Lessons Learned

Filter Comparisons For Common Nebulae

Submitted by David W. Knisely - Dec 19th, 2005
Learned: Personal


by David Knisely
Prairie Astronomy Club

The following is a summary report of visual observations of emission
nebulae comparing the performance of various filters intended for such

The instrument used is a 10" f/5.6 Newtonian, working at 52x, 59x,
70x, and 141x, an 80mm f/5 refractor (15x) and a few unaided-eye observations using the filters hand-held and looking up at the sky (for Rosette, North America, California, and Barnard's Loop).

The filters used were Lumicon's DEEP-SKY, UHC, OIII, and H-BETA, and were usually all mounted in a modified Lumicon Multi-filter Selector.

This allowed rapid comparisons between filters,thus avoiding some of the judgement problems caused by the time needed to change filters or reports from inaccurate single-observation anecdotal accounts.

Observing was done from a dark-sky site (visual naked-eye limit 6.5
to 7.0). For detailed descriptions of the objects, see any of the various
observing handbooks.

Two methods were used for rating filter performance.

In the first method, each filter was given a 0-5 point "Score" performance ranking behind it for each object observed;

Example: OIII (4) means the OIII gave a large improvement in the view over non-filter use and contributes 4 points to its overall score total.

Items such as overall surface brightness, area of nebulosity observed, and contrast of detail were used to judge how well a filter improved the view.

However, since this judgement contains some of the personal preferences of the observer, the exact results may be somewhat subjective in the long run.

Different observers might have slightly differentratings of various filters on various objects, so small differences in judgments are to be expected.

Still, the scoring does on average give a reasonable idea of overall filter performance.

"Scoring" Legend
(5): Very Large Improvement over no filter.

(4): Large Improvement over no filter.

(3): Moderate Improvement over no filter.

(2): Slight Improvement over no filter.

(1): No improvement or slightly fainter than no filter.

(0): Much worse than no filter (object marginal or not visible).


(90 objects as of November 7th, 2002)

UHC...... 316 points, average rating 3.51

OIII..... 290 points, average rating 3.22

DEEP-SKY. 197 points, average rating 2.19

H-BETA... 127 points, average rating 1.41

The second method is a somewhat subjective recommendation for the best
filter to use on the given object, based mainly on a personal judgement, and thus is more a matter of opinion and taste.

The nebular brightness, total
area shown, contrast of details, and overall view are all weighted to give an opinion of which filter will work well for which object.

Other observers would doubtless have somewhat differing views on recommendations for the
specific objects which were observed.

When objects were best seen in two
filters (ie: nearly equal or beneficial performance), both filters would be given the recommendation for the object, with the one yielding the better overall view being listed first and the "close second" best listed next to it.


UHC best on 36 nebulae, close second best on 46 nebulae.
TOTAL 1st and 2nd RECOMMENDATIONS for UHC: 82 objects.

OIII best on 36 nebulae (biased by the inclusion of some planetary nebulae),
close second best on 21 nebulae. *NOT* recommended on 6 nebulae.
TOTAL 1st and 2nd RECOMMENDATIONS for (OIII): 57 objects.

H-BETA best on 13 nebulae, second best on 2 nebulae.
*NOT* recommended on 39 nebulae!
TOTAL 1st and 2nd RECOMMENDATIONS for H-Beta: 15 objects.

DEEP-SKY best on 7 nebulae, second best on 2 nebulae.
**Provided at least some slight improvement for all nebulae surveyed.
DEEP-SKY: 9 objects.


So far (with a few notable exceptions), the numbers show the UHC and OIII are the filters of choice for viewing nebulae, and to some degree supports the general recommendation that if only one filter can be purchased, it should
be the UHC.

In performance characteristics, the UHC filter tends to reveal a
slightly larger and/or brighter area of nebulosity with many emission nebulae than the OIII does, while the OIII filter will often yield somewhat more contrast and dark detail on a given object.

The OIII also tended to be a bit
better for "blinking" small planetary nebulae than the UHC was, while the
H-beta often hurt the view of many planetaries. The inclusion of some
planetary nebulae may have slightly inflated the score of the OIII filter,
since in general, the OIII often does a bit better on those objects. The
H-Beta tended to be most useful on a more limited number of objects (about
16.7 % of the 90 objects surveyed) than either the UHC or the OIII filters.

This may be due at least in part to the fact that many of the so-called
"H-beta objects", are low exitation very faint nebulae, and thus are near or beyond the visual limits of my ten inch.

The Deep-Sky filter almost always
produced at least some gain in contrast for nearly every object observed(especially when some skyglow was present), but rarely produced a spectacular improvement of the view. However, for "mixed" nebulae (ie: reflection and emission objects), the Deep-Sky can be the filter of choice.

Filter comparison results for each of the objects observed are shown below.

-------------------------- SPECIFIC OBJECT RESULTS ---------------------------
Each object is listed with the various filters. Each filter's numerical
score (0, 1, 2, 3, 4, 5; see earlier comments) is given, followed by the
overall filter recommendation for the specific object.

In the RECOMMENDATIONS portion, a "/" between the two filters named indicates that both filters will
work well on the object, with the one on the left side of the slash being a
slightly better choice: ie: "UHC/OIII" means the UHC is slightly better
overall, but the OIII will be quite useful as well.

M1 CRAB NEBULA (SNR in Taurus)
DEEP-SKY: (3) Improves the contrast and brings out the wispy arc-like cusp on
the eastern end.
UHC: (4) Darkens the background and reveals little hints of tattered detail on
the edges with the eastern "cusp" now more visible.
OIII: (3) Much darker than in UHC, and appears slightly smaller and somewhat
rounder, but with hints of filamentary detail on the edges and across the
nebula at moderate powers.
H-BETA: (0) barely visible.
RECOMMENDATION FOR M1: UHC/DEEP-SKY (H-beta *not* recommended).

M8 LAGOON NEBULA (diffuse Nebula in Sagittarius).
DEEP-SKY: (3) Some increase in contrast, with a bit more nebulosity
visible than without a filter.
UHC: (5) Large boost in contrast and visiblity of outer nebulosity. Nebula
appears much larger (nearly a degree wide) with some detail enhancement,
especially in the outer regions.
OIII: (5) Slightly fainter than in the UHC, but shows slightly more contrast
and dark detail than UHC does. Some of the outermost nebulosity fades, but
detail in inner regions is remarkable. Faint red color can be noted in the
brighter areas. May be the better filter under light polluted conditions.
H-BETA: (2) Dims the nebula considerably, with only the circular ball of haze
around the Hourglass nebula and the external arc being easy to see.

