How do you manual focus wide angle cityscapes at night?

[jdong217]

I have the Tokina 11-16mm/2.8 but shoot with a D3100 so I can only manual focus. I'm a pretty far distance away but just leaving the focus at infinity doesn't really give me the most focus. Should I select my focus point to be something in the middle in terms of depth? I was shooting in pretty low light so my camera wasn't really doing a good job of letting me know when I was in focus. I really want to upgrade to D7000 if only for the AF motor. Here are two examples:

they look ok at medium size, but large and beyond are bad. also, why is there so much noise even at ISO 100?

#1 don't mind the overexposure. the front row is so hideously OOF to me...

#2 the first night i have seen blue sky AND a full moon over hong kong

 

[dots]

What aperture and shutterspeed are these ? The lens is very wide..try f16 at infinity.

 

[jdong217]

Oops, sorry:

#1:
Exposure: 30
Aperture: f/8.0
Focal Length: 15mm
ISO: 100

#2:
Exposure: 15
Aperture: f/8.0
Focal Length: 13mm
ISO: 100

 

[KenC]

Re the focus, read up on hyperfocal distance. At each aperture there is a distance at which the lens can be focused with the depth of field extending to infinity.

 

[Derrel]

No, do NOT focus on the "middle"...as you can see, at larger sizes, the incorrect focusing point shows up. Focus on the FAR distance that is appropriate, nit a close distance, and not a hyperfocal distance. Use either live view, or LCD review of captures you've made, and verify good focus by zooming in on a point light source and examining it for good detail. You will find that the absolute "best focus" is obtained by focusing in the zone where best focus is desired, and that hyperfocal distance focusing will cost you sharpness on the distant parts of a 'scape.

 

[DiskoJoe]

The noise is probably from air pollution. HK has notoriously poor air quality. You have to wait for a night where the wind whips through to blow all the pollution away.