The Urban Imager’s Cheat Sheet

Filter selection, camera settings, and moon planning for 25 deep-sky objects

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This reference table is the practical companion to the Bortle-9 Imaging Index. It covers all 25 targets in the study with recommended filters, camera settings, and moon planning guidance—everything you need to make decisions in the field without second-guessing.

The settings here are starting points based on my equipment (Askar FRA300 Pro, ZWO ASI585MC, ASIAIR) and location (Bortle 9, Chicago suburbs). Your mileage may vary, but the principles should translate: dual-band filters for emission targets, broadband for galaxies, and respect the moon when shooting broadband.

How to use this table:

• Check the season to see what's well-positioned now

• Match filter to target type—SV220 for emission, L-QEF for broadband

• Note the moon tolerance before planning your session

• Start with the suggested gain and histogram peak, then adjust based on your conditions

• Stick to the sub length guidance to balance signal and light pollution

The tier ratings reflect my predictions for what's achievable in a one-hour session from Bortle 9. As I collect real data through the Index project, these may shift—that's the point.

Bortle-9 Index: Target Filter & Settings Reference — 1 Hour Workflow (30–60s Subs)

Target	Tier	Best Filter	Why This Filter Works	Gain (ASI585MC)	Histogram Peak (%)	Sub Length	Moon Tolerance	Notes
WINTER (Dec–Feb)
M42 — Orion Nebula	5 - Easy	L-QEF	Mixed emission + reflection; quad-band preserves natural color and core structure	200	20–25%	30–45s	Moderate	Short subs prevent core blowout
M45 — Pleiades	5 - Easy	L-QEF	Reflection nebulosity requires broadband; field-tested from Bortle 9	200	20–25%	30–45s	Low	Reflection nebulae are moon-sensitive
M1 — Crab Nebula	3 - Moderate	SV220 or L-QEF	Mixed emission SNR; try both and compare	250	25–30%	45–60s	Moderate	Small target; benefits from good seeing
NGC 2244 — Rosette	3 - Moderate	SV220	Strong Ha response; dual-band enhances rim and inner cavity	250	25–30%	45–60s	High	One of the best winter dual-band targets
IC 434 — Horsehead	2 - Tough	SV220	Dual-band Ha/OIII isolation boosts contrast in faint IC 434 curtain	250	25–30%	45–60s	High	Dual-band helps; still a tough target
NGC 2359 — Thor's Helmet	2 - Tough	SV220	OIII-dominant bubble nebula; dual-band essential	250	25–30%	60s	High	Faint; needs good transparency
Barnard's Loop	1 - Unlikely	SV220	Ha-only emission; extremely faint and huge	300	30–35%	60s	High	Probably needs dark skies or many hours
Sh2-240 — Spaghetti Nebula	1 - Unlikely	SV220	Ha-dominant SNR; notoriously faint	300	30–35%	60s	High	20+ hours needed from dark sites
SPRING (Mar–May)
M81 — Bode's Galaxy	3 - Moderate	L-QEF	Broadband preserves spiral structure, dust lanes, and natural color	200	20–25%	45s	Low	Excellent framing with M82
M82 — Cigar Galaxy	2 - Tough	L-QEF	Broadband captures starburst core; L-QEF enhances Ha outflows	200	20–25%	45s	Low	Pairs perfectly with M81 in one frame
M51 — Whirlpool Galaxy	3 - Moderate	L-QEF	Broadband needed for spiral arms and companion interaction	200	20–25%	45s	Low	Needs good transparency
M101 — Pinwheel Galaxy	3 - Moderate	L-QEF	Preserves faint outer arms; low surface brightness challenge	200	20–25%	45s	Low	Best near zenith to fight gradients
M97 — Owl Nebula	2 - Tough	SV220	OIII-dominant planetary nebula; dual-band essential	250	25–30%	60s	High	Small, faint; near M108 for nice pairing
IC 1101	1 - Unlikely	L-QEF	Distant giant elliptical; broadband only option	200	20–25%	45–60s	Low	Too faint and small for 1 hour
SUMMER (Jun–Aug)
M8 — Lagoon Nebula	5 - Easy	SV220	Ha-dominant emission; dual-band punches through LP	250	25–30%	45–60s	High	Low altitude from Chicago (~25° max)
M17 — Omega Nebula	4 - Should Work	SV220	Bright Ha/OIII emission; compact and contrasty	250	25–30%	45–60s	High	Great summer dual-band target
M27 — Dumbbell Nebula	4 - Should Work	SV220	Strong OIII response; high surface brightness	250	25–30%	45–60s	High	Forgiving target; great for beginners
NGC 6992 — Eastern Veil	4 - Should Work	SV220	OIII-dominant SNR; dual-band magic	250	25–30%	60s	High	Excellent from Chicago; part of larger complex
NGC 7000 — North America	5 - Easy	SV220	Ha-dominant emission; large and bright	250	25–30%	45–60s	High	Circumpolar but best when high
FALL (Sep–Nov)
M31 — Andromeda Galaxy	5 - Easy	L-QEF	Broadband preserves natural color; bright core anchors processing	200	20–25%	30–45s	Low	High overhead; long imaging window
M33 — Triangulum Galaxy	4 - Should Work	L-QEF	Broadband needed; L-QEF enhances HII regions in arms	200	20–25%	45–60s	Low	Low surface brightness; needs patience
M74 — Phantom Galaxy	2 - Tough	L-QEF	Broadband only; notoriously low surface brightness	200	20–25%	60s	Low	Very challenging from Bortle 9
IC 1396 — Elephant Trunk	4 - Should Work	SV220	Ha/OIII emission complex; huge and detailed	250	25–30%	60s	High	Excellent dual-band target
Cassiopeia A	1 - Unlikely	SV220	Faint optical SNR; radio-bright but dim visually	300	30–35%	60s	High	Extremely faint in optical; good luck!
Abell 85 — CTB 1	1 - Unlikely	SV220	OIII-dominant SNR; ultra-faint	300	30–35%	60s	High	Would need many hours from dark site

Moon Tolerance Key

Rating	Meaning
High	Dual-band filter blocks most moonlight; image within 30° of moon if needed
Moderate	Some moon tolerance; keep moon >50° away
Low	Broadband target; avoid moon entirely or wait for new moon phase

Summary by Filter

Filter	Targets	Use Case
SV220 (dual-band)	14	Emission nebulae, planetary nebulae, SNRs
L-QEF (quad-band)	10	Galaxies, reflection nebulae, clusters
Either	1	Mixed emission—experiment with both

For optimal imaging windows and transit times, download the 2026 Planning Calendar.

Want to understand why these gain values? See Understanding ASI585MC Gain Settings

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Clear skies,
Pete