Comment by kloch | Hacker News Reader

Comment by kloch | Hacker News Reader

Another issue I didn't see addressed in the article is the anti-aliasing filters on digital cameras. The filters are installed to mitigate Moire when shooting scenes with high frequency (sharp) straight lines

They don't blur like a gaussian filter, they have two separate plates, one that spreads light horizontally and the other vertically, ideally by about 1.0 pixel radius in each direction. This results in "square-like" artifacts, especially if the filters spread by more than 1.5 pixels.

The artifacts are most noticeable in astronomy where there is a dramatic difference between the appearance of star fields with and without anti-aliasing filters.

I don't know how this effect works against film simulation but it probably doesn't help. If they are going to start with Gaussian blur anyway, then using a camera with the antis-aliasing filters removed might help.

Interestingly in the astrophotography hobby space, purpose built, cooled, OSC cameras without aa filters exist around the same price points as DSLRs intended for terrestrial use. To buy one though you really have to be into it (or have a lot of spare cash), as you can only really use it for astro work.

If someone is just getting into the hobby they're probably using a relatively low focal length scope or lens with a DSLR they have laying around. What that means is a wide field shot with lots of tiny stars. Many of those stars might only fit within a single pixel unless they were very bright.

In that specific scenario an aa filter has the advantage of providing more natural star colors, as the light that otherwise might only have hit a red or blue pixel in the bayer matrix is instead spread out into the other colors.

It's less of a beginner thing to do, but if your shots are extremely under-sampled like that, dithering your subframes and using drizzle integration in post helps a lot with blocky (OSC + Mono) and off-color (OSC only) stars. That is, assuming you're trying to stack exposures instead of it being a once off shot.

Do current DSLR models still have AA filters? My Nikon D7100 doesn't have one; I believe the explanation was that it doesn't need one because it's resolution is large enough. In any case that camera never gave me Moiré problems.

I haven't followed the digital camera market in detail anymore in +/- the last decade anymore, so I don't know what's going in regarding AA filters. I just kinda assumed other models would also drop AA filters.

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