Sky & Telescope - September 2024 - 57

ALAN DYER
Narrowband nebula filters, such as the
Lumicon Ultra-High Contrast (UHC)
and doubly ionized oxygen (O III)
filters deliver an even greater degree of
enhancement.
The UHC and O III filters are subtly
different, however. The UHC spiffs up
faint nebulae without blunting too
many stars. An O III favors the oxygen
emission lines of planetary nebulae but
kills most stars. The Dumbbell makes
an excellent test case for comparing the
effectiveness of each filter type.
Filter Magic
A UHC filter used with my 4.7-inch
refractor doesn't disappoint. The
increased contrast is stunning: at 38×,
M27 is a fat, fuzzy hourglass juxtaposed
against a darkish sky strewn with
stars. Bumping the power up to 56×,
the Dumbbell's middle looks strongly
pinched. Better yet, my averted vision
picks up some extremely pale nebulosity
on either side of the pinch. At 100×, the
central portion is fuller.
An O III filter adds improvements -
and limitations. At 38×, M27's signature
hourglass is superbly contrasted
against a black sky, though the stronger
O III blocks out all the faint stars. At
56×, the hourglass is distinctly enveloped
in an oval bubble of vaporous nebulosity.
Amazing! However, a limitation
hits at approximately 100×: The tenuous
bubble is harder to hold, and the background
is reduced to just the brightest
stars. The overall image is awfully dark
in my little suburban refractor.
The 8-inch reflector equipped with
the O III filter and medium power offers
a well-defined, contrasty nebula. The
twin lobes are subtly textured; the foggy
fill between them blends smoothly into
the Milky Way. But again, higher magnification
erodes the nuanced detail.
The field is dark and lacks starlight.
M27's swollen middle is barely apparent
even with averted vision. Conversely,
the UHC retains decent contrast - plus
a scattering of stars. The hourglassin-a-bubble
effect is evident at 51×
and strengthens with each step up in
magnification. At 135×, the nebula is
impressively large, and its middle porHOURGLASS
IN THE EYEPIECE This simulated, 1°-wide telescopic view of the Dumbbell
Nebula nicely captures the shape of M27 in good sky conditions. The brightest field star is 14
Vulpeculae, and the 11.3-magnitude star mentioned by the author is visible immediately to the
right of the nebula's southwest lobe.
tion is nicely filled out. The object has
morphed into a ghostly planet bulging
at the equator, the textured lobes mimicking
surface features.
I've also studied M27 using a couple
of Tele Vue Bandmate Type 2 Series
narrowband filters. The Bandmate
Nebustar, a refinement of the original
UHC design, provides superior contrast.
M27's wispy equatorial extensions
swell; the hourglass portion
likewise seems brighter. The Bandmate
O III yields better contrast and broader
equatorial extensions than the Lumicon
O III. In addition, both Bandmates
block out fewer stars than the venerable
UHC and O III filters.
More Than a Dumbbell
Ultimately, any narrowband filter will
maximize your appreciation of the
Dumbbell. This classic planetary nebula
truly lives up to its " planetary " label. To
my eye, its overall oval form is similar
in shape to the oblate globe of Saturn,
whose equatorial girth is noticeably
greater than its span from pole to pole.
The misty equatorial extensions of M27
exude a hazy, atmospheric feel, while
the bipolar lobes resemble a pair of massive
continents connected by a slender
isthmus, much like North and South
America. Gorgeous!
As the old saying goes, beauty is in
the eye of the beholder. So, get outside
and behold the Dumbbell-HourglassApple-Earth
Nebula for yourself. You
won't be disappointed.
¢Contributing Editor KEN HEWITTWHITE
has been scoping the Dumbbell
Nebula since the summer of 1968.
sk yand te l escope .o r g * SEPTEMBER 2024 57

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