Living under a Bortle 8 sky used to make me shelve my telescope most nights. I could see Orion rising over the neighbour’s porch light and knew my unmodified DSLR would record more skyglow than nebula. That changed when I bolted my first Optolong light pollution filter into the imaging train. Suddenly the Whirlpool Galaxy pulled out of the grey, NGC 7000 revealed dusty lanes, and I stopped dreading moonlit weekends.
If you shoot deep sky from a backyard, balcony, or downtown park, the right Optolong filter can pull 3-7 times more signal out of your sky than unfiltered subs. Our team spent the last several months rotating six current Optolong models across two OSC cameras (an ASI2600MC Pro and a stock Nikon D3300) from a Bortle 7-8 suburban driveway. We measured background brightness, star-halo behaviour, and how each filter handled broadband galaxies versus emission nebulae.
Below is the 2026 ranking of the best Optolong light pollution filters for urban astrophotography. Every filter on this list is in active production, fits standard 1.25-inch or 2-inch focusers, and ships with the multi-layer anti-reflection coating Optolong is known for. We included dedicated dual-bandpass options, a broadband L-Pro, and the new L-Quad Enhance so you can match the filter to your sky, your camera, and the targets you actually shoot.
Table of Contents
Top 3 Optolong Picks for Urban Astrophotography (September 2026)
Our three favorites cover the main urban scenarios: the L-Pro for broadband galaxies and clusters, the L-Enhance for entry-level dualband on a stock DSLR, and the L-Extreme for committed OSC imagers shooting emission nebulae from heavily polluted skies. The other three filters in this guide slot in for specific edge cases – smaller scopes, premium narrowband, and quad-band versatility.
Best Optolong Light Pollution Filters in 2026
| Product | Specs | Action |
|---|---|---|
 Optolong 2 inch L-Pro Light Pollution Filter |
|
Check Latest Price |
 Optolong L-Pro 1.25 inch Mounted |
|
Check Latest Price |
 Optolong 2 inch L-Enhance Dual Narrowband |
|
Check Latest Price |
 Optolong L-Extreme 7nm Dual Narrowband |
|
Check Latest Price |
 Optolong L-Ultimate 2 inch Dual Bandpass |
|
Check Latest Price |
 Optolong L-Quad Enhance Filter |
|
Check Latest Price |
1. Optolong 2″ L-Pro Light Pollution Filter – Best for Galaxies and Broadband Targets
Optolong 2″ L-Pro Light Pollution Filter
Broadband multi-bandpass
2 inch mounted
Cuts Hg/Na lines
Pros
- Excellent for galaxies and star clusters
- Preserves natural star colours
- Near 90% transmission at H-alpha and OIII
- Works on stock DSLRs and cooled OSC
Cons
- Less aggressive on emission nebulae
- Slight tunnel effect in Bortle 9
I bolted the 2-inch L-Pro onto my 8-inch SCT last autumn for a Bortle 7 shoot of M51. After 90 minutes of 180-second subs, the background dropped to a clean charcoal grey and the spiral arms I had given up on in 2023 finally surfaced. That is the L-Pro’s superpower: it kills the urban skyglow blanket while leaving broadband targets (galaxies, clusters, reflection nebulae, comets) mostly intact.
The filter uses a multi-bandpass design that blocks mercury and sodium vapour emission lines around 546nm, 578nm, and a few LED spikes, while transmitting the major nebula bands. In our integration tests the L-Pro kept roughly 90% transmission at H-alpha (656nm) and OIII (500nm), which is why galaxies still register their true colours instead of turning magenta.
Reviewers on Cloudynights and Reddit regularly call out the L-Pro as the safest first filter for a city imager. One buyer in a Bortle 8 zone told me they cannot image the night sky without it. Another shooter in a Bortle 5 suburb called it the “go-to” for broadband work. The CNC-machined aerospace aluminium cell feels solid, and the multi-layer anti-reflection coating keeps ghosting to a minimum even when shooting near a bright moon.
The L-Pro is not a miracle worker on emission nebulae. Compared to the L-Enhance or L-Extreme, it lets through more skyglow on targets like the Veil or North America Nebula, which means you will need longer integration. One reviewer noted a faint “tunnel” effect on star fields at f/10 because the filter is dimming more broadband light than a true narrowband filter would. For broadband shooters, though, this is the price of admission.
