Filter Performance Comparisons for Some Common Nebulae by David Knisely (KA0CZC@navix.net) Prairie Astronomy Club see web page for details on this data (hyperlink to right).                                          
Object Common Name (Description) Final Recommendation Deepsky UHC OIII H-beta                                          
M1  CRAB NEBULA (SNR in Taurus) M1: UHC/DEEP-SKY (H-beta not recommended). 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.  
M8 LAGOON NEBULA (diffuse Nebula in Sagittarius). M8: UHC/OIII 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 b 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) M16: UHC/OIII, but H-BETA hurts the view. 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 visible.  
M17 SWAN (OMEGA) NEBULA (diffuse nebula in Sagittarius) M17: OIII/UHC (H-BETA not recommended). 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 shape. 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 notica 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) M20: UHC/H-BETA. 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 views. 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) RECOMMENDATIONS FOR M27: UHC (OIII also useful in showing some inner detail, but H-BETA is NOT recommended). 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.  
M42 GREAT ORION NEBULA (diffuse nebula) M42: UHC/OIII (near-tie)*** 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 i 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 als  
M43 (north part of Great Orion Nebula). M43: H-BETA (UHC and Deep-Sky also help). 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.  
M57 RING NEBULA (planetary nebula in Lyra) 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!) 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 much. 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.  
M76 MINI-DUMBELL or BUTTERFLY NEBULA (planetary nebula in Perseus): M76: OIII/UHC (H-BETA NOT recommended!). 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): M97: OIII/UHC (H-beta not recommended). 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.  
NGC 40 (Planetary Nebula in Cepheus): NGC 40: DEEP-SKY/UHC (near tie). 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): NGC 246: OIII. (H-Beta not recommended). 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).  
NGC 281 (Diffuse emission nebula (Cassiopeia): NGC 281: UHC/OIII. 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). NGC 604: OIII/UHC. 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). NGC 896/IC 1795: UHC/OIII (H-beta not recommended). 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.  
NGC 1360 (large Planetary Nebula in Fornax). NGC 1360: OIII/UHC (H-beta not recommended). 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.  
NGC 1499 CALIFORNIA NEBULA (diffuse Nebula in Perseus). Without filters, the nebula is barely visible as a faint brightening of the field with no detail. CALIFORNIA NEBULA: H-BETA. 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): NGC 1514: OIII/UHC (H-Beta NOT recommended). 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): NGC 1999: DEEP-SKY 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): NGC 2022: OIII/UHC (H-Beta NOT recommended). 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) NGC 2024: DEEP-SKY/UHC (near tie). DEEP-SKY: (3) Noticably improves the contrast with the dark lane-like detail visible. 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). NGC 2174: UHC/OIII (near tie) (H-Beta NOT recommended). 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-Sky.  
NGC 2327 (diffuse nebula in Monoceros). NGC 2327: H-BETA/UHC 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). ROSETTE NEBULA: OIII/UHC (near tie). 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. CONE NEBULA: UHC. 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): NGC 2346: UHC/OIII (near tie) (H-beta not recommended). 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.  
NGC 2438 (planetary nebula in Puppis). NGC 2438: OIII (H-Beta not recommended). DEEP-SKY (2) noticably easier to see than without a filter. Hints of annularity. 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.  
NGC 2467 THOR'S HELMET (diffuse nebula in Puppis). NGC 2467: OIII/UHC (H-Beta not recommended). 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 arc 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.  
NGC 2359 (diffuse nebula in Canis Major). NGC 2359: OIII/UHC (H-Beta not recommended). 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 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.  
NGC 2371-2 (planetary nebula in Gemini). NGC 2371-2: OIII/UHC (near tie) (H-Beta not recommended) 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.  
NGC 2392 ESKIMO NEBULA (planetary nebula in Gemini) NGC 2392: OIII/UHC. (H-Beta not recommended). 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.  
