SVBony
SVBony SV220 Dual-Band 7nm 2-inch
Two 7 nm windows on one piece of glass, so a single colour camera records hydrogen and oxygen while the city and the Moon are shut out. It is the cheapest honest route into narrowband imaging from a bad sky.
85/ 100
Polaris Score
Our value pick for one-shot-colour narrowband
From$129.99
Where to buy
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01Where it shines
The targets it was made for.
A nebula filter only helps objects that glow at the right emission line — but on those, nothing else comes close. These are the ones it transforms most.
02Be honest with me
What this filter does NOT improve.
A dual-band filter is a specialist. On these subjects it removes light you wanted and gives nothing back, and on one of them it is simply the wrong tool entirely.
✕Galaxies
A galaxy is billions of stars glowing across the whole spectrum. Two narrow windows throw away almost all of that light, so you get a dimmer galaxy and nothing else.
✕Star clusters
Pure starlight again. Every star turns red or teal and most of them disappear. Shoot clusters with no filter or a simple light-pollution filter.
✕Reflection nebulae
The blue haze around the Pleiades is scattered starlight, not emission. It falls entirely outside both windows and vanishes completely.
✕Visual observing
Seven nanometres is far too narrow for the eye. Put this in a diagonal and you will see a nearly black field. Buy a UHC for eyepiece work.
✕Fast optics below f/4
Steeply converging light hits the coating at an angle, which shifts the passband off the emission line. The filter stops working exactly where it should help most.
03Where it fits
Where it lives in your imaging train.
This one never reaches an eyepiece. It threads into the camera train ahead of the sensor, and its 1 mm of optical thickness counts against your back focus.
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04Which filter
How the filter types compare.
A handful of filters cover almost all visual observing. The narrower the band, the more contrast — and the fewer targets it works on.
OIII
Narrowest
Bandpass
~12–18 nm
Best for
Planetary & supernova nebulae
Maximum contrast on the right targets — but only those.
UHC
Broad narrowband
Bandpass
~24 nm
Best for
Most emission nebulae
The versatile all-rounder. A little less punch on Veil-type targets, but works on more of them.
H-Beta
Specialist
Bandpass
~9 nm
Best for
A handful of dim nebulae
The “Horsehead filter.” Superb on a few faint targets, useless on everything else.
Broadband
Light-pollution
Bandpass
Wide
Best for
General city observing
Gently cuts skyglow across the board. Helps a little everywhere, transforms nothing.
This one
Dual-band
Imaging only
Bandpass
~3–7 nm × 2
Best for
Colour cameras on emission nebulae
Two narrow windows, H-alpha and OIII, on one piece of glass. Transformative for a one-shot-colour camera in a city, far too dark to look through.
05The numbers
What These Numbers Mean
BandpassNarrow
7 nm, twice
Seven nanometres out of a 300 nm visible spectrum is how the filter makes a city sky behave like a rural one. It is narrow enough to kill sodium streetlight and moonlight almost completely, and wide enough that you are not fighting the coating tolerance the way a 3 nm filter makes you.
Lines passedThe pairing
H-alpha 656 nm and OIII 501 nm
These are the two lines that emission nebulae actually glow in, and they sit at opposite ends of the visible spectrum. A one-shot-colour sensor records the first mostly in its red pixels and the second mostly in its green and blue, so a single filter gives you two channels from one night.
Focal ratio limitHard limit
f/4 and slower
Interference coatings shift toward the blue as light strikes them at a steeper angle. Below about f/4 the edge of the beam has moved off the emission line and the filter starts blocking the very signal it was bought for. This rules out fast astrographs and every smart telescope.
TransmissionHigh
Over 94 percent in band
What matters in a narrowband filter is not only how much it blocks but how little it costs you inside the window. Above ninety percent means the exposure penalty comes from the narrow bandwidth alone, not from the coating, so five-minute subs stay five-minute subs.
Optical thicknessPlan for it
1 mm
Glass in a converging beam pushes focus back by roughly a third of its thickness. That is a fraction of a millimetre here, which is invisible on a visual scope and matters on a flattener with a 55 mm back focus specification. Set your spacing with the filter in place, not without it.
Optical
TypeDual narrowband
Bandpass7 nm FWHM, each line
PassesH-alpha 656.3 · OIII 500.7
Peak transmission> 94%
BlockingUV–IR, deep
SubstrateWaterproof optical glass
Fit & build
Cell size2″ (M48 × 0.75)
Thickness~1 mm of back focus
Weight50 g
MountAnodised aluminium cell
Focal ratio limitf/4 and slower
UseImaging only
06Pairs with
Compatible gear.
Cameras
One-shot colour benefits most
Cooled OSC · IMX533 / 571
The intended pairing
DSLR / mirrorless
Astro-modified bodies especially
Mono + filter wheel
Works, but separate Ha and OIII is better
Telescopes
f/4 and slower
Imaging refractor · f/5–7
The sweet spot
Newtonian · f/4–5
Fine at f/4, marginal below
SCT with reducer · f/6.3
Long focal length, small targets
Holders
How it threads in
M48 filter drawer
Swap without breaking the train
2″ threaded cell
Screws into most flatteners
Filter wheel · 2″
Carry duo-band and UV/IR together
07Learn more
Guides for nebula observing.
Guide · 6 min
OIII vs UHC: which nebula filter should you buy first?
Most observers start with the wrong one. When the extra contrast of OIII is worth the narrower range — and when UHC is the smarter first buy.
Read the guide →
Guide · 8 min
Why filters do nothing for galaxies (and everything for nebulae)
The physics behind emission lines, in plain English — so you always know before you look whether the filter will help.
Read the guide →