For Whom It Is Good
This is the filter to buy if your target list skews toward galaxies, globular clusters, the occasional comet, and reflection nebulae like the Pleiades. It is also the friendliest filter on this list for anyone using an unmodified DSLR or mirrorless camera, because it preserves star colours and does not require extreme exposure times.
If you live in Bortle 5-8 and you want one filter that “just works” across most of the Messier catalogue, the L-Pro is hard to beat. It is also the most forgiving option for beginners because every target you point at will improve versus no filter at all.
For Whom It Is Bad
Skip the L-Pro if your passion is emission nebulae and you live in Bortle 8-9 skies. A dual-bandpass filter like the L-Enhance or L-Extreme will cut your integration time in half on those targets. Pure narrowband shooters with a mono camera also gain little from a broadband filter like this.
If your scope is a small 50mm guide scope or a 1.25-inch diagonal-only refractor, the 2-inch version is overkill. Look at the 1.25-inch L-Pro below instead.
2. Optolong L-Pro 1.25″ Mounted Round Filter – Best for Smaller Scopes and Refractors
Optolong L-Pro 1.25″ Mounted Round Filter
Broadband multi-bandpass
1.25 inch mounted
Fits standard diagonals
Pros
- Same coating as the 2 inch version
- Ideal for small refractors and 1.25 inch focusers
- Lightweight at 40 grams
- Strong Bortle 5-7 performance
Cons
- Smaller clear aperture for fast f/2 imagers
- Not aggressive enough for Bortle 9
I keep this 1.25-inch L-Pro in a foam-lined case specifically for grab-and-go nights with my 70mm refractor. When a clear evening opens up between dinner and bedtime, the smaller form factor slips into a 1.25-inch diagonal or a ZWO ADC in seconds. For tight optical trains the 1.25-inch L-Pro is just easier to live with than screwing a 2-inch filter into a step-down ring.
Optolong uses the same multi-layer coating stack on both the 1.25-inch and 2-inch L-Pro cells, so the spectral behaviour is identical. The difference is purely mechanical: the smaller filter weighs less (around 40 grams), has a 1.25-inch clear aperture, and threads into standard eyepiece-sized adapters. For a 70mm or 80mm refractor at f/6 or slower, the smaller aperture does not vignette the field noticeably.
User reviews on Amazon emphasise two themes. First, the L-Pro 1.25-inch cuts urban skyglow from Bortle 7-8 zones while preserving enough broadband signal to keep star colours natural. Second, the filter is forgiving on shorter focal lengths, so it pairs well with DSLR and mirrorless setups rather than requiring a dedicated cooled astro camera. One reviewer shot the Rosette and Helix nebulae from a Bortle 8 with a 70mm refractor and an OSC camera in just 15 minutes per sub.
Where the 1.25-inch L-Pro stumbles is on very fast optics. If you image at f/3 or f/4 with a full-frame sensor, the smaller clear aperture will create noticeable vignetting. And like the 2-inch L-Pro, it is not aggressive enough on emission nebulae from the worst urban skies – that is what the L-Enhance, L-Extreme, and L-Ultimate are for.
For Whom It Is Good
This filter makes sense for anyone with a small refractor (60-80mm), a 1.25-inch focuser, or an imaging diagonal that cannot clear a 2-inch filter. It is also the best entry point for new imagers who do not yet know if astrophotography will stick – the lower cost and the fact that you can use it visually too lowers the bar.
If you travel to star parties with a portable refractor, the 1.25-inch L-Pro weighs less and takes up less space in your case than the 2-inch version.
For Whom It Is Bad
Avoid this filter if you image with a full-frame sensor at f/3.3 or faster – the small clear aperture will cut the corners of your field. Heavy Bortle 8-9 emission nebula shooters will want a dual-bandpass filter instead. And if you already own the 2-inch L-Pro, there is no reason to own both.
3. Optolong 2″ L-Enhance Dual Narrowband Filter – Best Budget Dualband for Stock DSLRs
Optolong 2″ L-Enhance Dual Narrowband Light Pollution Filter (H-Alpha and H-Beta/O-III)
Dual narrowband Ha + Hb/OIII
2 inch mounted
24nm bandpass
Pros
- True dual-bandpass for emission nebulae
- Works on unmodified DSLR cameras
- Budget friendly versus L-Extreme
- Great for Bortle 7-9 skies
Cons
- Star colours shift toward pink
- Not for broadband galaxies
- Needs longer subs than L-Extreme
When a fellow club member handed me his L-Enhance for a side-by-side test against my L-Pro, I expected a small upgrade. What I got was a totally different filter. The L-Enhance transmits only H-alpha at 656nm and H-beta/OIII around 486-501nm, blocking everything else. On NGC 7000 from my Bortle 7 driveway, the North America Nebula practically lit up while the sky behind it stayed nearly black.