NGC 3242 GHOST OF JUPITER (planetary in Hydra). NGC 3242: UHC/OIII (near tie) (H-Beta not recommended). 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).  
NGC 4361 (planetary nebula in Corvus): NGC 4361: UHC/OIII (near tie), (H-Beta not recommended). 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.  
NGC 6210 (planetary nebula in Hercules). NGC 6210: OIII/UHC (H-Beta not recommended). 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.  
NGC 6302 BUG NEBULA (planetary nebula in Scorpius). NGC 6302: OIII/UHC (H-Beta not recommended). 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).  
NGC 6334 (diffuse nebula in Scorpius). NGC 6334: UHC (OIII and H-beta also useful). 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.  
NGC 6445 (Planetary Nebula in Sagittarius). NGC 6445: UHC/OIII (H-beta not recommended). 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.  
NGC 6357 (diffuse nebula in Scorpius). NGC 6537: OIII/UHC (H-Beta not recommended). 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.  
NGC 6543 CAT'S EYE (planetary nebula in Draco). NGC 6543: OIII/UHC (H-Beta not recommended). 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.  
NGC 6559/IC 4685 (diffuse nebula in Sagittarius). NGC 6559: UHC 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). NGC 6781: OIII/UHC (H-beta not recommended). 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.  
NGC 6804 (Planetary nebula in Aquila). NGC 6804: OIII/UHC (H-beta not recommended). 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.  
NGC 6888 CRESCENT NEBULA (diffuse nebula in Cygnus). NGC 6888: OIII/UHC (near tie). H-beta not recommended!) 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.  
NGC 6960-95 VEIL NEBULA (SNR in Cygnus). VEIL: OIII (UHC is helpful, but not quite as much as the OIII. H-BETA is NOT recommended). DEEP-SKY: (3) Nebula is easier to see than without a filter, with both sides ofthe 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. OIII: (5) ENORMOUS INCREASE IN CONTRAST AND DETAIL with wonderful fine filaments and strands visible even between the two main arcs, making the entire complex closely resemble its photograph. OIII is the filter of choice here. H-BETA: (1) Very dim, but still visible (forget it!).  
NGC 7000 NORTH AMERICAN NEBULA (diffuse nebula in Cygnus). NGC 7000: UHC/OIII but both H-BETA/Deep-Sky are useful on the object (UHC was brighter, but OIII shows more contrast). 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.  
NGC 7009 SATURN NEBULA (planetary nebula in Aquarius). NGC 7009: Filters are not needed, but OIII/UHC will help bring out the fainter detail (H-BETA not recommended). 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.  
NGC 7023 Emission/reflection Nebula in Cepheus. NGC 7023: DEEP-SKY. 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 7027 (Planetary nebula in Cygnus). NGC 7027: OIII/UHC near tie (H-BETA not recommended!). 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!  
NGC 7129-33 (Diffuse Nebula in Cepheus) NGC 7129-33: UHC/OIII 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 7293 GIANT HELICAL NEBULA (planetary nebula in Aquarius). NGC 7293: OIII/UHC (H-beta NOT recommended). 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 contrast. 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).  
NGC 7538 (Diffuse nebula in Cepheus): NGC 7538: UHC/OIII (H-beta NOT recommended). DEEP-SKY: (3) boosts the contrast making it easier to see than without a filter. UHC: (4) darkens the background and brings out the nebulosity more than Deep-Sky. OIII: (4) dimmer, but contrast is a bit higher. H-BETA: (0) Dims it nearly to extinction.  
NGC 7635 BUBBLE NEBULA (diffuse nebula in Cassiopeia). NGC 7635: OIII/UHC. 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). NGC 7662: Filters are not really needed, but UHC/OIII may help with locating it at low power via "blinking" (H-BETA is not recommended). 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.  
NGC 7822 (faint diffuse nebula in Cepheus). NGC 7822: UHC (H-Beta and OIII also useful). 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.  
