Considering updrading from RX100 to NEX-5N or NEX-6

10mm * 2.8 = 28mm   (2.8 is the crop factor for the RX-100.  Actually, I thought it was 2.7, but it doesn't matter for our purposes.)

The NEX crop factor is 1.5, so you want 28mm / 1.5 = 19mm to achieve the same field of view.

You can get that with either kit lens at about f/3.5 - f/4.  I don't have either in front of me.

You can get at least 2/3 of a stop more light with the Sigma 19mm/2.8 EX DN.

Or with the Sony 16/2.8 E lens, which is equivalent to 16mm * 1.5 = 24mm.   The 16/2.8 E is a good bit smaller than the Sigma 19/2.8.

Depending on how good PDAF turns out to be -- reports are mixed -- you might get more in-focus shots with the 5R or 6.

Or you can get low-light performance that's every bit as good as the 5R or 6 very inexpensively in the 5N which is now deeply discounted.

So maybe a 5N with a 16/2.8 E is the least expensive way to go.

That said, the Sigma 19/2.8 is a really nice lens, very sharp with great color and contrast.  People will tell you not to use it for people shots, but you just have to keep the person near the center of the frame and watch for things like elongated noses if you get too close.   I use mine for portraits frequently.

Or the 5R or 6 with the kit and either the Sigma 19mm or Sony 16mm.

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