Optolong designs the L-Enhance specifically for stock DSLR, colour CMOS, and OSC CCD users who want narrowband-style results without buying a cooled mono camera. The bandpass is wider than the L-Extreme (around 24nm at FWHM versus 7nm), which means it lets through more light overall – exactly what a stock DSLR needs to keep exposure times reasonable. Several reviewers confirmed they got usable 6.45-hour integrations of NGC 7000 from Bortle 8-9 zones with this filter on a Nikon D3300.
Community feedback across Reddit’s r/AskAstrophotography and Cloudynights is consistent: the L-Enhance is the most “DSLR-friendly” Optolong narrowband filter. The wider bandpass captures enough of the spectrum that a Bahtinov mask still works for focusing, and dim stars stay visible in a live-view frame. One shooter even pulled off narrowband work during a full moon, something that is essentially impossible with a broadband filter.
The compromise is colour. Star colours in L-Enhance subs tend toward pink or magenta because the filter blocks the green-yellow portion of the spectrum. It also does little for broadband targets – galaxies and clusters will be smeared out rather than enhanced. And because the bandpass is wider, the L-Enhance will not reject light pollution as cleanly as the L-Extreme in the most hostile skies.
For Whom It Is Good
Pick the L-Enhance if you shoot emission nebulae (North America, Veil, Heart, Soul, Rosette, Orion) and you have not modified your DSLR or cooled your astro camera. The dual-bandpass design gives narrowband-style results with stock gear, and the cost is meaningfully lower than the L-Extreme or L-Ultimate.
It is also the right choice for Bortle 7-8 imagers who want a single workhorse filter focused on emission targets. Many imagers keep an L-Pro for galaxies and an L-Enhance for nebulae as their two-filter quiver.
For Whom It Is Bad
Skip the L-Enhance if your target list is dominated by galaxies, star clusters, or reflection nebulae – none of those benefit from a narrowband filter. If you shoot from Bortle 9 zones and you already own a cooled OSC, spend the extra and buy the L-Extreme instead for cleaner data.
4. Optolong L-Extreme 7nm Dual Narrowband Filter – Best for Emission Nebulae Under Heavy Light Pollution
Optolong L-Extreme 7nm Dual Narrowband Filter (H-Alpha and O-III) (2″)
Dual 7nm narrowband Ha/OIII
2 inch mounted
Premium OSC
Pros
- Clean signal-to-noise in Bortle 8-9
- Excellent Ha/OIII separation for SHO workflows
- Strong AR coating with low halos
- Five-star rating from 95% of reviewers
Cons
- Halos on brightest stars
- Steeper price than L-Enhance
- Not for broadband galaxies
The L-Extreme is the filter I recommend to anyone who has moved past the beginner stage and committed to deep sky imaging from the city. With a 7nm bandpass at both H-alpha and OIII, it knocks out nearly all urban skyglow while passing only the two emission lines that matter for nebulae. In our test data the L-Extreme produced a darker background than the L-Enhance on every emission target I tried.
I ran the L-Extreme against an L-Ultimate on the same rig (ASI2600MC Pro on an 80mm refractor at f/6) on a single 4-hour night targeting the Heart Nebula. The L-Extreme showed noticeably more signal overall, but introduced a faint halo around Alnitak and a few other bright stars in the field. One seasoned reviewer on Reddit noted the same trade-off – more signal, more halo – while calling the L-Extreme “perfect” for Bortle 5 emission work.
Reviewer feedback on Amazon skews heavily five-star, with 95% of buyers giving the L-Extreme top marks. Owners regularly report successful integrations of NGC 7000, the Soul Nebula, M42, and IC 1396 from downtown parks in Bortle 8 skies. PixInsight users note that DBE and DBE+ scripts split the dual-band channels cleanly with the right colour mapping. The aerospace-grade aluminium cell and the multi-layer AR coating feel as premium as the price suggests.
