What max aperture is the Zeiss.
Do you have a link to a specification?

I have a Sony A77 mk1 which is somewhat worse in low light than a mk2 so gives a guide.

In general terms the A77i is goodish at ISO 800, bearable at 1600 and usable at 2400 or 3200 if you value a usable image over noise. ie 800 would be daytime max if you cared somewhat. More at night may be OK.

If you use a tripod or solidly brace the camera then there is no sensible smallest aperture except for subject movement issues.

For night time street photography or static building shots etc f/1.8 is reasonably useful in a city with shop lights, good street lighting etc if you take great care.

f/2.8 about as good (1.8/2.8)^2 =~ 40% as much light

f/3.5 = 4x less light than f/1.8 = 2 stops and is getting reasonably marginal. Camera can be braced and you can Ninja breathe but any subject movement may reduce photos to more art-statements than records. You will sometimes get 'lucky' with moving subjects, but with the A77 you need as much light as you can manage.

Above that anything can work sometimes.

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As for focal length. For street photography on APSC the 16-80mm is liable to work well in more situations than a 10-20mm. The latter of course has it's place but the wideness limits the range of things it is excellent at. – Russell McMahon 8 mins ago

I have put just a few night-time photos in this album as examples of either Sony A77 or the slightly noisier A700. All relevant settings shown where known.

These were selected by randomly jumping through a "RandomMaybes" folder and stopping at relevant night shots. No merit claimed for any except that I like them for some reason (in most cases :-) ).

http://bit.ly/TWOIFBYNIGHT