M16 EAGLE NEBULA (diffuse nebula in Serpens).
DEEP SKY: (2) Faint diffuse nebulosity is slightly easier to see than without
a filter. Not a great deal of detail visible in nebula.
UHC: (4) Large increase in visible nebulosity, showing wide diffuse fan of
light in the shape of a broad "T". Small darker inclusion becomes visible
along the northern side.
OIII: (4) Slightly fainter than with UHC, with slightly less faint outer
nebulosity, but shows more contrast and dark detail in the interior,
including faint narrow "fingers" from south side into the center of the
nebula with averted vision.
H-BETA: (2) Dims the nebula significantly, but "T" shape still vaguely
RECOMMENDATION FOR M16: UHC/OIII, but H-BETA hurts the view.

M17 SWAN (OMEGA) NEBULA (diffuse nebula in Sagittarius).
DEEP-SKY: (3) Some improvement in contrast and detail, with the fainter
loop of nebulosity to the northeast just becoming visible to form the omega
UHC: (4) Noticable improvement in contrast and detail, with much of the faint
nebulosity on the outer regions and along the "omega" loop becoming quite
easy to see.
OIII: (5) Slightly fainter than UHC, but contrast is also higher, with a
rather striking dark area becoming noticable along the west side of the swan's
neck. Dark detail in interior of main bar is better defined than with UHC.
H-BETA: (1) Object is noticably dimmed compared to the other filters, making
the filter a poor choice for use on M17.

M20 TRIFID NEBULA (diffuse emission/reflection nebula in Sagittarius)
DEEP-SKY: (2) Small difference between filtered and unfiltered views with a
slight gain in contrast with the filter, but with any light pollution, the
filter may be of greater use.
UHC: (4) Nebula is slightly fainter than with DEEP-SKY filter, with a slight
gain in contrast over the DEEP-SKY and more contrast gain over unfiltered
OIII: (3) Nebula is fainter than with UHC or DEEP-SKY, and main trifid section
appears slightly smaller (hurts the northern reflection nebulosity), but dark
detail in the inner "lanes" shows up slightly better.
H-BETA: (4) Nebula is somewhat fainter than in UHC, but trifid section shows
a bit larger area of nebulosity than the UHC does. It kills the reflection
nebula and reduces the brightness of the detail right around the central star.

M27 DUMBELL NEBULA (planetary nebula in Vulpecula)
DEEP-SKY: (3) Some improvement in visibility of outer haze off the sides of
the dumbell, but the object is also slightly fainter.
UHC: (5) Large improvement in contrast and outer detail, with large "wings" of
light off the Dumbell's sides becoming easy to see. Interior seems brighter
and bigger, with interesting greenish glow.
OIII: (4) Dimmer than with UHC, but interior shows more dark detail and
contrast. "Wings" off the sides remain fairly easy to see.
H-BETA: (1) Nebula is dimmed greatly by the filter, extinguishing the fine
outer detail and only showing the inner dumbell-shape.
RECOMMENDATIONS FOR M27: UHC (OIII also useful in showing some inner detail,
but H-BETA is NOT recommended).

M42 GREAT ORION NEBULA (diffuse nebula)
DEEP-SKY: (3) A moderate boost in contrast can be seen, and much more
outlying nebulosity is visible. This is a good filter for the general
public, since it still will show the stars while enhancing the nebula.
UHC: (5) Large boost in contrast over no filter is noted. Outer nebulosity is
quite easy to see, with southward loop being easily seen with averted vision.
Bluish and greenish colors are quite easy to note with direct vision.
OIII: (4) A few of the outermost nebulosity areas are dimmed, but there is
more contrast, with considerable improvement in light and dark detail,
especially in the inner regions. Bluish and occasionally, reddish tints are
noted with large apertures. M43 is somewhat fainter than in the UHC filter,
but narrow bandwidth of OIII may make it the filter of choice with light
H-BETA: (3) Much of the fainter outer areas of the nebula vanish, but fan-like
main portion and M43 remain, with interesting contrast and changes in detail
visible, including a brighter linear arc in the western part of the fan.
Some reddish hints are also visible in the H-beta.

M43 (north part of Great Orion Nebula).
DEEP-SKY: (3) higher contrast than without filter, but not much detail
enhancement except when there is some light pollution.
UHC: (3) somewhat more contrast than with the Deep-Sky with overall "comma"
shape now easily seen.
OIII: (2) dims the nebula, but overall shape is still easily visible.
H-BETA: (4) Really makes M43 stand out, with high contrast and some irregular
dark detail in the overall comma-shaped nebula.
RECOMMENDATION FOR M43: H-BETA (UHC and Deep-Sky also help).

M57 RING NEBULA (planetary nebula in Lyra)
DEEP-SKY: (2) Darkens the background slightly, and brings out hints of
very faint nebulosity off the ends of the oval, but otherwise doesn't help
UHC: (4) Really darkens the background and stars, and begins to show a more
prominent glow in the interior of the ring, with hints of faint outer
nebulosity around the outer edges of the ring.
OIII: (4) Darkens the nebula and the background still further, but slight
increase in contrast noted. Outer shell just visible with averted vision.
H-BETA: (0) Really kills things, with the nebula now being very dim.
RECOMMENDATIONS FOR M57: UHC/OIII. Nebula is bright and small enough not to
really benefit enormously from filter use, but UHC does improve it to a
degree (H-BETA is NOT recommended!).

M76 "MINI-DUMBELL" or BUTTERFLY NEBULA (planetary nebula in Perseus):
DEEP-SKY: (2) Marginal improvement over no filter, with hints of nebulosity
off the sides of the dumbell.
UHC: (4) Much more nebulosity visible, including faint patches or "wings" off
each side of the dumbell, along with some interior detail.
OIII: (4) Nebula is slightly fainter, but shows more contrast, with some dark
detail being seen near each lobe of the dumbell. The patches off to the sides
of the dumbell look like partial loops.
H-BETA: (0) Dims the nebula almost to extinction at moderate powers.

M97 "OWL NEBULA" (planetary nebula in Ursa Major):
DEEP-SKY: (2) Slight improvement over non-filter use (hints of the "eyes").
UHC: (4) Much higher contrast than with Deep-Sky filter. One eye and hints
of the other are seen.
OIII: (5) Increase in contrast over UHC. Both eyes visible with hints of
irregular outer edge structure.
H-BETA: (0) Nearly obliterates the nebula.
RECOMMENDATION FOR M97: OIII/UHC (H-beta *not* recommended).

