Possibly the best kept secret in nebula filters, the GCE filters from DGM Optics
I
live in a heavily light-polluted area, right in one of the five
boroughs of New York City. It's unfortunate; But, like other (dedicated)
urban observers, I don't let it stop me from enjoying visual astronomy.
For me, it's DSO's; In fact, it's almost always been DSO's for me.
Except of course, for that first year... With the first small refractor
kit - Back when I was 14 years old: During my first year of observing, I
went for planets and the moon. Well, I'm 48 now - And I'm a confirmed
chaser of faint fuzzies. It also seems that I appreciate and enjoy
binocular astronomy more and more each year. I'm always on the lookout
for that next instrument (usually Binos these days), or an accessory to
help me fight light pollution. Generally, anything that will give me a
bit of an advantage help me to locate and view fainter and fainter
DSO's.
For a few brief years (while in my late 20's) I
was fortunate enough to own and use some fine optical instruments: A
TeleVue Pronto (70mm refractor), along with Televue and Takahashi EP's;
Fujinon 7x50's & 16x70's - Both with proprietary screw-on
Fujinon nebula filters, as well as an 8" Dobsonian with lots of nebula
filters... I took a short "hiatus" from astronomy for a while (while
pursuing other hobbies), and ended up selling all of my high-quality
equipment.
Today, my equipment consists of the
following: Bushnell 8x30's, Barska 15x70's, Garrett Signature Series
10x50's, Celestron 80mm Spotting scope (20-60x), Bushnell 5" Truss Tube
Dob, Apertura AD8 8" Tweaker's Dream Dob, Standard Bushnell &
Apertura EP's, Tripods, and lots of Nebula filters...
My latest
accessory purchase, was a pair of unique "nebula" filters from a company
called DGM Optics. Not only are these filters priced lower than many
other companies' offerings - But, according to an excellent review I
read, they perform better than filters from the other well-known
companies!
I ordered a pair of their GCE filters for use on a couple of pairs of binoculars, etc., to help me in spotting DSO's.
GCE stands for Galaxy Contrast Enhancement! Neat, huh? Of course, I was initially very intrigued by them.
Well,
it's true - I've seen it for myself now; using a pair of them on my
Garrett Signature Series 10x50 binoculars (and also on EP's, with my 8"
Dobsonian).
I have no affiliation with DGM Optics, by the way (aside from being a satisfied customer).
Here are the filters screwed onto the threaded eyepiece barrels of my 10x50's - This is basically their permanent location now.
As
far as I know - These are the only filters currently in production,
that are actually indicated for the image enhancement of galaxies! I
think this is great! And although (as one would expect) the difference
isn't jaw-dropping - So far, I have seen a noticeable improvement when
viewing several of the brighter galaxies: M31, M51, M101. And I'm really
looking forward to using them on many more (smaller & fainter)
galaxies!
These filters are great for use on small aperture
instruments - especially Binoculars. One of the reasons for this, is
that they allow a generous amount of light through (while blocking light
pollution, of course).
At a quick glance, they could
be considered close to a 'Broadband' type of light pollution filter - As
opposed to say, a UHC-type for example. I suppose the only popular
filters that they could be compared to, would be the 'Deep Sky' types.
However the GCE's actually do improve the view on galaxies in my heavily
light polluted backyard.
I've never taken the time to accurately
determine what the NELM is at my observing site. But, I would say it's
about magnitude 4 (maybe 4.5, on a really good night!). Using the GCE
filters on my Garrett 10x50's, mounted on a good Manfrotto tripod set,
I've been able to see (and confirm) the following objects: The Rosette
nebula, The Christmas Tree Cluster, The Eskimo Nebula (NGC 2392), IC 405
& 410, and Pk219+31.1. There are a few more faint nebula that I
thought I may have seen, using averted vision - But, cannot confirm
100%, so I haven't listed them.
This was just during the first few weeks since their arrival.
The
GCE's give all objects under observation an interesting hue of magenta.
Sort of a pinkish/purple, that I happen to find pleasing. It doesn't
seem to be as restrictive, or distracting as other nebula filters that
I've used. Anyone who has an assortment of nebula filters in their
collection knows what I'm referring to.
