Dark Clear Skies · SVBONY SV220 · W9198A
SV220 3nm H-alpha & OIII
Narrowband nebula imaging in a compact fitting.
Capture two nebula emission bands during the same exposure while rejecting much of the surrounding sky background. This is the 1.25-inch mounted version, W9198A.
The SVBONY SV220 W9198A combines nominal 3nm H-alpha and OIII transmission windows in a 1.25-inch mounted filter. Its 26mm clear aperture and M28.5 × 0.6 male thread suit imaging trains designed around this compact format, provided the opening and cell clearance match your equipment.
- Both emission bands together. Record hydrogen-alpha at 656.3nm and oxygen-III at 500.7nm during the same exposure.
- Narrow windows for nebula contrast. Nominal 3nm passbands reject much of the nearby spectrum; the specified FWHM tolerance is 3 ± 1nm for each band.
- Defined mechanical fit. A 26mm clear aperture, M28.5 × 0.6 male thread and 7mm-high cell let you check your holder before ordering.
What the 3nm design helps you capture
Narrowband imaging selects the wavelengths emitted by glowing gas. The SV220 passes two useful emission regions and blocks much of the unwanted light around them, helping faint nebular structure stand out from the sky background.
FWHM means full width at half maximum: the width of each transmission band measured at half its peak transmission. The quoted 3nm describes a nominal bandwidth, not the thickness of the glass; SVBONY specifies 3 ± 1nm per passband and a 2.0mm substrate.
SVBONY rates the OIII/H-alpha average peak transmission at ≥85%, with average OD5 out-of-band blocking across its specified 300–1050nm blocking range. These ratings describe the filter; the final image also depends on the telescope, sensor, sky and capture technique.
A specialist filter for emission nebulae
Choose emission-rich targets
The SV220 suits emission nebulae, planetary nebulae and supernova remnants that emit H-alpha and/or OIII light. Subjects such as the North America Nebula, the Veil complex and the Dumbbell Nebula give these passbands useful work to do.
The balance of red hydrogen and blue-green oxygen varies from object to object, so different targets will respond differently.
Plan a broadband approach for other subjects
Galaxies, reflection nebulae and star clusters emit much of their light across a broad spectrum. A narrow dual-band filter rejects a large part of that light, so it is not a general-purpose filter to leave in place for every target.
You can still collect separate narrowband data to emphasise emission regions in a galaxy, then combine it with suitable broadband imaging.
Moonlight and city skies still matter
The narrow passbands can help with unwanted background light, but they do not make a bright moonlit sky equivalent to a dark site. Choose a suitable target and plan enough total integration time.
Check the thread, holder and sensor coverage
This version has a single external M28.5 × 0.6 thread. Use a drawer, wheel or holder intended for a 1.25-inch mounted filter, and allow clearance for the Ø31.75 × 7mm cell. A camera’s M42 or M48 connection alone does not establish which filter cell its holder accepts.
The 26mm clear aperture needs checking against the sensor dimensions, filter-to-sensor distance and working focal ratio. It can suit compact imaging trains, but do not assume it will illuminate the corners of a larger sensor in every arrangement.
Check the whole light path
A narrow adapter or holder can restrict the field even when the filter itself is large enough. Check all openings between the telescope and sensor, and follow the optical system’s back-focus guidance.
Need a larger clear opening? Compare the 2-inch SV220 3nm W9198B, subject to the holder and optical geometry of your system.
Match the filter to your camera and focal ratio
One-shot-colour astronomy cameras: both emission bands reach the sensor during the same exposure. With suitable processing, the red and blue/green channel information can be used for an H-alpha/OIII nebula image or an HOO-style colour combination.
Monochrome cameras: the filter passes both bands together, so one exposure combines their light into a greyscale image. Use individual narrowband filters when you need separately controlled H-alpha and OIII datasets.
DSLR and mirrorless cameras: check the mounting arrangement and your camera’s H-alpha sensitivity. A camera’s internal filter can reduce the red nebula signal; an external SV220 cannot restore light already rejected inside the camera.
Fast optics need a specific compatibility check
The 3nm windows are sensitive to the angle of the incoming light. A fast telescope or focal reducer can shift the transmission bands and reduce useful H-alpha or OIII throughput. Ask us to check systems working at f/5 or faster; do not assume this standard filter is suitable for an f/2 RASA or HyperStar configuration.