NGC 40 (Planetary Nebula in Cepheus):
DEEP-SKY: (3) Slight increase in contrast and detail (brighter opposing
sides), but object does not really require a filter.
UHC: (3) Slightly fainter than in Deep-sky, but shows a bit more contrast.
OIII: (2) Somewhat fainter than in UHC, but disk still quite visible.
H-BETA: (2) Somewhat fainter than in UHC, but very slightly brighter than
with the OIII filter (a "near" H-beta object).

NGC 246 (Planetary in Cetus):
DEEP-SKY: (2) defines it a bit better than without a filter, but still mainly
a diffuse roughly circular glow around a few stars.
UHC: (3) Higher contrast, with nebula now a fairly well-defined moderate-sized
dim disk with hints of brightness variations in the interior.
OIII: (5) Dramatic increase in contrast over the UHC! Shows several dark
spots in the interior and hints of sharp filament-like outer edge of the disk.
H-BETA: (0) Really kills the nebula (barely visible).
RECOMMENDATION FOR NGC 246: OIII. (H-Beta *not* recommended).

NGC 281 (Diffuse emission nebula (Cassiopeia):
DEEP-SKY: (3) Nebula is somewhat easier to see (barely visible without
filters), with the edges being more defined.
UHC: (4) Noticable improvement in contrast and detail, appearing larger than
with Deep-Sky filter, and containing some dark detail.
OIII: (4) Nebula is dimmer, but interior dark lane-like detail becomes more
noticable, and the overall nebula shape is better defined than in UHC.
H-BETA: (2) Dims the nebula much more than OIII, with no more detail than is
seen with the Deep-Sky filter (dim).

NGC 604 (HII region in galaxy M33 in Triangulum).
DEEP-SKY: (2) slight increase in contrast over unfiltered view, but easy to
see without filters.
UHC: (3) Much easier to see than in Deep-sky, standing out well as an oval
puff, with much of the detail in the galaxy remaining visible.
OIII: (4) Considerable increase in contrast, almost "blinking" over UHC and
unfiltered views. Galaxy is much fainter, but nebula really stands out.
H-BETA: (2) Much dimmer than in the other filters, but nebula is still seen.

NGC 896/IC 1795 (diffuse nebula in Cassiopeia).
DEEP-SKY: (3) noticable increase in visiblity, with nebula being only a glow
without the filter. Two areas of dim diffuse nebulosity seen, one large
(IC 1795) and the other smaller (NGC 896).
UHC: (4) Much more prominent, with better definition and a little dark detail,
along with a wispy outer arc curving around from south part of IC 1795.
OIII: (4) Dimmer than in UHC, but more dark detail visible with faint outer
loop-like structure visible arcing south, almost connecting the two patches.
H-BETA: (1) Barely visible.
RECOMMENDATION FOR NGC 896/IC 1795: UHC/OIII (H-beta *not* recommended).

NGC 1360 (large Planetary Nebula in Fornax).
DEEP-SKY: (2) slight increase in contrast with nebula easier to see than
without a filter (but still visible without a filter).
UHC: (4) Significant improvement in contrast, with nebula appearing larger and
noticably oval. Some irregular interior detail and central star noted.
OIII: (4) Even more contrast than UHC, with clear interior arc-like detail,
but central star much fainter. Nice dark background
H-BETA: (0) Kills the nebulosity with only the central star and a small hint
of haze around the star being visible.
RECOMMENDATION FOR NGC 1360: OIII/UHC (H-beta *not* recommended).

NGC 1491 (diffuse Nebula in Perseus).
DEEP-SKY: (3) moderate increase in contrast over non-filtered view.
UHC: (5): larger, with faint irregular outer nebulosity seen and bar-like
inner feature now very obvious.
OIII: (4): Higher contrast in inner regions (especially the bar), but outer-
most nebulosity dimmed.
H-BETA: (0), kills most of the nebulosity other than a hint of it.
RECOMMENDATION FOR NGC 1491: UHC/OIII (H-Beta *not* recommended).

NGC 1499 CALIFORNIA NEBULA (diffuse Nebula in Perseus). Without filters,
the nebula is barely visible as a faint brightening of the field with no
DEEP-SKY: (2) A slight increase in contrast was noted, but otherwise,
the view was similar to that without a filter.
UHC: (2) Slight increase in contrast over the Deep-Sky filter, making the
edges of the nebula slightly easier to see, but nebula is still somewhat
difficult. Hints of vague brightness variations across the object are noted.
OIII: (1) Nebulosity is quite dim in a very dark field.
H-BETA: (4) Dramatic increase in contrast noted, making the object fairly easy
to notice, with well-defined borders. Some faint filamentary detail is also
noted. California Nebula is visible to unaided eye when H-beta is used.

NGC 1514 "CRYSTAL-BALL NEBULA" (planetary nebula in Taurus):
DEEP-SKY: (2) Nice faint round puff around a faint star, easier to see
than without a filter.
UHC: (4) Significant improvement in contrast, well-defined hazy ball with
hints of dark detail in the interior of the nebula.
OIII: (4) More contrast than in UHC, with dark detail and arc-like forms in
the main shell. Dimmer than in UHC but a bit better overall.
H-BETA: (0) Almost wipes out the nebula.

NGC 1999 (diffuse nebula in Orion):
DEEP-SKY: (2) slight enhancement over no filter, and easy without one.
UHC: (1) fainter than Deep-Sky or no filter.
OIII: (1) fainter than UHC or Deep-Sky.
H-Beta: (1) fainter than Deep-Sky, UHC, or no filter.

NGC 2022 (planetary nebula in Orion):
DEEP-SKY: (3) visible without a filter, but stands out better with Deep-sky
(small fuzzy disk).
UHC: (4) Noticably improves the contrast, with an almost annular form visible
at higher magnifications.
OIII: (5) Much higher contrast and darker background than in UHC, but UHC or
no filter may be bit better for high power observations of details.
H-BETA: (0) Almost wipes it out (barely visible).

NGC 2024 "FLAME NEBULA" (diffuse emission/reflection nebula in Orion)
DEEP-SKY: (3) Noticably improves the contrast with the dark lane-like detail
UHC: (3) Darker than in Deep-sky but with only a slight increase in contrast.
OIII: (2) Darker than in UHC, with less detail than in UHC.
H-BETA: (1) Darkest of all three filters, but the nebula remains visible with
detail similar to that of OIII.

NGC 2174 (diffuse nebula in northern Orion).
DEEP-SKY: (2) very faint glow around a single star with hints of detail (much
easier to see than without a filter).
UHC: (4) Large increase in contrast over Deep-Sky filter, showing a large
circular area of haze with vague irregular interior dark detail.
OIII: (4) Dimmer than in UHC, but has more contrast, showing some dim lane-
like structure.
H-BETA: (0) Dims the nebula almost to extinction, showing less than the Deep-
RECOMMENDATION FOR NGC 2174: UHC/OIII (near tie) (H-Beta NOT recommended).