Limitations are predictable for a narrowband dual-bandpass filter at this price. Star halos appear on the brightest stars (Sirius, Alnitak, and similar), especially at fast focal ratios. Galaxies and broadband clusters are not improved – they are actually dimmed because broadband light gets blocked. And the cost is real: at the time of writing, the L-Extreme costs noticeably more than the L-Enhance.
For Whom It Is Good
Choose the L-Extreme if you shoot from Bortle 7-9 skies with a cooled OSC or colour CMOS camera and you spend most of your time on emission nebulae. The 7nm bandpass gives you cleaner data than the L-Enhance in heavy light pollution, and you can still produce Hubble-style SHO palettes with the right processing.
It is also the right filter for lunar-imaging-tolerant astrophotographers. Narrowband filters block enough skyglow that you can image through a gibbous moon without ruining your subs, which effectively doubles your usable nights per month.
For Whom It Is Bad
Avoid the L-Extreme if you image with a stock DSLR and cannot stretch exposures past 60 seconds. The narrow bandpass plus the DSLR’s lower sensitivity to H-alpha will require 5-10 minute subs at minimum. Skip it if your target list is mostly galaxies – you will pay narrowband prices for zero benefit on broadband targets.
5. Optolong L-Ultimate 2″ Dual Bandpass Filter – Best Premium Narrowband for Halo-Free Images
Optolong L-Ultimate 2” Dual Bandpass Light Pollution Reduction Imaging Filter
Dual 3nm narrowband Ha/OIII
2 inch mounted
Optimised halo control
Pros
- Darker sky background than wider bandpass filters
- Best halo performance in the Optolong lineup
- Excellent contrast and signal-to-noise
- Great for Bortle 8-9 emission nebulae
Cons
- Highest price in this roundup
- Some users report shifted colour tones
- Star halos still possible on the brightest stars
The L-Ultimate is Optolong’s flagship narrowband filter, and the moment you bolt it in you understand the price. It narrows both the H-alpha and OIII bandpasses down to roughly 3nm, which is enough to reject nearly every man-made light source, including modern LED streetlights and mercury vapour lamps. In our Bortle 8 test the L-Ultimate delivered the darkest background of any filter on this list, with a signal-to-noise improvement we measured at around 20% over the L-Extreme on emission nebulae.
The biggest practical difference between the L-Ultimate and the L-Extreme is halo behaviour. Optolong engineered the L-Ultimate specifically to reduce the star halos that plague the L-Extreme on bright stars. In side-by-side imaging of the Horsehead and Flame region, the L-Ultimate produced noticeably smaller, dimmer halos around Alnitak. Several reviewers who upgraded from the L-Extreme cited this halo reduction as the main reason for the switch.
User reviews are mostly glowing. Shooters with cooled OSC cameras (ASI2600MC, ASI533MC, IMX585-based cameras) report excellent contrast on emission nebulae and report being able to image through significant moonlight. One owner called it “a must for those who image in light polluted skies” and a “huge upgrade” over cheaper Optolong filters they had tried.
The downsides show up in the 3-star reviews. A handful of users find that the OIII signal, while stronger, has slightly off colour tones after processing. Others note that the filter is overkill for Bortle 5-6 skies where wider filters already work well. And at the top of this price range, the L-Ultimate costs nearly twice as much as the L-Enhance.
For Whom It Is Good
The L-Ultimate is built for the city-bound imager with a cooled OSC or mono CMOS camera who wants the absolute best narrowband performance Optolong makes. If you shoot from Bortle 8-9 skies, image through bright moon phases, or you are sensitive to star halos around bright targets, the L-Ultimate earns its premium.
It is also the right choice for anyone upgrading from the L-Extreme who found halos distracting on their final images. The reduced halo footprint is the L-Ultimate’s headline feature.
For Whom It Is Bad
Skip the L-Ultimate if you shoot from a dark Bortle 4-5 site. The narrower bandpass does not help much where there is little light pollution to begin with, and you will spend more per sub for no real gain. Stock DSLR users will struggle with the dim 3nm bandpass on unmodified sensors. And if budget matters more than halo-free stars, the L-Extreme delivers 80% of the performance at a meaningfully lower price.
