From an astro perspective...

[Downunder]

The camera industry is still welded onto the past - clinging to ISO, shutter speed and f/ratio. But these concepts all stem from the film era.

There is another small niche market - astro cameras - which use the same sensors as consumer cameras, but take a very different (clinical) approach based on how these sensors actually work, noting that CMOS is essentially linear, whereas the exposure response of film is highly non-linear. Perhaps in 10 years time we'll be talking about gain and exposure duration, instead of ISO...

 

[BuckeyeSkyGuy]

I agree that ISO is largely an afterthought for astro. It's all about the sensor's dynamic range, quantum efficiency and presence/absence of amp glow on long exposures.

I shoot with a modded D5300 Nikon that you buy so cheap these days, a used 135mm Samyang/Rokinon likely nets more on the used markets. But the Sony IMX-193 sensor has good dynamic range, it's largely ISO-invariant (I typically shoot 400 or 800 ISO) and when coupled with that 135mm Samyang f/2 lens...look out. It'll make even an absolute beginner look like a pro if they've got a decent star tracker to put it on.

I hear people say all the time, "astrophotography is expensive!", not thinking about how expensive WILDLIFE photography can get with a 500mm - 600mm f/4 prime. I prefer to pay for my optics with cash or checks, not HELOCs.

And that's actually one nice thing about astrophotography--most of the expensive bells and whistles modern camera bodies have to justify their stratospheric price levels simply aren't needed for astro. Heck, you don't even WANT autofocus. A good telescope to hook it up to can easily be found for $1,000 USD or less. ALL forms of photography are ultimately results-oriented enterprises. Proof is in the pictures. If it works, then in the words of James Hetfield, "nothing else matters."

 

[Downunder]

Would not use a DSLR. You really need to look at what's possible from the CMOS astro cameras (ZWO in particular). The huge thing is the use of a TEC cooled mono sensor combined with narrowband filters which produce amazing results even in suburban skies, and a camera were RAW does mean the real sensor output, no compression, no fiddling in camera by software, as a straight PNG.

You simply cannot do similar with a DSLR equipped with a Bayer (RGB filter).

 

[BuckeyeSkyGuy]

I have an astrocamera, though it's OSC. I've got the ZWO ASI533MC-Pro. Works great for my Bortle-6 skies and the occasional travel to nearby Bortle-4 and -5 skies. Back-illuminated, cooled astro cameras are, yes, much better for astro than DSLRs or MILCs. The QE gain alone makes the change worth it.

As few clear nights as I get, I don't want to make the transition to mono astro cameras. Too much of a PITA Factor and too high a chance I'll only have some of the channels on a southerly object (i.e. NGC 253) I might get one or two cracks at in a given year.

DSLRs and MILCs still have their place when it comes to wide-angle, nightscape shots or when used with short telephoto lenses. My modded D5300, the 135mm f/2 Samyang and a Star Adventurer are capable of some amazing shots under dark skies.