Baader 6.5nm Narrowband Filter-Set – CMOS-optimized (H-alpha / O-III / S-II)

For an extremely fast aperture ratio, you will inevitably need filters with pre-shift. Our standard 6.5nm and 3.5/4nm ultra-narrowband filter series work with full transmission up to an aperture ratio of f/3.4.

So for your TAK180, you will require a Highspeed Filterset with pre-shift. Our 6.5nm series is designed for normal aperture ratios from f/3.4, and the Highspeed series is designed for optics faster than f/3.4. Due to the very narrow FWHM of 3.5/4nm, our Ultra-Narrowband series requires a more precise subdivision for f/2 systems up to f/2.3 and f/3 systems between f/2.3 and f/3.4.

You can therefore choose between the 6.5nm f/2 Highspeed series and the 3.5/4nm f/3 Ultra-Highspeed series. The 6.5 nm series is usually sufficient for your Bortle 4/5 sky. However, if you want even higher contrast and suppression of unwanted light pollution, we recommend the 3.5/4 nm f/3 series.

The following filter sets are suitable for your setup:
- 6.5nm f/2 Highspeed (from f/3.4 and faster): https://www.baader-planetarium.com/en/baader-6-5nm-f-2-highspeed-filter-set-cmos-optimized-h-alpha-o-iii-s-ii.html
- 3.5/4nm f/3 Ultra-Highspeed (from f/3.4 to f/2.3): https://www.baader-planetarium.com/en/3-5-4nm-f-3-ultra-highspeed-filter-set-cmos-optimized-h-alpha-o-iii-s-ii.html

If you are unsure which filter set is suitable for your setup and aperture ratio in the future, we have developed a straightforward narrowband/high-speed filter selector for our Baader filters: https://www.baader-planetarium.com/en/baader-narrowband-highspeed-filter-selector/

 

With your f/4 Newtonian including the f/3 reducer, you are exactly at the limit where our normal narrow-band filters no longer work with full transmission. These are only designed for a focal length of slower than f/3.4. For full transmission you will therefore need the 6.5nm f/2 highspeed version. You should therefore decide in advance whether you want to use your Newtonian at f/3.0 or f/4.0 and buy the right filter set accordingly. Otherwise you will need 2 full filter sets to be able to utilize the full transmission.

Of course, our narrowband filters can also be used with a color camera, but there are some trade-offs. You will definitely sacrifice some resolution for the flexibility of an One shot color camera (which is ideal for EAA and planetary imaging - DSO, not so much). For narrowband, the sensitivity reduction of an OSC camera compared to a monochrome is a direct result of the Bayer matrix. Bayer matrices are usually RGGB, so only 1/4 of the sensor picks up Ha radiation through the red filter. With OIII, you're a little better off - it will be about 1/2 as sensitive as a monochrome camera with the same sensor. The real problem comes with SII. It's in the far red, and the red filter in a Bayer matrix will attenuate some of that radiation. Also, SII is generally quite weak in DSO targets to begin with. So using an OSC camera with an SII filter can require some pretty massive integration times to get enough SNR to make a nice image. So it's not that you can't do it - you can. But you're essentially giving up a lot of imaging time by choosing an OSC over a monochrome camera for DSO narrowband imaging. If this is going to be an occasional pursuit and you don't have heavy light pollution, then the OSC makes sense. If you're in heavy light poulltion and you're going to be doing mostly narrowband imaging, then it makes a lot more sense to get a mono camera.

Yes the filters fit in the ZWO filter wheel

Yes, every filter moves the focus by ca. 1/3rd of its thickness outwards. That's why there are Luminance/clear glass filters e.g. for focussing, too. This focus shift should be taken in account when the filter is between e.g. a reducer/corrector and the camera sensor. So, you should take it into account.

Yes this is the right choice!