As of 8/20/06 DGM Optics began a partnership with Omega Optical of
Brattleboro VT. This partnership involves my LPR/Nebula filters which
will be manufactored, and sold through Omega Optical. In addition to
the NPB (Narrow Pass Band) and VHT (Very High Throughput) nebula
filters we have 2 new filters which will be available within the next
1-2 weeks. First is an OIII and the second, and most interesting, is
the GCE (Galaxy Contrast Enhancement).

The GCE filter takes a unique approach to galaxy observation by using a
"rejection band" design. A rejection band design essentially allows all
of the visible spectrum to transmit while blocking only undesirable
wavelengths. The resulting filter has the most total throughput of any
LPR filter I`m aware of, and as such, has a very neutral impact on star
brightness and color.

This spring we did a small prototype run as a kind of "what if" for the
design and sent some out for folks to test. The prototype is not an
optimized high transmission filter (it averages about 85% TX) but even
still has yielded some encouraging results. The production version of
these filters will feature average TX of around 95%.

The first of the GCE filters should be available within 1-2 weeks and
as of this post we have small inventory of OIII`s.

Here are some initial reports and impressions for the prototypes;

Galaxies: Performance seems to be different relative to Population I
vs. Population II stars (core vs. arms; bluish vs. yellowish). Better
for the yellowish (Population II) galaxies. M31 is very nice with this
filter and the obscuring dust lanes are somewhat more pronounced. M33
is also improved. However because galaxies spectral profiles are
generally broadband in compostion do not expect them to jump out the
way nebula do with the NPB and VHT filters.

Deep Sky: The GCE seems to be a very good deep sky filter and generally
does a nice job with same objects that are improved with the NPB and
VHT filters. Because the GCE`s spectral characteristics are broadband
they don`t enhance as strongly as NPB or VHT filters but because they
feature such high overall optical throughput and specific rejection you
can observe with them and don`t have to cup your eye to keep out stray
light. Recently I have found the GCE does an excellent job with milky
way gas clouds and obscuring dust lane, lending the numerous light and
dark region an almost 3D quality. The North American nebula and the
surrounding area is quite pleasing with the GCE.

Deep Sky CCD: The jury is still out on this one, but I was told by
several folks who have seen the spectral scans of the GCE that it may
be a good filter for deep sky CCD work. One of the prototypes is hands
of at least one experienced astro-imager.

However the GCE will not allow you to detect galaxies which are not
already detectable under given conditions, and as always when
considering filters, they are not a substitute for aperture and dark

clear skies!
Dan McShane
DGM Optics