Sky & Telescope - June 2024 - 57

before you pack up your camera for
modification. First, the autofocus may
no longer work. Some cameras may have
an internal adjustment that may restore
this capability, however. Another catch
is that unlike a multi-billion-dollar
company with vast resources to spare
for clean-room environments, when you
send your camera to a smaller, specialty
firm (or individual) for modification,
it may acquire some dust between the
sensor and the new filter. The effects are
usually very slight, but the pixel peepers
among you will notice. When this
occurs, you'll need to resort to flat-field
techniques or some post-processing,
cosmetic corrections. (As always, it's
best practice to shoot in RAW format
for easier post-corrections.) Finally,
when shooting with a modified camera
your daytime images will have a strong
reddish or pink tint to them. You can
easily correct this with a custom whitebalance
setting, either in camera or
applied during post processing.
The fact that the natural colors can
be restored for daytime photography
is important because it means your
camera will be able to do double-duty
- astrophotography and whatever else
you want to shoot during the day.
There are also numerous clip-in filters
available that restore your camera's
original UV/IR performance. These let
you do daytime photography without
the need for post-processing heroics to
fix the color balance.
Soaking Up the Full
Spectrum
So far, I've been describing modifications
that are something of a compromise
- procedures that enhance
nighttime performance while retaining
daytime capabilities. But you can go allin
if you want with a " full-spectrum "
modification. This means replacing the
camera's original filter with clear glass
so that all wavelengths of light reach
the sensor. However, you'll be sacrificing
autofocus capabilities for sure,
which you're not likely to miss at night
anyway. With a full-spectrum modification,
you have the option of adding
clip-in filters that emphasize specific
NORTHERN CYGNUS The constellation Cygnus, the Swan, is rich in hydrogen-alpha
emission nebulae. You can easily see the North America, Pelican, and Gamma Cygni
nebulae in this image captured with a Canon EOS Ra camera and a 200-mm lens riding
on a star-tracker mount.
parts of the spectrum. For example, you
can get a filter that passes only UV or
IR light. You can even get a filter that
restores the normal UV/IR balance! A
great source for many types of clip-in
filters is astronomik.com.
I took this route myself with a
Canon EOS Rebel T3i and use a clipin
IR filter to turn the camera into an
infrared DSLR. Looking through the
viewfinder I can't see anything at all, so
I have to use the LCD screen to frame
my shots. Daytime IR photography is a
fantastic artistic pursuit in itself, and
different IR filters can be used to create
altered-color images that are simply
otherworldly. You can also shoot the
Moon with an IR filter - a strategy that
helps mitigate the blurring effects of
atmospheric seeing. IR also lets your
camera peer through dusty regions to
better show stars and structures not
apparent in normal, visible light.
I've saved the very best option for
last. Both Canon and Nikon have produced
cameras with modified internal
filters specifically designed for astrophotography.
Canon was first out of
the gate when it released the EOS 20Da
in 2005 (the lowercase " a " denotes
" astro, " of course). It followed up with
the EOS 60Da in 2012 and finally the
EOS Ra in 2019. Nikon also got in the
act and released the D810A in 2015.
I've used all of these cameras except the
D20Da. With the exception of the EOS
Ra and D810A, the rest required manually
setting a custom white balance to
correct an excessive red cast in daylight
photographs.
Unfortunately, these cameras are no
longer in production. The good news
is they're not difficult to find used and
in excellent condition. Fingers crossed,
Canon or Nikon will release new astro
cameras in the near future.
Thankfully, there are several places
to purchase a suitably modified camera
and services that will perform the filter
surgery for you. And if you're good with
tools, you can even try it yourself. If you
want to extend your astrophotographic
reach, there are plenty of options.
¢Contributing Editor RICHARD S.
WRIGHT, JR. loves traveling to dark skies
to turn his Canon EOS Ra loose on the
Milky Way and bright emission nebulae.
sk yand tele scope .o r g * JUNE 2024 57
http://www.astronomik.com http://skyandtelescope.org
Sky & Telescope - June 2024

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