This question already has an answer here:
This isn't a moan - though it easily could be - but is there any real practical use for the high ISO capabilities of modern DSLRs?
Some background, as this is my first question here - I'm very new to DSLRs, having spent the past 15 years since I moved away from 35mm carrying only a phone with me for the occasional snapshot, so I'm very much behind the curve.
I have a Nikon D5500, entry-level but I'm sure sufficient for my requirements for a while yet; kit 18-55mm & a Tamron 70-300mm lens. I am fully aware of their limitations & am prepared to work within &/or around them as much as possible.
I've been using it on full manual since day one. I like to make my own decisions & check the screen afterwards, or even drop the card into my computer & look more carefully; rinse & repeat until I get it right. So much easier than in the wet film days. I shoot RAW & am aware of the possibilities & practicalities of RAW in post.
To the issue...
The entry-level lenses don't have much of an aperture, so I tend to run nearly wide open, which is only f4 at best, to shorten my DOF. Fine for artificially lit work, but I'm outdoors, starting just before sunset in November, in a wood, handheld, at ISO 100. It starts to push my limits for a steady hand as the sun goes down further - I'm OK down to about 1/40s at 70-135mm* on a static subject. By the time it's really getting quite dark I'm already using a flash to lift my foreground & I don't want to try light the scene any more, for practical reasons. I already can't get my flash to go any shorter so I have to be able to get more light in from my background to keep the balance... I reach for the ISO to be able to keep working an extra 20 minutes.
I used to use 32000 b/w back in the day & the results were 'fashionably grainy' but good.
Edit: 3200 not 32000 - which negates that argument, but I'll leave the paragraph in to highlight my earlier confusion.
After comments - I have made comparisons to my old 3200 b/w & yes, the DSLR's noise at matching figures is definitely an improvement.
By the time I get to 8000 I'm really beyond anything even vaguely usable, yet the camera would go on to 26000 or so.
I can't think of a practical use for that speed on the DSLR, the noise is just 'bad', imo, rather than even 'interesting'.
Note; I've experimented with de-noising software & have chosen Topaz as my current favourite, but it has its limits even using that.
So, my question - TL:DR is
Are there practical or artistic uses for high ISO that I have yet to discover, or is it just 'advertising hype'?
I am, of course, aware that my alternative is to light the shot, or get lenses with larger apertures, or take a tripod etc; & also that I'm actually improving SNR by using a high ISO setting, so my question isn't really "How do I fix this?" but "How do I make good use of it in low light, where it [I think] is my only choice to get enough data onto the sensor?", or even an outside possibility of "Is there something I simply haven't thought of?".
I hope this isn't considered a dupe of Is high ISO useful for photography? which I have already read. I'm aware that I'm improving my SNR at higher ISO, but I'm running out of signal against the noise. The accepted answer was also comparing to an underexposed picture, rather than one where there was no practical way to improve the exposure except to use the ISO setting.
Nor a dupe of Reducing noise in very high ISO photos as I'm already using decent noise-reduction software in post.
My further hope to differentiate this as not being a dupe is perhaps to remove the alternative of 'using it to stop fast action in otherwise reasonable light' which leaves me with 'when you run out of shutter speed & aperture & are left with the only alternative being to raise the ISO'.
It does appear to me that a lot of that amplification really isn't helping at that point.
*numbers on the dial, not APS equivalents.
I took some examples as a test.
All using the Tamron 70-300mm lens at 116mm, f4.2
I started at ISO 100 & went up in steps, shortening exposure each time.
On a tripod but it gets very slightly jogged between each frame as I change settings, so they won't overlay.
Images are originally RAW, 6000x4000 but reduced to 30% & saved as jpg.
Images are shrunk on the page using
<img src="" width="200"> but should be viewable at uploaded size by right clicking.
They are all pretty much 'as shot' with a very slight exposure tweak to a couple of them to balance them up.
The little guy pictured is a mask hanging on my workroom wall, light is through the nearby window, cloudy day.
The area of interest is really the top of the little guy's head & the shadow on the wall up & left of that - the low contrast area.
& yes, the guy's made out of wood, on a terracotta-coloured wall - it's not white balance issue, that's what it looks like ;-)
ISO 100 1.0s ISO 400 1/3s
ISO 1000 1/8s ISO 4000 1/30s
ISO8000 1/60 ISO16000 1/100
ISO 25600 1/200s