Where are Chroma's made?
My only complaint on the Chroma is the size of the filter is too wide. That makes it more difficult to use. I mostly use it for 1x observations.
Chroma's are made in Vermont; it's an employee owned company. Agreed, their filter cells are extaordinarily long. It has been posited by some that Chroma actually makes filters for Astrodon (now owned by Far Point Astro). I previously sent my Astrodon 5nm filter to Gavster, since he had the 5nm Chroma for a direct comparison of the two filters. He found little if any discernible difference.
I too have found subtle differences between filters of differing band pass. Between a 6 Astronomik and a 7 Optolong, I see no useful difference with my optical systems, under my skies. Between an 8 Chroma and 7 Optolong, likewise almost no distinguishable differences. Even between a 5 Astrodon and the 7 Optolong, the differences were subtle (see this comparison between a 5 and 7nm in 3 different scopes:) https://www.cloudyni...astronomy-r3135
But between a 6-7nm filter and the 3.5nm Antlia, I do see distinct improvements in nebular contrast. That contrast improvement comes at the cost of star attenuation and the special type of vignetting from band shift. Stated many times previously, there is a difference in what filters are most useful for visual use as compared to photography... even with a phone camera. For visual H-a use, I have settled on 12, 7 and 3.5nm. Use of these filters depends on which scope I'm using, how much LP is present and how bright the H-a subject is.
For imaging with NV, I now have five H-a filters. My plan is to sell two... after I have explored what each one does with my imaging optics. I had the Astrodon 5nm but sold it, actually preferring the Optolong 7nm filter most of the time. But now I have a Chroma 8 and an Astronomik 6 to compare against the 7. What I am sure of, is keeping the 3.5 and the 12nm filters. What I'll decide is which of the 6, 7 or 8nm filters I will keep for imaging.
I don't think it can be overstated how differently these filters react to local sky conditions (degree of LP), optical aperture and focal ratio. Vignetting from band shift is tolerated differently by observers and personal preference may steer a user to less star attenuation. There's really no way of knowing which filter you will prefer unless you try them. But between filters of 1nm difference, the changes are so small that it seems unlikely you will detect them except on very specific H-a subjects. A larger aperture might make it easier to see differences, but my experience with modest apertures (3" to 8") has shown subtle if any noticeable differences.
I have been asked why I keep a 12nm filter when a 6nm or 3nm show nebulae so much better. My answer is the 12nm shows much less band shift (vignetting) and more stars... and it makes the nebula appear more as a translucent gas than as a solid mass. This is a choice based on personal preference. But if I'm tracing faint nebulae, I'm much more likely to use the 3.5nm so I can actually see it. My experiment on Sh2-27 showed that the 7nm barely revealed this nebula as a non-specific blob, whereas the 3.5nm filter revealed detail, showing the massive face I dubbed as an Ork (currently, the first photo in my gallery). This was from a blue zone site in CA... from a black site, like I sometimes visit in Nevada, the 7nm or a 6nm filter might have worked fine in revealing detail... because of less light pollution which allows for greater contrast using a wider band pass filter. From my red zone home, Sh2-27 is basically invisible with any filter.
Edited by GeezerGazer, 17 August 2020 - 01:58 PM.