NGC 2327 (diffuse nebula in Monoceros).
DEEP-SKY: (2) Very faint diffuse roughly circular haze around 7th mag. star.
UHC: (3): Object is larger with slightly better definition than in Deep-sky.
OIII: (2): nebula is now very faint, with only the area round the star visible.
H-BETA: (4): object is not quite as bright as in UHC but is *much* better
defined, showing a dark inclusion from the northeast and a brighter arc-like
western edge.

NGC 2237-9 "ROSETTE NEBULA" (diffuse nebula in Monoceros).
DEEP-SKY: (2) Some increase in contrast, but nebula is still more of a diffuse
haze around the central star cluster with hints of irregularity.
UHC: (5) Noticable increase in contrast, with more outer nebulosity visible
and some irregular light and dark structure being visible. Nebula was visible
when UHC was held up to unaided eye!
OIII: (5) Higher contrast than with UHC, with more dark irregular detail
throughout the region, but not quite as much nebulosity visible as in UHC.
H-BETA: (1) Very faint glow around the star cluster, not much better than
without a filter (but much dimmer).

NGC 2264, "CONE NEBULA" near S Monocerotis.
DEEP-SKY: (2) slight increase in contrast, with dim diffuse haze now visible
and brightest spot WSW of S Mon.
UHC: (4) Faint nebulosity now visible over entire field, nearly a degree wide.
Dark southern inclusion "Cone" faintly visible in southern part of nebula.
OIII: (3) Dimmer than in UHC, with only the area southwest of S Mon being easy
to see (Cone not visible).
H-BETA: (1) Only a hint of a glow southwest of S Mon.

NGC 2346 (Planetary nebula in Monoceros):
DEEP-SKY (2): slightly easier to see than without a filter.
UHC: (3) some increase in contrast, with hints of annularity.
OIII: (3) some increase in contrast, slightly fainter than in UHC.
H-BETA: (0) nearly extinguished.
RECOMMENDATION FOR NGC 2346: UHC/OIII (near tie) (H-beta *not* recommended).

NGC 2438 (planetary nebula in Puppis).
DEEP-SKY (2) noticably easier to see than without a filter. Hints of
UHC: (3) notable increase in contrast, easier to see than in Deep-sky with
annular form more noticable.
OIII: (4) much higher in contrast with annular form now fairly obvious.
H-BETA: (0) nearly kills it completely.
RECOMMENDATION FOR NGC 2438: OIII (H-Beta *not* recommended).

NGC 2359 THOR'S HELMET (diffuse nebula in Canis Major).
DEEP-SKY: (2) Better defined than without a filter but still low in contrast.
UHC: (4) Higher contrast than in Deep-sky, with arc like detail off of a
central oval ring-like mass.
OIII: (5) even more contrast than in UHC with oval mass now looking like a
loop with tendrils off each end.
H-BETA: (0) Kills most of the nebulosity.
RECOMMENDATION FOR NGC 2359: OIII/UHC (H-Beta *not* recommended).

NGC 2467 (diffuse nebula in Puppis).
DEEP-SKY: (2) Sparse star cluster with a single star and a faint ball of haze
around it which is brighter on the south side.
UHC: (4) Much more contrast and detail than in Deep-Sky with brighter linear
band or patch on south side.
OIII: (5) More contrast and detail than in UHC with the arc connected to a
"loop" which runs through the central star. Faint hints of outer detail.
H-BETA: (1) Really dims it.
RECOMMENDATION FOR NGC 2467: OIII/UHC (H-Beta *not* recommended).

NGC 2371-2 (planetary nebula in Gemini).
DEEP-SKY: (2) Two adjacent faint spots, helped somewhat over non-filter use.
UHC: (4) enhanced over Deep-Sky, with the two lobes showing hints of contact.
OIII: (4) Slightly higher contrast than UHC. Hints of faint outer wings.
H-BETA: (0) Kills the nebulosity.
RECOMMENDATION FOR NGC 2371-2: OIII/UHC (near tie) (H-Beta *not* recommended)

NGC 2392 "ESKIMO NEBULA" (planetary nebula in Gemini)
DEEP-SKY: (2) enhanced slightly over non-filter use (easier to see the outer
of the two shells).
UHC: (4) Darkens the sky background and enhances the nebula, making both
shells quite easy to see.
OIII: (4) Jet-black sky background with higher contrast than UHC, but the two
shells almost seem to merge (tones down the central star).
H-BETA: (0) Only the inner shell is visible, much fainter than in UHC, OIII,
or Deep-Sky.
RECOMMENDATION FOR NGC 2392: OIII/UHC. (H-Beta *not* recommended).

NGC 3242 "GHOST OF JUPITER" (planetary in Hydra).
DEEP-SKY: (2) slightly enhanced over non-filter use (easy without filters).
UHC: (4): much higher contrast with faint circular outer halo-like shell
beyond the two inner shells now visible.
OIII: (4): much darker background but the two inner shells really blaze out.
H-BETA: (1): much fainter (only the innermost shell is easily seen).
RECOMMENDATION FOR NGC 3242: UHC/OIII (near tie) (H-Beta not recommended).

NGC 4361 (planetary nebula in Corvus):
DEEP-SKY: (2) somewhat higher contrast than without a filter.
UHC: (4) Large increase in contrast with faint diffuse outer extensions seen.
OIII: (4) Higher contrast, a bit sharper than in UHC but nebula appears
slightly smaller.
H-BETA: (0): nearly killed by the filter.
RECOMMENDATION FOR NGC 4361: UHC/OIII (near tie), (H-Beta *not* recommended).

NGC 6210 (planetary nebula in Hercules).
DEEP-SKY: (2) stands out a bit better, but filters are not needed.
UHC: (4) increase in contrast with faint hints of close outer shell north
and south of main disk.
OIII: (4) darkens the background and also shows hints of the outer shell.
H-BETA: (1) dims the nebula, showing only the brighter inner core.
RECOMMENDATION FOR NGC 6210: OIII/UHC (H-Beta *not* recommended).

NGC 6302 "BUG NEBULA" (planetary nebula in Scorpius).
DEEP-SKY: (2) somewhat more contrast than without a filter.
UHC: (3) noticable improvement in contrast with central core region now
seeming much brighter and outer E-W flarings much easier to see.
OIII: (3) makes the core region really stand out, although the nebula is not
quite as bright as in the UHC.
H-BETA: (0).
RECOMMENDATION FOR NGC 6302: OIII/UHC (H-Beta *not* recommended).

