- Inability to vary exposure times for the various bands due to different signal strengths. Obviously, you're always getting the same exposure times for all narrowbands with this filter. This is a serious issue if you want equally "bright" exposure for the various bands. You can stretch the channels separately, but this creates noise issues. Frankly, this might be the only reason I might use my single narrowbands in the future on certain targets.
- Biggest is simplicity. As I mention above, you can get very good results with one filter, no filter wheel, one set of lights, one set of flats, simple processing, and one focus point (with the caveats above). This not only make things simple - it makes the process faster. It also gets more people involved in astrophotography, which is a good thing for all of us.
- Disk space. Having multiple sets of flats and lights, one for each filter, starts to really add up.
- Cost - this is going to make people laugh, I'm sure. However, compared to my set of Astrodon narrowbands and filter wheel, this filter is much cheaper. I'm sure I'll get arguments that you don't need Astrodons, but I would argue that any set of filters worth having, and possibly buying a mono camera if you don't have one, will be much more than the cost of this filter.
- Speed in autofocus and platesolving - a surprise for me is how short my exposures can be for autofocusing and platesolving, compared to one narrowband. I think this is because starlight comes from four different narrowbands with this filter, and stars are all you care about for autofocus and platesolving. My autofocusing and platesolving exposures with this filter are the same binning and exposure time as I use for Lum or no filter.
If you have a good color astrocamera and want to get into narrowband work, I would seriously look at this filter. Even if you have have narrowband filters and a mono camera, you might be interested. I'm not sure how much use my single narrowband filters are going to get in the future. Frankly, this filter is a lot more fun to use.
Thanks for starting this thread. I have been a user of this sort of multi-narrow band filter for the last 2 years (though not the Triad). But I had the same idea for capturing images with a DSLR using a filter that uses all 4 pixels in the Bayer matrix. The filter I use, is available from Omega Optical and has a 12nm wide HA bandpass and has a 475-500nm bandpass for combined H-Beta and OIII lines. Since it blocks the Hg lamp LP line in the blue/green, but is wider otherwise, I thought it might help me capture more of the blue/green emissions. I thought this might be a good thing bacause OIII and H-Beta lines are quite weak in many emission nebulae and more of the signal in that area might help get a better color image.
For me, this filter has opened up emission nebula imaging with my HA-modded DSLR (Nikon D5300). It has made imaging emission nebulae very simple and processing quite straight-forward. And I like to avoid complexity if possible! Here is an example of the image taken with this filter and my DSLR : The Pelican nebula (post#7 submitted for Goofi's August 2019 challenge). Another example is the recent capture of the Lagoon nebula (M8) :
So, I am a happy camper. There are a few limitations of this filter (and other similar multi-band filters like Triad). One of them, as you correctly point out, is the fact that one cannot selectively change the exposure for different emission lines. Since HA is usually strong in many emission nebula, OIII tends to be much weaker and does not get sufficient exposure time when using this filter. I am thinking of mitigating that by taking additional time on the target using an OIII filter with the DSLR. Obviously, it is not as efficient as when using a mono camera, but still, I think it will help. So, that is the plan going forward. Cheers ..... Anil
Edited by AKHalea, 20 September 2019 - 08:24 PM.