Sky & Telescope - September 2021 - 64

S&T Test Report
tAn LCD digital readout displays the exact
bandwidth of the internal Quantum solar filter.
An LED status indicator at right appears yellow
as the filter is stabilizing and changes to green
when it has reached its target temperature. The
red button increases the filter passband, and
the blue button decreases it in order to display
wing-shifted features in the chromosphere.
The SR-127 incorporates additional
optics to achieve its long 2,667-mm
(f/21) focal length in such a comparatively
short 74-cm (29-inch) optical tube
and ensure the light rays are as parallel
as possible before entering its etalon
filter. An inline blocking filter reflects
nearly all of the unneeded incoming
sunlight out the front of the refractor,
letting only a small portion of that concentrated
energy reach the main etalon.
Basic Operation
The scope's temperature-regulated
etalon filter requires electrically generated
heat to precisely control the width
of the passband. DayStar includes an
AC adapter, though you can also use
a 12-volt supply provided it produces
at least 1.2 amps. An LCD screen on
the side of the tube near the focuser
displays the current passband. A status
LED appears yellow while heating or
cooling to the proper temperature,
then turns green when it's ready for
use. The filter heats to between 100°
and 150°F (38° to 66°C) and takes
about 10 to 15 minutes to reach temperature
after initial power-up. Adjustments
to the passband may take as
much as 5 to 10 minutes for the filter's
temperature to settle, though in my
hot Florida climate it often took only
a minute or two. The red and blue buttons
to the right of the display adjust
the passband in increments of 0.1 Å
from the central value of 6562.8 Å.
The reason there's a range of adjustments,
rather than a single " set-andforget "
setting is to compensate for
what's known as wing shift. Features
in the chromosphere, particularly
prominences, can evolve over short
time spans, sometimes changing within
a few minutes. This is due to plasma
travelling along magnetic fields at
speeds fast enough that they can actually
be blueshifted when approaching
the viewer, and redshifted as they race
in the opposite direction. The effects
are noticable along the limb of the Sun.
You can use the red and blue buttons to
slightly adjust the passband by as much
as +/- .5 angstroms to bring out these
wing-shifted features. However, it may
take some practice to be able to see the
difference. When studying features
along the solar limb, you can see these
changes in brightness and contrast
more easily at high magnifications.
Some features required a change of .3 to
.4 angstroms to see an improvement in
contrast and clarity.
The Sun is a relatively large target,
so at the scope's focal length of 2,667
mm, you should use an eyepiece with as
Under good seeing, the SR-127 produces high-resolution images of sunspots, filaments, plages, and even prominences. This excellent photo of
AR 2786 was recorded in late October 2020 using a ZWO ASI120MM monochrome video camera. The image at right is the same picture colorized for
aesthetic purposes. The Sun appears bright reddish pink through this and any hydrogen-alpha solar filter.
64 SEPTEMBER 2021 * SKY & TELESCOPE

Sky & Telescope - September 2021

Table of Contents for the Digital Edition of Sky & Telescope - September 2021