Hypothetical question about lower iso vs built in nd filters

[Unframed Dave]

This question follows a discussion last night / morning with a mate on the other side of the world.

He's an om1 user (bless) and considering the latest version. We were discussing the "built in" ND filters.

It lead me to ask myself why camera manufacturers don't offer lower iso ratings. On the face of it to a simpleton like me, it seems quite plausible.

So why isn't it out there? I'm sure there's a good reason.

 

[FowlersFreeTime]

I'd be curious to know. The a6000-a6600 had a lowest ISO of 100, but now my a6700 has ISO 50. Haven't used that setting yet, might come in handy with this month's long exposure challenge.

 

[Alan Clark]

Perhaps it is impossible to have an ISO much less than 100? When the data are read from the sensor they are amplified electronically by an amount determined by the ISO before being converted from analogue to digital, but the amplification factor cannot be less than x1. (I am guessing that this is the explanation).
The "Built in" ND filter works by taking a series of short exposures (ignoring the light between exposures) and combining them, which gives a different effect from real ND filters, and does not allow more extreme degrees of filtering, so I don't think it is a particularly good idea.

 

[Richard A]

My Sony RX100 MIII has a built in neutral density filter. I think it’s mainly included for using with video. I can’t remember ever using it. It also has ISO settings below the base ISO which is 125.

My Sony A7R5 has a base ISO of 100 but also has ISO 80, 64 and 50.