A physical fit and an optical match are separate checks. The telescope’s working focal ratio with its reducer installed is the figure to use when discussing suitability.
SV220 7nm or 3nm: which should you choose?
Both versions record H-alpha and OIII. The difference is the width of the transmission windows around those emission lines.
| Buying consideration | SV220 7nm | SV220 3nm |
|---|---|---|
| Bandwidth per emission band | 7nm FWHM | Nominal 3nm; specified 3 ± 1nm FWHM |
| Main reason to choose it | A broader passband and an accessible route into dual-band nebula imaging. | Narrower windows to reject more surrounding sky background, when matched to the optical system. |
| Fast telescope check | Required: this is not a dedicated high-speed filter. | Especially important because the narrower bands are sensitive to optical band shift. |
A narrower bandwidth does not automatically mean shorter exposures or a better result in every setup. Telescope speed, filter transmission, sky brightness, target emission and processing all contribute.
See the SV220 7nm filter in both sizes for the broader-band option.
Set up and capture with confidence
- Confirm the mechanical fit. Match the filter thread and cell clearance to the holder. The nominal filter size is not the camera connection thread.
- Check the complete optical train. Include any reducer when checking focal ratio, and follow the telescope or flattener manufacturer’s back-focus guidance. Filter glass thickness and holder length are different measurements.
- Refocus with the filter installed. Use a test frame to check focus, background level, bright-star saturation and illumination across the sensor.
- Calibrate consistently. Capture suitable flat frames with the same filter and optical arrangement used for your light frames. Build total integration time around the target and conditions.
Technical specifications
| Specification | W9198A · 1.25″ · 3nm |
|---|---|
| Brand / model / SKU | SVBONY / SV220 / W9198A |
| Mounted format | 1.25-inch |
| Filter type | Dual-band H-alpha and OIII imaging filter |
| Nominal centre wavelengths | OIII 500.7nm; H-alpha 656.3nm |
| FWHM bandwidth | OIII 3 ± 1nm; H-alpha 3 ± 1nm |
| Peak transmission | OIII/H-alpha average ≥85% |
| Specified blocking range | 300–1050nm, outside the intended transmission windows |
| Out-of-band blocking | Average OD5 |
| Clear aperture | 26mm |
| Mounting thread | M28.5 × 0.6; single male thread |
| Cell diameter × height | Ø31.75 × 7mm |
| Substrate thickness | 2.0mm |
| Cell material | 6061T aluminium |
| Surface quality | 60/40 |
| Parallelism | 30 arcseconds |
| Manufacturer-listed net weight | 7g |
Optical ratings and dimensions are manufacturer specifications. Substrate thickness is the glass thickness; it is different from cell height and from the optical length of a complete filter holder.
What is included?
One SVBONY SV220 1.25-inch mounted 3nm H-alpha/OIII filter (W9198A).
The telescope, camera, filter drawer or wheel, adapters and any additional filters are separate items. Equipment shown in manufacturer compatibility illustrations is not included with this filter.
Practical questions before you buy
Can I use it under a bright Moon?
It can help separate nebula emission from unwanted background light, but moonlit conditions still affect the result. Keep your expectations, target choice and total integration time appropriate to the sky. A darker sky remains useful.
Does one filter give me a complete SHO image?
This filter records H-alpha and OIII. A three-channel SHO dataset also needs independently captured SII information. HOO typically maps H-alpha to red and OIII to green and blue. SHO maps SII, H-alpha and OIII to those three channels respectively, so it requires additional sulphur data.
What exposure time should I use?
There is no universal exposure time. Start with settings appropriate to your camera and telescope, inspect a test frame, and adjust for background level, star saturation and tracking. Total integration time matters as well as the length of each exposure.
Will every bright star be free from halos?
Halos and reflections depend on the filter, bright star, camera window and the rest of the optical train. Results vary between imaging systems, so halo-free performance cannot be guaranteed.
Is this intended for visual observing or the Sun?
The SV220 is an astrophotography filter. It is not a solar filter and must never be used as solar protection.
Choose a filter that fits your imaging setup
Tell us your camera, telescope, reducer and filter holder. Dark Clear Skies can help you check the size, thread and working focal ratio before you order.
Ask DCS about compatibility
