Sky & Telescope - September 2021 - 65

long a focal length as possible in order
to provide low magnifications. DayStar
recommends Tele Vue Plössl eyepieces
in the 15-mm to 55-mm range. I have
both the 55-mm and the 32-mm models
and used them often with the scope.
The 55-mm produces an excellent view
of the entire solar disk at 48×. Prominences
stand out well, and anytime I
looked at the Sun there were at least
some small ones visible along the limb.
On the Sun's churning disk, spicules are
easily seen, and when sunspots are present
closer to the limb, they really stand
out from the active regions, producing a
three-dimensional appearance.
The field surrounding the Sun isn't
quite black, but rather an unobtrusive,
faint, pinkish glow. Prominences
appeared just as bright and visible no
matter if they were in the center of the
field or placed near the edge.
The best way to describe the view
through a dedicated Hα solar telescope
is " electric. " Solar Hα light is a bright
reddish pink - like a neon sign on
steroids. Photographs really don't capture
the vibrant appearance accurately.
Slightly out of focus the Sun is a pinkish
blur, but as I turn the focuser, the
details simply pop into focus, and I feel
a mental jolt at the intricate scene.
A 32-mm eyepiece produces 83× and
brings out even more surface detail.
The Quantum
Control
software graphically
displays
the status of
the telescope's
internal filter and
allows users to
adjust the filter's
bandpass.
One particularly active region surrounding
a small cluster of sunspots
was a real treat to observe. Prominences
are also more pronounced, as the higher
magnification also increases contrast.
I also tried some eyepieces in the scope
with focal lengths in the range of 20
mm or less, but the daytime atmospheric
seeing just would not cooperate.
DayStar also warns that anything
shorter than 12 mm produces magnifications
beyond the diffraction limit of
the instrument.
In practice, warm, turbulent daytime
air limits how much you can push
magnification anyway. On a morning
of good seeing, a 24-mm Takahashi
LE eyepiece provided great views, but
I could not go beyond that. The Moon
is nearly the same apparent size as the
Sun, and at night you can often get
great high-resolution views of it that
approach the resolution limits of your
telescope. Daytime skies, however, are
far less forgiving.
Imaging Performance
Naturally, with the addition of a few
adapters, you can also use the SR-127
for solar imaging. As Hα light is a narrow
wavelength found in the red end of
the spectrum, a color camera is unnecessary.
Those amazing color images of
the Sun you often see were shot with
monochrome cameras and colorized
after the fact.
The telescope includes sufficient back
Daystar offers an optional FlatCap diffuser
that permits imagers to use the Sun as a light
source for making flat-field calibration images to
correct for uneven illumination and dust motes.
focus to accommodate a 90°-star diagonal
and a wide range of eyepieces. However,
you'll need an additional extension
tube to get to focus when imaging
straight through without a diagonal.
I find it much easier to have a motorized
focuser when imaging so I can do
everything from the computer. I added
sk yand tele scope .o r g * SEPTEMBER 2021 65
a small Optec focuser on the back of
the existing focuser, and even with this
added weight the focuser never slipped.
The added focuser took up enough back
focus that additional spacers weren't
necessary.
Once focus is achieved, imaging is a
snap - I just had to remember to keep
my videos to about 30 seconds in length
Another helpful accessory for Hα solar imaging
is DayStar's optional Interference Eliminator.
This device allows users to slightly tip their
camera in order to remove interference patterns
known as Newton's rings (bottom image).
These rings arise from reflections between the
cover slip of a digital detector and the rear element
of the etalon filter.
https://skyandtelescope.org/
Sky & Telescope - September 2021

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