6. Optolong L-Quad Enhance Filter – Best Quad-Band All-Rounder for OSC Cameras
New Optolong Filter 2-inch L-Quad Enhance Filer Professional L-Quad Enhance Filter (L-QEF)
Quad bandpass Ha/OIII/Hb/SII
2 inch mounted
Near-IR cut to 1000nm
Pros
- Broadest spectral coverage of any Optolong filter
- Suppresses starburst halos effectively
- Near-IR cut-off reduces amp glow noise
- One filter works for galaxies and emission nebulae
Cons
- Less aggressive than L-Extreme on emission nebulae
- Slightly heavier learning curve on processing
- Some users report occasional halos on brightest stars
The L-Quad Enhance is Optolong’s answer to imagers who did not want to choose between broadband and narrowband. It transmits four emission lines – H-beta, OIII, H-alpha, and SII – while cutting mercury and sodium light pollution and adding a near-IR cut-off at 1000nm. In practice that means you can shoot M33, the Horsehead, and even a faint galaxy cluster with the same filter, which is something no other Optolong filter on this list allows.
Optolong’s L-Quad Enhance Filter (L-QEF) is built around a quad-bandpass design with a cut-off depth from OD2 to OD4 and >90% transmittance at the four major nebula emission lines. The IR cut-off is a quiet but important upgrade – it stops infrared contamination from washing out star colours on OSC sensors, which is a real problem on cheaper broadband filters. Several reviewers on Cloudynights specifically praised the lack of IR leakage when stacking long integrations.
Community feedback is largely positive. Shooters with IMX585 OSC cameras report excellent results on both galaxies and emission nebulae, with low haloing around bright stars like Alnitak even at 8-hour integrations. One owner called it “the one to have” for one-shot colour imaging, and another noted that it “blocked out all the light pollution” from his suburban backyard.
The trade-off is a softer hammer against light pollution. Because the L-Quad Enhance is a broadband filter with narrow windows at four emission lines, it does not reject skyglow as aggressively as the L-Extreme or L-Ultimate. In Bortle 9 skies it underperforms the L-Extreme on pure emission targets. A few buyers also report occasional halos on the brightest stars, similar to but milder than the L-Extreme.
For Whom It Is Good
The L-Quad Enhance makes sense if you want a single filter that handles both broadband targets (galaxies, clusters, reflection nebulae) and emission nebulae without swapping filters in and out. It is the best Optolong filter for imagers with varied target lists who shoot from Bortle 1-7 skies. It is also the only filter on this list with an IR cut-off engineered for modern OSC sensors.
If you use an IMX585, ASI2600, or similar modern OSC camera and you want one filter for the whole year, the L-Quad Enhance delivers the most flexibility.
For Whom It Is Bad
Skip the L-Quad Enhance if you shoot exclusively emission nebulae from the worst urban skies. The L-Extreme or L-Ultimate will give you darker backgrounds and cleaner narrowband data. Mono camera users also do not benefit – they should be using individual Ha, OIII, and SII filters instead.
Choosing the Right Optolong Filter for Your Sky
Picking the right Optolong light pollution filter depends on three variables: how bright your sky is (Bortle scale), what camera you shoot with (stock DSLR, OSC, or mono), and what targets you prefer (broadband galaxies or emission nebulae). Below is the framework I walk new club members through.
Filter Selection by Bortle Level
Bortle 3-4 (rural): A broadband filter is plenty for emission nebulae. The Optolong L-Pro will boost contrast on galaxies and reflection nebulae, but you can skip filters entirely on dark targets like M31.
Bortle 5-6 (suburban): The L-Pro and L-Quad Enhance both shine here. Pick L-Pro if you prefer galaxies and clusters, or L-Quad Enhance if your target list mixes emission and broadband objects.
Bortle 7-8 (urban-suburban): This is where dual-bandpass filters earn their keep. The L-Enhance is the budget pick, the L-Extreme is the sweet spot for most imagers, and the L-Ultimate is the premium option for cooled OSC cameras.
Bortle 9 (inner city): You want the narrowest bandpass possible. The L-Ultimate’s 3nm bandpass is the only filter here that consistently pulls clean emission data from downtown skies. The L-Extreme still works but expects longer integrations.
Camera Compatibility
Stock DSLR (Canon, Nikon, Sony A-mount): The L-Pro and L-Enhance are your best options. The L-Pro preserves natural star colours. The L-Enhance gives you narrowband-style nebula images. Avoid the L-Ultimate on stock DSLRs because the 3nm bandpass is too narrow for unmodified sensors.
Cooled OSC (ASI2600MC, ASI533MC, IMX585): All six filters work, but the L-Extreme and L-Ultimate deliver the cleanest narrowband data. The L-Quad Enhance is the most versatile single-filter choice.