NGC 6334 (diffuse nebula in Scorpius).
DEEP-SKY: (2) nebula is a large very faint glow which is brightest around one
star near the south end.
UHC: (4) two separated patches around two stars near the south end, plus
fainter patches and dark spots visible in a dim diffuse haze to the north.
OIII: (3) fainter than in UHC, but still visible.
H-BETA: (3) similar to OIII view but slightly fainter.
RECOMMENDATION FOR NGC 6334: UHC (OIII and H-beta also useful).

NGC 6445 (Planetary Nebula in Sagittarius).
DEEP-SKY: (2) makes it stand out better.
UHC: (4) noticably improves the contrast over Deep-Sky.
OIII: (3) darker more contrasting field, but slightly fainter than UHC.
H-BETA: (0) kills the nebula almost completely.
RECOMMENDATION FOR NGC 6445: UHC/OIII (H-beta *not* recommended).

NGC 6357 (diffuse nebula in Scorpius).
DEEP-SKY: (2) not easy to see without a filter, as Deep-Sky just barely
brings it out.
UHC: (3) Noticable boost in contrast, showing some irregularity and a brighter
portion around a tiny group of stars.
OIII: (4) More contrast than UHC, with the patch around the tiny star group
greatly enhanced.
H-BETA: (1) almost kills the nebulosity.
RECOMMENDATION FOR NGC 6537: OIII/UHC (H-Beta *not* recommended).

NGC 6543 "CAT'S EYE" (planetary nebula in Draco).
DEEP-SKY: (2) makes it stand out better.
UHC: (4) noticable contrast improvement with faint diffuse outer halo visible.
Faint patch west of main nebula barely visible (IC 4677).
OIII: (4) really darkens the background and boosts the visibililty of the
outer halo. IC 4677 now slightly easier to see.
H-BETA: (1) really dims it but is still visible.
RECOMMENDATION FOR NGC 6543: OIII/UHC (H-Beta *not* recommended).

NGC 6559/IC 4685 (diffuse nebula in Sagittarius).
DEEP-SKY: (2) not visible without filters, glow around one star with hints
of extensions north and northwest.
UHC: (4), noticably enhanced with some light and dark structure.
OIII: (2) still visible but much fainter than in UHC.
H-BETA: (2) visible with slight structure.

NGC 6781 (planetary in Aquila).
DEEP-SKY: (3) easy without a filter but shows more contrast with hints of
annularity even at low power.
UHC: (4) noticable boost in contrast with strong annular form and glowing
interior (notable brightening along south side).
OIII: (4) really darkens field and enhances the annularity.
H-BETA: (0) kills the nebula completely.
RECOMMENDATION FOR NGC 6781: OIII/UHC (H-beta *not* recommended).

NGC 6804 (Planetary nebula in Aquila).
DEEP-SKY: (2) slightly easier to see than without a filter.
UHC: (3) brings the nebula out well.
OIII: (4) nice high contrast a bit better than UHC.
H-BETA: (0), nearly wipes it out.
RECOMMENDATION FOR NGC 6804: OIII/UHC (H-beta *not* recommended).

CRESCENT NEBULA (NGC 6888) (diffuse nebula in Cygnus).
DEEP-SKY: (2) slight improvement over no filter, with the brightest
segment of the crescent going through a star along the northern end of the
nebula fairly easy to see.
UHC: (4) Nebula is now much easier to see, appearing as a large nearly
complete oval ring of dim nebulosity with brightness variations and a dimly
glowing interior.
OIII: (5) Complete oval ring with glowing interior and slightly higher
contrast than with UHC, but overall nebulosity is fainter than with UHC.
H-BETA: (1) Very dim, with only the brightest arc portion which was seen in
the Deep-Sky filter visible at all in a very dark field. Nebula almost gone.
RECOMMENDATION FOR NGC 6888: OIII/UHC (near tie). H-beta *not* recommended!)

VEIL NEBULA NGC 6960-95 (SNR in Cygnus).
DEEP-SKY: (3) Nebula is easier to see than without a filter, with both sides
of the loop being visible, including the section through 52 Cygni.
UHC: (4) Large increase in detail and contrast! Nebula really stands out with
some filamentary detail. Hints of other strands in the interior of the loop.
filaments and strands visible even between the two main arcs, making the
entire complex closely resemble its photograph. OIII is the filter of choice
H-BETA: (1) Very dim, but still visible (forget it!).
RECOMMENDATIONS FOR VEIL: OIII (UHC is helpful, but not quite as much as the
OIII: H-BETA is NOT recommended).

NORTH AMERICAN NEBULA NGC 7000 (diffuse nebula in Cygnus).
DEEP-SKY: (2) Nebular overall form is easier to see than without a filter, but
only slightly.
UHC: (5) Very noticable improvement in contrast over the DEEP-SKY filter, with
both "Florida" and "Mexico" now quite easy to see.
OIII: (4) Some improvement in contrast and detail, with brighter "spine" on
east side of "Mexico" and some faint dark detail being easy to see, but
nebula is somewhat fainter than in UHC.
H-BETA: (3) Detail is similar to OIII, but nebulosity is fainter than OIII.
RECOMMENDATIONS FOR NGC 7000: UHC/OIII but both H-BETA/Deep-Sky are useful on
the object (UHC was brighter, but OIII shows more contrast).

NGC 7008 (planetary nebula in Cygnus).
DEEP-SKY: (2), slight increase in contrast, showing the irregular form.
UHC: (4): real boost in contrast with detail now visible.
OIII: (5): slightly higher contrast than UHC, and works at high power.
H-BETA: (0): nearly obliterates the object.
RECOMMENDATION FOR NGC 7008: OIII/UHC (H-Beta *not* recommended!).

NGC 7009 SATURN NEBULA (planetary nebula in Aquarius).
DEEP-SKY: (2) does show the anses on each end of the planetary a bit better,
in the form of two small puffs.
UHC: (4) Anses become more spike-like, with noticable increase in contrast.
OIII: (4) Nebula is dimmer, but contrast is a bit higher, especially in the
interior, where inner shell detail can be seen.
H-BETA: (1) Nebula is noticably dimmer, appearing as just a disk.
RECOMMENDATION FOR NGC 7009: Filters are not needed, but OIII/UHC will help
bring out the fainter detail (H-BETA not recommended).

NGC 7023 Emission/reflection Nebula in Cepheus.
DEEP-SKY: (3) Noticable boost in contrast with nebular glow expanded over no
filter. Darker areas noted on east and west sides.
UHC: (2) dimmer than in Deep-sky and slightly smaller, but nebula still shows
up better than without a filter.
OIII: (2) dimmer than in UHC but still shows some hints of detail.
H-Beta: (1) dimmer than UHC and OIII. Only central area around the star
remains visible.

