies will clear soon
and I can try it out properly. |
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Canon filter |
Baader filter |
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This
spectrum picture (from astrosurf.org)
shows how much more is gained by removing the filter. If the filter is not replaced by a Baader filter even more deep
red light can get to the sensor, but the difference is unlikely to be visible
in light polluted regions. The Baader filter also keeps dust from landing on
the sensor. |
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The
important wavelength for astronomy is the Hydrogen Alpha line 6563 which is
almost completely removed by the Canon filter. |
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Unfortunately light pollution is mostly Sodium 5893 which is also
going to be boosted. It may be necessary to use a CLS pollution
filter... |
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