Sky & Telescope - April 2020 - 65

haze over the image. But filtering out IR
also filters out most of the deep red Hα
emission at a wavelength of 656.3 nm.
Not so with the EOS Ra. Its factoryinstalled IR-cutoff filter transmits a
much higher level of Hα than the stock
EOS R.
I found that the Ra's ability to record
red emission nebulosity to be on par
with my modified Canon EOS 5D Mark
II that I've used for almost all my deepsky imaging since 2009. My venerable
EOS 5D MkII is an example of a DSLR
that was modified by a third party, in
this case Astro Hutech (hutech.com).
It appears that Canon has given the
new Ra camera a filter with greater
transmission of Hα emission than on
its earlier "a" cameras. The Hα performance of the Ra proved better than
Canon's previous 60Da. Whether it will
match the performance of "spectrumenhanced" cameras modified by third
party vendors will depend on the filters
those cameras use. Some, dubbed "full
spectrum" cameras, use no IR-blocking
filter at all.
The EOS Ra is certainly not a fullspectrum camera, but then again it
doesn't require the addition of costly
clip-in filters to cut infrared for normal
daytime use.

Daytime Use
The advantage of purchasing Canon's
enhanced-red Ra camera is that the
manufacturer has calibrated the camera's white balance to produce a nearly
normal color rendition even when
using Auto or Daylight White Balance.
Custom White Balance, a necessity
when using third-party modified cameras by day, isn't required with the Ra.
Where the Ra's added red sensitivity did
become apparent in "normal" use was
during twilight and sunset shots, which
recorded with rich reds.
While it can be used by day "as is,"
the EOS Ra is definitely not for subjects
in which color accuracy is critical. I
wouldn't shoot weddings or portraits
with it!

u Due to its factory calibration,
shooting the EOS
Ra by day (left) at
a daylight color
temperature of
5200 K produces
a raw file (as of
firmware version
1.6) that looks
similar to that of
a normal camera,
a Canon 6D MkII
at right, also shot
at 5200 K. The
EOS Ra can be
used for normal
photography.

Canon EOS Ra
at 5200 K

screen sensitive enough to allow framing
dark nightscapes, and to show enough
stars through a telescope to identify your
field, perhaps even your target, all on its
comfortably tilted rear LCD screen. That
improvement alone makes the upgrade
to an EOS mirrorless camera very attractive for astrophotography.
The EOS Ra has one welcome firmware upgrade over the standard EOS R
that benefits astrophotography. Instead
of Canon's standard 10× magnification
in its Live View focusing feature, the
EOS Ra offers 30×, great for precisely

Canon 6D MkII
at 5200 K

focusing on stars. I found this especially
useful when focusing wide-angle lenses
with their tiny star images.

Image and Edge Artifacts
The long exposures and extreme contrast-stretching applied when processing deep-sky images can reveal image
flaws that go unnoticed in conventional
photography. However, I found no
issues with "star eating," nor discolored
stars that plague some manufacturers'
cameras. There were no edge-glows or
light-leaks and, as expected for a mir-

q The EOS Ra (far left) picked up the North America Nebula with richer red nebulosity than Canon's 60Da camera (far right), and with a level similar to the author's third-party modified EOS 5D
MkII. By comparison, images with the stock EOS R and 6D MkII show what a normal camera typically records - very little red nebulosity. This comparison set uses single raw images processed
identically to increase contrast and neutralize the sky background, but without any alteration of the
nebula colors.
Canon
EOS Ra

Canon
EOS R

Canon
6D MkII

Canon
5D MkII
(modified)

Canon
60Da

Framing and Focusing
Both EOS R cameras offer a Live View
sk yandtelescope.org * APRIL 2 02 0

65


http://www.hutech.com http://www.skyandtelescope.org

Sky & Telescope - April 2020

Table of Contents for the Digital Edition of Sky & Telescope - April 2020

Contents
Sky & Telescope - April 2020 - Cover1
Sky & Telescope - April 2020 - Cover2
Sky & Telescope - April 2020 - 1
Sky & Telescope - April 2020 - Contents
Sky & Telescope - April 2020 - 3
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