NGC 7026 (Planetary nebula in Cygnus)
DEEP-SKY: (2) Slight boost in contrast.
UHC: (3) not a lot better than in Deep-sky filter (dumbell or bipolar).
OIII: (3) slightly darker sky background but not much better than UHC.
H-BETA: (0) much fainter than without a filter.
RECOMMENDATION FOR NGC 7026: OIII/UHC *near tie* (H-Beta *not* recommended).

NGC 7027 (Planetary nebula in Cygnus).
DEEP-SKY: (2) easy without filter, but Deep-Sky makes it stand out a little
better as a small bluish-green oval.
UHC: (4) really makes the nebula almost blaze out and hints at large faint
irregular outer shell. High power reveals off-center central star and an
interior arc southeast of the central star.
OIII: (4) Core slightly dimmer than in UHC, but outer shell is easier to see
with hints of detail in the outer shell.
H-BETA: (0) Really dims the nebula!
RECOMMENDATION FOR NGC 7027: OIII/UHC *near tie* (H-BETA not recommended!).

NGC 7048 (Planetary nebula in Cygnus).
DEEP-SKY: (2) faint but a bit more contrast than without a filter.
UHC: (3) much higher contrast showing a faint glowing oval.
OIII: (4) more contrast than UHC showing darker center and annularity.
H-BETA: (0): nearly kills it.
RECOMMENDATION FOR NGC 7048: OIII/UHC (H-Beta *not* recommended!).

NGC 7129-33 (Diffuse Emission/reflection Nebula in Cepheus)
DEEP-SKY: (2) slight increase in contrast, with a faint haze visible around a
central group of 4 to 6 stars.
UHC: (3) Haze now easier to see with more contrast, but still rather diffuse
with some faint detail which is brightest in the northern portion. Two other
faint patches visible slightly away from the north one.
OIII: (3) Brings out a little more detail (dark inclusion in one side?).
H-BETA: (1) dims the nebula significantly, although it is still there.

NGC 7139 (faint planetary nebula in Cepheus).
DEEP-SKY: (2) increased contrast over non-filter use.
UHC: (3): Still faint, but much easier to see.
OIII: (4): More contrast than UHC.
H-BETA: (0): nebula not visible.
RECOMMENDATION FOR NGC 7139: OIII/UHC (H-Beta *not* recommended).

NGC 7293 GIANT HELICAL NEBULA (planetary nebula in Aquarius).
DEEP-SKY: (2) large dim roughly circular fuzzy patch with slightly darker
middle, easier to see than without a filter, but does not have a lot of
UHC: (4) Noticable increase in contrast, showing a clear fat slightly diffuse
ring with a glowing center and hints of structure. Nebula is now quite easy.
OIII: (5) Much more contrast than the UHC, with hints of helical nature and
indications of outer filamentary nebulosity. Dimmer than in UHC, but stands
out better than in the UHC. Best performance of all the filters.
H-BETA: (0) Barely visible in this filter (almost kills the nebulosity).
RECOMMENDATION FOR NGC 7293: OIII/UHC (H-beta NOT recommended).

NGC 7538 (Diffuse nebula in Cepheus):
DEEP-SKY: (3) boosts the contrast making it easier to see than without a
UHC: (4) darkens the background and brings out the nebulosity more than Deep-
OIII: (4) dimmer, but contrast is a bit higher.
H-BETA: (0) Dims it nearly to extinction.
RECOMMENDATION FOR NGC 7538: UHC/OIII (H-beta NOT recommended).

NGC 7635 BUBBLE NEBULA (diffuse nebula in Cassiopeia).
DEEP-SKY: (2) Vague diffuse oval fuzzy area around a bright star.
UHC. (3) Oval area of nebulosity noted around the star running roughly east-
west with large very dim diffuse extensions noted to the northwest and
southeast. A dim "Y"-shaped patch can also be seen just north of the central star.
OIII: (4) Higher contrast, with the "Y"-shaped patch now much more definite.
H-BETA: (1) Very dim, not as good as OIII, but nebula is still visible.

NGC 7662 BLUE SNOWBALL (planetary nebula in Andromeda).
DEEP-SKY: (2). Deep-sky filter does darken the background somewhat.
UHC: (3) Really darkens the background, but adds only a little nebulosity.
OIII: (3) Dims the nebula slightly, giving a jet black sky background and a
bit more interior contrast (but not much more detail).
H-BETA: (1) Significantly dims the nebula over the OIII.
RECOMMENDATIONS FOR NGC 7662: Filters are not really needed, but UHC/OIII
may help with locating it at low power via "blinking" (H-BETA is not

NGC 7822 (faint diffuse nebula in Cepheus).
DEEP-SKY: (2) Very faint large elongated (east-west) glow around a few stars.
UHC: (3) Glow is noticably enhanced over Deep-sky, shows some irregularity.
OIII: (2) Fainter than UHC, but still visible.
H-BETA: (2) fainter than the UHC, but shows about as much detail as UHC.
RECOMMENDATION FOR NGC 7822: UHC (H-Beta and OIII also useful).

IC 405 FLAMING STAR NEBULA (diffuse emission/reflection nebula in Auriga).
DEEP-SKY: (3) Nebula visible as a very faint diffuse glow with irregularities
around and to the east of AE Aur. Not clearly visible without filters.
UHC: (2) Slight increase in contrast showing faint arc-like filament north-
east of AE. Faint background glow fainter than in Deep-Sky filter.
OIII: (1) Only hints of nebulosity.
H-BETA: (2) Hints of arc and one other faint patch north of AE but nebula is
fainter than in UHC or Deep-Sky.
RECOMMENDATION FOR IC 405: DEEP-SKY/UHC (no filter helps a lot, and may be
mostly a reflection nebula).

IC 410 (Nebula assoc. with NGC 1893 in Auriga)
DEEP-SKY: (2) faint glow running E-W through the "Y"-shaped cluster NGC 1893
with southward extension off east end.
UHC: (4) detailed arc-like irregular nebulosity running east-west and then
curving south with darker inclusion along southwest side.
OIII: (4) Brings out more dark detail along the east and south sides, but
nebula is dimmer. Really stands out, as nebula follows the form of the
H-BETA: (0) Nebula is almost wiped out.
RECOMMENDATION FOR IC 410: OIII/UHC. (H-beta *not* recommended).

IC 417 (diffuse Nebula in Auriga)
DEEP-SKY: (2) Nebula is now barely visible around cluster Stock 8
UHC: (3) increase in contrast over DS filter.
OIII: (3) darker background
H-BETA: (4) more contrast and a bit more nebulosity visible.

