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I recently purchased the ZWO 1.25″ narrowband filter set. The set include 3 filters H-alpha, S-II, and O3.
Narrowband filters are a great way to battle light pollution when photographing emission nebula. I live in a Bortle 8-9 area so for me narrow band is a must have. Even in light polluted skies, you can achieve highly detailed color images with a monochrome camera.
Specifications
Thickness – 2mm (glass)
Cost – $369 as of post date
Light Pass – up to 90% (see chart) The manufacturer says “up to 80%” but if you look at the chart, it clearly say 90%. I suspect it’s just a typo on their site since the chart is more reliable.
Band Pass – 7 +/- .5nm
Wavelength
H-alpha – 656nm
S-II – 672nm
O3 – 500nm
Mounted – yes (standard 1.25″ filter thread male)
Installation
The filters are pre mounted onto standard 1.25″ male filter threads. I have used them individually and also with the ZWO Filter wheel. All you have to do is to screw them into the filter holder.
Performance
The following images were taken in my back yard using all three of these filters.
Camera – ZWO 1178mm
Mount – Skywatcher EQM-35 Pro
Guide Software – AsiAir Plus
Guide Scope – SVBony SV165
Customer Reviews
Agena AstroProducts has a rating of 4.3 stars with 6 reviews.
High Point Scientific has a 5 star rating with 2 reviews.
Most of the feedback posted from customers has been positive. The 4 star ratings mention difficulty focusing and not fitting the filter wheel. For me they fit perfectly so I cannot replicate any issue that the customer mentioned. As far as focuing goes, I can attest that it is more difficult to focus with the filters. The issue is that there is a significant reduction in the amount of light passed to the camera. To overcome this, I use a 15 to 30 second exposure time in the focus and preview mode. With the addition of a Bahtinov mask, I can use the preview function with long exposure to fine tune the focus.
Focusing
As I just mentioned, focusing is a challenge. Here is how I get to focus fast with my setup. I use a filter wheel with my kit. I bought a cheap CLS filter and added it to the wheel. To get close but not yet perfect, I just switch to the CLS filter and increase my exposure time to 2 to 5 seconds. This get’s me very close to what the narrow band filter need to be at.
After this step, I switch to the filter I intend to use and use the preview mode with 30 seconds. With the mask, I can achieve perfect focus this way.
