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I've been enjoying Marc Levoy's Lectures on Digital Photography and have reached this point.

Marc has broadly said:

• Sensors have got better at reducing noise


• But pixels are gotten smaller so there is more noise


• These effectively cancel each other out.

Unfortauntely his chart stops at 2008.

I've been unable to find an updated version of this chart. Does the SNR still remain constant when we add sensors up to 2018? (not counting downsizing, which he goes on to)

This data was iffy then — not really enough data points, and the trendline is dubious:

_{Source: a very timely xkcd}

That said, the company DxOMark does measurements of camera sensors all the time, designed to be resolution-neutral. Here's a chart of the "Sports" score, which is based on SNR, from all tested APS-C camera models from 2002 to 2018:

Given the cartoon above, I won't try to draw a line, but

1. It's pretty clear that there's a slight upward trend


2. That trend might not have been obvious in 2008, but it seems like it's probably actually also there.

If you look at overall scores for the same cameras, which include dynamic range and color depth, you'll see the same general sort of upward trend, although it's arguable that there's more growth to around 2010 after which it kind of levels off.

In practice:

1. 
   All cameras over the last decade do very well on these measurements.


2. More megapixels don't seem to be hurting.
   


3. There are cameras within any given year's cohort which would fit right in ten years later or ten years earlier. That is, waiting until next year is unlikely to give you a see-in-the-dark miracle.


4. 
   Don't worry too much about this. All of the cameras produce excellent results even in very, very little light.


5. None of these measurements really matter to making good photographs.

It seems that, in general, most camera makers have been content to trade most, but not quite all, of the gains they've made in terms of sensor efficiency in exchange for more megapixels with roughly the same overall performance with regard to signal-to-noise ratio as their older, lower resolution sensors had.

There are some notable exceptions in terms of specific models. But when that is the case, there are often two similar models offered, one with higher resolution that means lower SNR at the sensel (pixel well) level and the other with lower resolution but larger sensels with better SNR for each discrete photosite.

Take for example the first generation Sony α7 model line, which had three different versions:

• The high resolution α7R has a 36.4MP full frame sensor


• The balanced α7 has a 24.3MP FF sensor


• The high sensitivity α7S has a 12.2MP FF sensor

The second generation of the α7 model line was similar, with 12.2MP, 24.3MP, and 42.4MP sensors inside the α7S II, α7 II, and α7R II, respectively. So far we've seen two models in the third generation: the 42.4MP α7R III and the 24.3MP α7 III.

Note that often manufacturers will continue to use sensors that were "cutting edge" when introduced in an upper tier model. Later models lower in their product range will get what is essentially the same sensor. Perhaps the classic example would be the 18MP APS-C sensor first introduced by Canon in their original 7D back in 2009. It has appeared in numerous models since, including the basement entry level Rebel T6/1300D that was rolled out seven years later in 2016.