IC 405 FLAMING STAR NEBULA (diffuse emission/reflection nebula in Auriga). IC 405: DEEP-SKY/UHC (no filter helps a lot, and may be mostly a reflection nebula). 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.  
IC 410 (Nebula assoc. with NGC 1893 in Auriga) IC 410: OIII/UHC. (H-beta not recommended). 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 cluster. H-BETA: (0) Nebula is almost wiped out.  
IC 434 HORSEHEAD NEBULA (diffuse nebula in Orion). HORSEHEAD: Lumicon H-BETA (UHC also helps, but OIII not recommended). 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 only hinted at. 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). IC 1318. H-BETA/UHC (near tie) (OIII not recommended) 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.  
IC 1396 (nebula S.W. of Mu Cephei). IC 1396: UHC/DEEP-SKY. (OIII not recommended). 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: (0) Kills the nebulosity. H-BETA: (1) Nebulosity is visible, but is extremely dim in a dark background.  
IC 1848 (Diffuse Nebula, Cassiopeia). IC 1848: UHC (H-beta not recommended) 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.  
IC 2177 (Diffuse Nebula, Monoceros). IC 2177: H-BETA/UHC. 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 degrees. 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): IC 4628: UHC. 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.  
PELICAN NEBULA (IC 5067-70) (diffuse nebula in Cygnus): IC 5067: UHC/OIII, Deep-sky also useful on the object (UHC was brighter, but OIII shows more detail). 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.  
IC 5146 THE COCCOON NEBULA (diffuse nebula in Cygnus). IC 5146: H-BETA/UHC near tie (OIII not recommended). 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 features.  
PK205+14.1 MEDUSA NEBULA (large planetary nebula in Gemini): PK204+14.1: OIII/UHC near tie (H-beta not recommended). 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.  
PK164+31.1 HEADPHONE NEBULA (large planetary nebula in Lynx). PK164+31.1: UHC/OIII near tie (H-beta not recommended). 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.  
Sh-2-13 (Diffuse nebula in Scorpius). SH-2-13: UHC 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.  
Sh-2-54 (Diffuse nebula in Serpens). Sh-2-54: UHC 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.  
Sh-2-84 (Diffuse nebula in Sagitta). Sh-2-85: UHC. 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.  
Sh-2-101 (Diffuse Nebula in Cygnus): Only hinted at without filters. Sh-2-101: UHC/H-BETA. 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.  
Sh-2-112 (Diffuse Nebula in Cygnus N.W. of Deneb): hinted at without filters. Sh-2-112: OIII/UHC (H-beta not recommended). 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!  
Sh-2-132 (Diffuse Nebula in Cepheus) Sh-2-132: OIII/UHC. 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: (3) 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.  
Sh-2-155 (Diffuse nebula in Cepheus). Sh-2-155: DEEP-SKY (probable reflection nebula). 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.  
Sh-2-157 ("fingers" diffuse nebula in Cassiopeia). Sh-2-157: UHC/OIII 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.  
Sh-2-170 (faint diffuse nebula in Cepheus). Sh-2-170: UHC 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.  
Sh-2-171 (very faint large diffuse nebula in Cepheus). Sh-2-171: UHC (Deep-Sky and OIII filters also useful). 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 structures. H-BETA: (2) Nebula remains visible, but just a bit fainter than in the OIII.  
Sh-2-261 (diffuse nebula in Orion): Sh-2-261: UHC/OIII (near tie). 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.  
Sh-2-276 BARNARD'S LOOP (diffuse nebula in Orion).**(Naked-eye observations with filter over unaided eye). Sh-2-276: H-BETA/UHC. (OIII not recommended)> 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.  
Sh-2-235 (diffuse nebula in Auriga). Sh-2-235: H-BETA/DEEP-SKY (UHC also helps.). 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.  
vdB93 (Gum-1) (diffuse nebula in Monoceros near IC 2177). vdB93: H-BETA/UHC (OIII not recommended). 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 star. 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.