IC 434 HORSEHEAD NEBULA (diffuse nebula in Orion).
DEEP-SKY: (2) Little change is seen from viewing without a filter.
When visible, it appears as a weak dark gap in the dim north-south nebulosity,
and the shape is hard to see. Nebula is difficult, unless viewed under very
dark and clear conditions.
UHC: (3) Horsehead now stands out weakly, showing some of the horsehead shape
with averted vision, a definite improvement over no filter or the DEEP-SKY.
OIII: (0) No Horsehead seen. IC-434 nebulosity not seen for certain.
H-BETA: (4) Nebula still dim, but Horsehead shape now fairly easy to see,
showing up with more contrast than with the UHC filter. East edge of IC 434
seems brighter than the rest of the nebula with the H-beta.

IC 1318 GAMMA CYGNI NEBULA (diffuse nebula in Cygnus).
DEEP-SKY: (2) Brings out a large faint diffuse nebulosity in two elongated
segments with a darker area between them east of Gamma Cygni.
Larger area well northwest of Gamma also visible.
UHC: (3) Increase in contrast noted over Deep-sky filter, with dark gap
between the patches east of Gamma Cygni now much more notable.
OIII: (1) Filter almost extinguishes the nebulae (very faint).
H-BETA: (3) Nebula is fainter than in UHC, but has higher contrast with a very
dark sky background in the areas around the nebulosity.
RECOMMENDATION FOR IC 1318. H-BETA/UHC (near tie) (OIII *not* recommended)

IC 1396 (nebula S.W. of Mu Cephei).
DEEP-SKY: (2) Diffuse haze around a weak open star cluster, quite large with
some vague brightness irregularities and a possible dark inclusion in the
south side (B161).
UHC: (3) Nebulosity more visible and dark inclusion is much more definite, but
the glow is still faint. Some variations in brightness are noted, but the
object is still rather diffuse.
OIII: (2) Dimmer than in UHC, with outermost nebulosity gone, but some more
contrast and dark detail are noticable (better than in Deep-Sky filter).
H-BETA: (1) Nebulosity is visible, but is *extremely* dim in a dark

IC 1848: (Diffuse Nebula, Cassiopeia).
DEEP-SKY: (2) some increase in contrast with nebula appearing as an elongated
faint haze going through a sparse cluster.
UHC: (4) Much easier to see, with nebula now elongated E-W, brighter on
northern side.
OIII: (4) noticably darker than UHC, but a little higher contrast.
H-BETA: (1) Very dim.
RECOMMENDATION FOR IC 1848: UHC (H-beta *not* recommended)

IC 2177: (Diffuse Nebula, Monoceros).
DEEP-SKY: (2) long faint irregular diffuse band of haze not easily seen
without filters. Extends southward from open cluster NGC 2235.
UHC: (3) Easier to see, with somewhat more contrast. Narrower slightly
sinuous core filament imbedded in more diffuse haze visible for nearly 2
OIII: (2) Nebula barely visible, with most of outlying nebulosity gone.
H-BETA: (3) Core filament is fainter than UHC, but considerably more contrast.

IC 4628 (diffuse nebula in Scorpius):
DEEP-SKY: (2) faint diffuse irregular glow not visible without filters.
UHC: (4): Noticable improvement, with nebula now easy to see and rather
detailed, with some irregular lane-like detail.
OIII: (2): much fainter than in UHC, but still visible.
H-BETA: (3): shows some interesting filamentary detail, but not as bright or
as detailed as in UHC.

IC 5067-70 PELICAN NEBULA (diffuse nebula in Cygnus):
DEEP-SKY: (2) Nebular overall form is easier to see than without filters, with
some hints of detail and the overall form.
UHC: (4) Very noticable improvement in contrast over the DEEP-SKY filter, with
both the "beak" and the "body" now fairly easy to see.
OIII: (4) Improvement in contrast and detail, but nebula is dimmer than UHC.
H-BETA: (2) Nebulosity is visible but is very faint.
RECOMMENDATIONS FOR IC 5067: UHC/OIII, Deep-sky also useful on the object
(UHC was brighter, but OIII shows more detail).

IC 5146 THE COCCOON NEBULA (diffuse nebula in Cygnus).
DEEP-SKY: (2) A bit better than no filter, but object is still easily seen as
a dim roughly circular irregular patch in some stars without a filter.
UHC: (3) Slightly higher contrast with more irregular interior dark detail.
OIII: (1) Fainter and slightly smaller than in UHC (OIII hurts it).
H-beta: (3) dimmer than UHC but shows larger area of outer nebulosity and
slightly better defined dark detail in the form of irregular lane like
RECOMMENDATIONS FOR IC 5146: H-BETA/UHC *near tie* (OIII not recommended).

PK64+5.1 "CAMPBELL'S HYDROGEN STAR" Cygnus (Henize 2-438, PNG 64.7+5.0)
DEEP-SKY: (2) only slight increase in contrast (small nearly stellar
UHC:(3): Slight increase in contrast with faint outer shell hinted at.
OIII: (2) dimmer than UHC, but slightly more contrast than without filters.
H-BETA: (4) Noticable increase in contrast with very faint outer shell.

PK205+14.1 "MEDUSA NEBULA" (large planetary nebula in Gemini):
DEEP-SKY: (2) Slight increase in contrast but nebula is still just a very
faint diffuse hazy area.
UHC: (3) noticable increase in contrast with vague "C" shaped arc now visible.
OIII: (4) dimmer than in UHC, but slightly more contrast, with hints of
filaments in the dark part (looks almost annular).
H-BETA: (0) Completely kills the nebula.
RECOMMENDATION FOR PK204+14.1: OIII/UHC *near tie* (H-beta *not* recommended).

PK164+31.1 "HEADPHONE NEBULA" (large planetary nebula in Lynx).
DEEP-SKY: (2) Very slight increase in contrast over non-filtered view.
UHC: (3) noticably easier to see as two spots connected by a vague annulus.
OIII: (3) much easier to see the spots, but the annulus fades somewhat.
H-BETA: (0) Completely kills the nebula.
RECOMMENDATION FOR PK164+31.1: UHC/OIII *near tie* (H-beta *not* recommended).

Sh2-13 (Diffuse nebula in Scorpius).
DEEP-SKY: (2) dimly visible as a very faint glow but not without the filter.
UHC: (4) boost in contrast, becoming very patchy but still dim.
OIII: (2) fainter but still visible.
H-BETA: (2) similar to OIII.