In addition to
my 10x50's, they perform very well when carefully taped to the
eyepieces of my cheap Barska 15x70's. I also use one with my 8"
Dobsonian when scanning/searching for DSO's, using wide-field (30
& 25mm) 1.25" eyepieces. They work very well on my higher-power
EP's also (10 & 9mm).
I was going over my
Astronomy notes recently...And realized, that there are some interesting
technical details about these nebula filters that I can share. This is
info copied directly from DGM Optics, hence the quotations: My comments
are italicized.
"The Galaxy Contrast Enhancement™
filter aids in the visual observation of galaxies and milky way dust
clouds and dark lanes. The GCE filter takes a different approach to
enhancing galaxy observation by allowing high transmission through
nearly the entire visible spectrum while rejecting only the harmful
light pollution wavelengths. Because of those attributes it also is a
very good general purpose LPR filter, unlike traditional wideband
filters, which exclude most of the red portion of the visible spectrum. -
I like this very much, because until now, it seemed that you couldn't
"have your cake & eat it too" - If you used a broadband filter,
from other manufacturers, some of the desired wavelengths were getting
blocked as well (especially the desired red).
"Specifications
The
GCE filter design stresses maximum optical throughput utilizing
state-of-the-art optical thin-film designs and materials. This filter is
a “first surface” hard oxide thin-film and is much more durable and
long lived than laminated “soft film” designs used by several famous
makers." - I'm also very happy about this, no one wants a light
pollution filter with a surface that will deteriorate over time.
"They
are also much less prone to the internal reflectance problems that
plague laminated filters. Laminated filters can produce a very
undesirable “doubling” of stellar images often with one of the doubles
being red. Contrary to popular belief, this image doubling is not due to
the red sideband component that many nebula filter designs produce, but
in many cases is due to laminated glass not being exactly parallel to
the protective cover plate after lamination. Many laminated filters
display this annoying characteristic." - After learning about this, why
would anyone want to buy an inferior nebula filter again? I won't be!
"This
filter averages around 1% Transmission (optical density of 2) through
the rejection region from 540 to 590nm, and average transmission greater
than 90% Transmission in the passbands, and greater than 75% at the
656.3nm H-Alpha line. The design yields a filter with a very symmetrical
shape and high optical throughput, for maximum enhancement of nebula
with a minimum of loss of stars in the field of view.
The
substrate is quartz and has measured total wavefront values of .25
waves. - I find this fact awesome. These filters don't use plain glass
as their substrate; it's Quartz!
The combination of first surface
optical thin-film technology and a polished, flat substrate enables
this filter to be used with high magnification, a real plus for small
planetary nebula." - And, finally, this last part - about being "a real
plus for small planetary nebula" It just so happens, that I have become
very interested in hunting planetary nebula recently So, I was also
happy to read this.
If there is any area that has room for
improvement, it would be with the (1.25") metal filter housing. The
small notches on the outer diameter of the filter housing: These serve
to provide a better grip, or traction for a user's fingertips (while
screwing the filters on or off of EP's). It would be nice, if they could
be made to be less likely to slip between fingertips. My other nebula
filters seem to be easier to hold on to, by allowing fingertips to gain a
firmer grip. The actual filter cells on these GCE's could be considered
"low-profile" when compared to the Zhumell brand filters, for instance.
As for me: One of the joys of using this
GCE filter - Is that I simply leave a pair of them screwed into the
threaded EP barrels of my Garrett signature series 10x50's - And, I just
leave them attached all the time. I don't find my views of Asterisms,
or Open Clusters darkened very much at all. Yet, they improve the views
of all DSO's at same time. They constantly help me to detect nebulas (of
all kinds), which I simply could not/would not see without the filters
in place. I've actually tested this quite a few times.
It
would be great, if someone who has other name-brand "Broadband" LPR
filters (or DeepSky/SkyGlow types) could also do some tests verses the
GCE filter...
The smallest (good-quality) binoculars I currently
have, are my Garrett 10x50's. But, I believe these filters would also
perform well on smaller Binos (if one were willing to experiment) -
Which would be great when scanning for/observing even larger, diffuse
DSO's. In fact, I believe I just gave myself an idea for a future
project...
In conclusion, I just wanted to share my experiences. I
happen to be a huge fan of binocular Astronomy (and nebula filters!).
And, hope that fellow Astronomers, who have similar interests, will find
these GCE's to be a useful addition to their equipment.
Clear skies!