Mono CMOS/CCD (ASI2600MM, ASI6200MM): For mono cameras, the L-Pro is the right broadband choice and the L-Extreme/L-Ultimate are useful as light-pollution-friendly dual-bandpass alternatives when you want a single-filter workflow. For serious work, individual Ha, OIII, and SII filters are better.
Target Type Matters
Galaxies, globular clusters, and reflection nebulae: The L-Pro in either size is the best Optolong light pollution filter for these broadband targets. The L-Quad Enhance also works.
Emission nebulae (M42, NGC 7000, Veil, Heart, Soul, Rosette): L-Enhance for budget, L-Extreme for best value, L-Ultimate for premium narrowband. The L-Pro is too gentle on these targets.
Mix of both: The L-Quad Enhance is the only filter on this list that handles both targets from a single filter. Expect slightly more processing effort to balance broadband and narrowband channels.
Sizing and Mounting
Most Optolong filters ship in 2-inch mounted cells, which fit standard 2-inch focusers and adapt to 1.25-inch focusers via step-down rings. If you have a small refractor or a 1.25-inch-only imaging train, the L-Pro 1.25-inch is the only Optolong filter in this list sized for that format.
Check your back focus. Adding a 2-inch filter to a fast f/4 Newtonian can push the imaging train past the focuser’s travel. The L-Ultimate and L-Extreme are both thin enough to clear most focusers, but always measure your back focus before ordering.
Frequently Asked Questions About Optolong Light Pollution Filters
What is the main difference between the Optolong L-eNhance and L-eXtreme filters?
The L-eNhance has a wider bandpass (around 24nm) at H-alpha and H-beta/OIII, making it brighter and friendlier for stock DSLR cameras. The L-eXtreme uses a tighter 7nm bandpass, which produces darker backgrounds and cleaner signal in heavy light pollution but requires longer exposures and a more sensitive camera to perform at its best.
Is the Optolong L-Pro good for galaxies?
Yes. The L-Pro is widely considered the best Optolong filter for broadband targets, including galaxies, globular clusters, reflection nebulae, and comets. It suppresses mercury and sodium light pollution while preserving natural star colours, which is exactly what galaxy imagers need.
What is the best light pollution filter for astrophotography in a city?
For city skies (Bortle 8-9) with a cooled OSC camera, the Optolong L-Ultimate is the strongest narrowband option because its 3nm bandpass produces the darkest backgrounds. For budget-conscious city imagers, the L-Extreme delivers 80% of the performance at a lower price. For stock DSLR city imagers, the L-Enhance is the most practical choice.
What are the key differences between the Optolong Quad Enhance and L-Pro filters?
The L-Pro is a broadband filter that transmits the full visible spectrum except for specific light pollution wavelengths. The L-Quad Enhance is a quad-bandpass filter that only transmits H-beta, OIII, H-alpha, and SII emission lines while adding a near-IR cut-off at 1000nm. The L-Pro preserves natural colours for broadband targets like galaxies. The L-Quad Enhance boosts emission nebulae and galaxies with less aggressive filtering.
Do I need to modify my DSLR to use Optolong narrowband filters?
Not necessarily, but it helps. Stock DSLRs have built-in IR cut filters that reduce H-alpha transmission by 50% or more, which makes narrowband filters like the L-Extreme and L-Ultimate less effective. The L-Enhance’s wider bandpass compensates for this, making it the most DSLR-friendly narrowband Optolong filter. For best results with the L-Ultimate, use a modified DSLR or a dedicated cooled astro camera.
Final Verdict
After months of backyard testing across two OSC cameras and a stock DSLR, the Optolong light pollution filter lineup remains the strongest option for urban astrophotographers in 2026. Our team ranked the 2-inch L-Pro as the Editor’s Choice because it delivers the best balance of cost, versatility, and image quality for the typical city imager. The L-Enhance is the right starting filter for anyone with a stock DSLR who wants narrowband-style emission nebula work. The L-Extreme is the sweet spot for dedicated emission-nebula shooters, and the L-Ultimate is the no-compromise premium pick for cooled OSC cameras in the worst urban skies.
If you are buying your first Optolong filter, start with the L-Pro. It is the filter that will improve the widest range of targets and grow with you as your skills improve. Once you find yourself chasing emission nebulae more than galaxies, add the L-Enhance or L-Extreme to your kit and you will be set for any sky condition your city can throw at you.