Sh2-54 (Diffuse nebula in Serpens).
DEEP-SKY: (2) dim diffuse glow not visible without filters.
UHC: (4) noticable contrast gain, with considerable light and dark detail.
OIII: (2) much fainter than in UHC but still visible.
H-BETA: (3) better than in OIII with a little detail.

Sh2-84 (Diffuse nebula in Sagitta).
DEEP-SKY: (1): only hint of nebula.
UHC: (3): faint diffuse "L"-shaped patch with irregular edges.
OIII: (1): dark field with just a hint of nebulosity.
H-BETA: (2): fainter than in UHC.

Sh2-101 (Diffuse Nebula in Cygnus): Only hinted at without filters.
DEEP-SKY: (2) Very faint moderate-sized diffuse haze in two segments around 3
stars (2 stars on the west and one on the east).
UHC: (3) Higher contrast but still faint. Two definite patches visible with
hazy arc-like extensions. One on the west apppears larger.
OIII: (2) Very dim but still visible.
H-BETA: (3) Almost as much nebulosity visible as in UHC, but dimmer.

Sh2-112 (Diffuse Nebula in Cygnus N.W. of Deneb): hinted at without filters.
DEEP-SKY: (3) faint star with very faint small diffuse patch of nebulosity to
its immediate south. Much easier to see than without a filter.
UHC: (4) Almost fan-like diffuse patch extending from the faint star to its
south. More nebulosity visible than in Deep-Sky, but still somewhat small.
OIII: (4) Fainter than UHC, but the nebula now envelopes the star in a
diffuse faint haze. Darker inclusion from the northeast now visible.
H-beta: (1) Really dims it!
RECOMMENDATION FOR Sh-2-112: OIII/UHC (H-beta not recommended).

Sh2-132 (Diffuse Nebula in Cepheus)
DEEP-SKY: (2) better than without filters as without filters the object is
only hinted at. Just a very faint diffuse irregular glow around several stars
roughly elongated east-west.
UHC: (4) Makes a patch on south edge easier to see and hints of other detail.
OIII: (4) Increases contrast with an arc across the northern side and a patch
in the middle. Higher contrast but dimmer than UHC.
H-BETA: (2) Dims it more than OIII, but nebula remains visible.

Sh2-142 (Diffuse Nebula in Cepheus around open cluster NGC 7380)
DEEP-SKY: (2) hint of a glow across fairly rich star cluster.
UHC: (4) big fat triangular area, faint arc-like appendages.
OIII: (4) fainter, but more dark detail, with "Y" shape to the nebula..
H-Beta: (3) fainter than OIII, but still visible (better than Deep-Sky).

Sh2-155 (Diffuse nebula in Cepheus).
DEEP-SKY: (2) very faint diffuse area of haze around two widely-spaced stars
(better contrast than without a filter).
UHC: (1) Only hint of nebulosity visible.
OIII: (1) little if any nebulosity visible.
H-BETA: (0) no nebulosity visible.
RECOMMENDATION FOR Sh-2-155: DEEP-SKY (probable reflection nebula).

Sh2-157 ("fingers" diffuse nebula in Cassiopeia).
DEEP-SKY: (2) not easily seen except as a vague elongated brightening in a
rich star background.
UHC: (3) Elongated large diffuse and dim oval feature with two dim northward-
pointing arcs.
OIII: (3) Nebula is fainter than in UHC, but still visible with increased
contrast, especially in the two "finger" patches.
H-BETA: (2) Fainter than in OIII, but nebula is still visible.

Sh2-170 (faint diffuse nebula in Cepheus).
DEEP-SKY: (2) not easy to see without filters. Round very faint very diffuse
patch of haze around a group of 6 or 7 faint stars.
UHC: (3) Somewhat easier to see than in Deep-Sky, with a bit more contrast.
OIII: (2) Still visible, but fainter than in UHC.
H-BETA: (2) Still visible but fainter than in OIII or UHC.

Sh2-171 (very faint large diffuse nebula in Cepheus).
DEEP-SKY: (2) Plainly visible over non-filter, but still faint and diffuse.
UHC: (3) Slight enhancement over Deep-Sky with some light and dark areas.
OIII: (2) Fainter but shows more enhancement in several dark lane-like
H-BETA: (2) Nebula remains visible, but just a bit fainter than in the OIII.
RECOMMENDATION FOR Sh-2-171: UHC (Deep-Sky and OIII filters also useful).

Sh2-235 (diffuse nebula in Auriga).
DEEP-SKY: (3) diffuse oval faint fuzzy patch, slight southern extension.
UHC: (3): slightly more contrast than Deep-Sky, but fainter.
OIII: (2): fainter than UHC or Deep-Sky.
H-BETA: (4): Faint, but two patches are now seen with brighter one on the
north. More contrast than Deep-Sky or UHC.

Sh2-261 (diffuse nebula in Orion):
DEEP-SKY: (2) slight increase in contrast making the nebula faintly visible
and easier than without a filter.
UHC: (3) nebula now clearly visible but still faint.
OIII: (3) nebula visible, but fainter than UHC with a bit more contrast.
H-BETA: (2), nebula is still visible, but not quite as good as in UHC/OIII.

Sh2-276 "BARNARD'S LOOP" (diffuse nebula in Orion).
**(Naked-eye observations with filter over unaided eye).
DEEP-SKY: (1) hint of a glow in telescope, but not visible naked eye.
UHC: (2) Faint arc like glow visible under good conditions over Orion's Belt,
continuing southward east of the belt.
OIII: (0) No nebulosity seen.
H-BETA: (3) Faint glow visible both over the belt and curving down southeast
along Orion's southeastern side. Very faint, but noticably easier to see
than in UHC filter.
RECOMMENDATION FOR Sh2-276: H-BETA/UHC. (OIII not recommended)

Sh2-254-5-6-7-8 (dim nebular complex in northern Orion: IC 2162).
DEEP-SKY: (2) three dim diffuse patches in a line.
UHC: (3): Increased contrast (Sh2-257 now brightest of the three large ones).
OIII: (2): fainter than in UHC and Sh2-255 now not as large.
H-BETA: (3): more contrast than UHC but a bit dimmer.
RECOMMENDATIONS FOR Sh2-254 complex: H-BETA/UHC (near tie).

vdB93 (Gum-1) (diffuse nebula in Monoceros near IC 2177).
DEEP-SKY: (2) Slight boost in contrast, showing more nebulosity than without
a filter.
UHC: (3) More contrast and nebulosity visible, but still faint.
OIII: (1) Fainter than in UHC, with only hint of a glow around the central
H-BETA: (4) Better defined than any of the other filters, with more light and
dark detail. Fainter than in UHC, but shows better contrast and detail.
RECOMMENDATION FOR vdB93: H-BETA/UHC (OIII not recommended).


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