Any reason why cameras don't have ISO 10 or 5 or even 1?

You can imagine it to be "1" in your head if it makes you feel better.

>>2945407
Well that's not entirely true, the S in ISO stands for 'standardisation' for a reason.

>>2945401
The sensor has its maximum sharpness/minimum faults at ISO100, so it's impossible as this is directly linked to light sensitivity. Higher ISO values don't make the sensor really more light sensitive, it tries to amplify the information available and interpolates the image.

There are some cameras with 50 ISO, 25 ISO...

>>2945401
technological limitations.
there are dmf backs with ridiculously, stupidly low ISO. but mass production cameras don't need low ISOs because at 30mp they're noise free with retarded dynamic range up to 800. so why raise the price of the camera to go lower? use an ND filter if shutter speed is the answer.

>>2945422
software ISO's, it's just underexposed ISO100 shot.

>>2945401
100 is (nominally) the native iso. Theoretically having a lower iso would be the same as just having shot the image at 100 and then pulled it down in post. It'd be pointless to have an in camera pretend option that just remapped values in this way. The D810 has an iso 64 but it too has decreased (but marginally through ADC and sensor magic) dynamic range.

To achieve a lower iso for regular sensors you'd basically have to make the sensor less efficient in general, which would significantly harm the rest of the iso range.

>>2945401
A sensor consists of photosites that convert light to charge, a fixed amplifier, a variable amplifier to achieve different ISOs, and ADCs that convert that charge to numbers.
At the so-called "base" ISO, there is no variable amplification done. To make this base ISO lower (= to be able to process a bigger charge), you have to make the input range of the ADC bigger, or the fixed amplification lower. But then, at higher ISOs you'll have to apply higher variable amplification, which will increase noise and lower DR. It's also difficult to build a quality amplifier capable of 100x variance (note that most cameras use analog amplification up to ISO 1600 or so; higher sensitivities are achieved by digital scaling and often marked "Hi1", "Hi2" etc.)

tl;dr with a lower base ISO, quality at higher ISOs suffers.

Also, not every camera has ISO 100 as base; a lot of crop CMOS sensors have a base ISO of 200.

>>2945485
you mean overexposed

>>2945508
>decreased
You mean increased

>To achieve a lower iso for regular sensors you'd basically have to make the sensor less efficient in general, which would significantly harm the rest of the iso range.
It depends on the tech, with CCD you can pull the readout on them waaay down to ISO35, like on the Phase One 80mp backs. It produced an impressive 13.5 stops DR back in the day, but Sony has managed to achieve better at ISO100 with CMOS, the latest 51mp sensor is like 15 stops.