http://www.chuqui.com/2012/09/something-id-like-to-see-in-cameras-going-beyond-high-iso/ Stories Told Here Sat, 18 May 2013 22:23:00 -0700 hourly 1 http://wordpress.org/?v=3.5.1 http://www.chuqui.com/2012/09/something-id-like-to-see-in-cameras-going-beyond-high-iso/#comment-1967 Josh Marshall Tue, 11 Sep 2012 07:16:00 +0000 http://www.chuqui.com/?p=17955#comment-1967 It’s an electrical engineering / chip design and technology challenge. A sensor will have a “native” ISO where there is no analog amplification of the signal, this is the lowest non-expansion ISO, usually 100 or 200. All the higher (non-expansion) ISOs are then amplified from this native/base ISO, you are multiplying the signal.
These amplifiers need to be as low-noise as possible to get clean high-ISO. IIRC, it’s very hard / impossible to make an analog amplifier that will *divide* (as well as multiply), which is what would be required for ISOs below the native ISO. This is why ISO 50 is usually an expanded ISO, the signal is divided by 2 digitally, so you’re losing highlight range.
Of course, it could somehow be done through extra electronics (a second amplifier circuit that can be switched in)… but that, by definition, will introduce more noise.
So yes, in theory it is possible… I would say it hasn’t been done because the tradeoffs aren’t worth it (yet).

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