Previously I mostly used a modified full-spectrum Canon 6D. I now have an ASI1600MM-C with the EFW7 and 36mm ZWO filters. Here are some of my images with this setup. These are literally the first LRGB and NB image I have ever taken.
I love my ASI1600 and really see the advantage of a mono camera in spite of the image processing learning curve.
I have really wanted to do this post and find out what do you get for more expensive filters and I ask to please show examples to demonstrate why they are better. I honestly don't know what people are seeing that would justify spending 3X the price. I really would like a clear answer.
I have a PHD in physics with specialty in infrared and pulsed laser optics. I also worked at the advance photo source and know a fair amount about x-ray optics. I have build entire optics labs. I have looked at the specs for the various filter manufacturers. I have seen no claim on their web site for differences that would justify improved imaging.
The narrowness of the bandpass for the NB filter is about the only thing that i can see as a big driver for the cost and that makes sense. It is much more difficult and expensive to narrow the bandpass requiring significantly more multilayer interference coating layers. However, at least from my experience in an orange zone, unless you are in seriously heavy light pollution or imaging at the full moon, its not going to buy you that much. The flatness of the filters from an interference point of view might be a big deal, but I dont specs stating that as a difference nor is there really much difference in peak transmission. There might be some significant engineering for high off axis transmission characteristics for very high F ratios, but again there are no claims for technology advantages. For LRGB, matching to be a parafocal set is an advantage but if you have doing autofocus with SGP, then that doesn't matter either. IF there is som thing with respect to color balance matching, I could understand that, but we all digitally process our images, so why is that so important. We do so much washing of the data for sharpness and other characteristics how does the filter quality differences play a role.
Anyway, Is there a reason for spending more on one filter over another? - I cant really come up with an answer. I did however, go with larger filters since I do have a full frame camera and have fought vignetting issues to death so I spent more for the 36mm. Maybe I wasted my money, but it was mine to blow.
I think that I get good imaging with the ZWO filters and they are not what is limiting my image quality. Will that situation change - I COULD ONLY HOPE SO. If my filter quality was what was my limiting factor for my final images - that would be awesome. That would mean that the huge number of issue other than filters that I currently KNOW are causing me problems would all be fixed!! I would love to just throw money at this and get better results. For me at this point, I would always go for a better mount if I have money to burn on this - that always seems to pay off. Or buy darker skies and fewer clouds.
So now, if you have some technical defensible reason and hopefully can demonstrate with data, please reduce my ignorance. If you just think that your image look better when you forked out for Astrodons - that is a perfectly reasonable answer. In the end, it all comes down to how much we enjoy the pictures that we create.