From f/5.6 to f/22

[DanK]

Which series looks most "natural"?
2.8 5.6 11 22
2.8 5.7 11 22
2.8 5.7 11 23
2.8 5.6 11 23

They both look natural to me, but looking at what you posted, I think you may have put your finger on it.

An increment (decrement) of of two stops will always double (halve) the f/stop value. This is readily apparent when you start with any integer value. It isn't always apparent when you start with a non-integer value (e.g., 2.828...), because sometimes rounding will cause the higher number to increment by 1. If you round those cases down (5.656854 => 5.6), then increment of two stops, when rounded, will still look like a doubling--as it would if not rounded as much.

If that's what you meant by looking natural, it seems like a possible explanation to me

[miatab]

I'm dazzled by all of this, and unless you lighten up I'm going back into the cave.

[pnodrog]

I'm dazzled by all of this, and unless you lighten up I'm going back into the cave.

Through the ages cave drawing has always been held in far higher regard than photography.....

[miatab]

Yes, particularly throughout the stone age.

[NorthernFocus]

Of course, no one has gotten into discussing the T-stop, which is used in cinematography. The "T" stands for "transmission".

The f-stop is purely a mathematical ratio of the focal length to input aperture, so it is really an "ideal value". The T-stop (or T-number) goes further and actually measures the drop in light level that comes from some of the light being absorbed by the glass lens elements. This will of course vary from lens to lens. The T-stop / T-number will always be larger than the f-stop; i.e. a f/2.8 lens could be a t/3.5 lens.

This is very evident in some lenses if compared side by side. At one time I owned both a Nikon 200-400mm f4 VR and a 300mm f4D. I read somewhere that in spite of the claimed f4 that the 200-400 actually had a T-stop of about f5. It was quite evident that the 300mm prime was MUCH brighter looking through the VF than the 200-400 was. The reason is readily evident, The 300mm has 10 glass elements while the 200-400 has 24 elements. That is one downside to zoom lenses. They tend to have more glass in them than prime lenses of comparable focal length/aperture.