I've started taking a lot of night photographs recently on a tripod with my Nikon D7100. After entering a challenge on the D7100 forum of DPReview.com someone suggested it might be interesting to see my process. I'd not thought of writing it down before and I found it useful; hopefully you will too. It is rather long.
o a Nikon 16-85mm lens and a Tokina 10-16mm f2.8 Pro (uses focus motor in camera which seems to sap batteries)
o a ML-L3 infra red remote
o 1 or 2 extra batteries
o a powerful torch. I currently use a LED Lenser M7R Rechargeable Torch which can project quite a lot of light on a subject at some distance. There are torches which can project more light at further distances but this one is relatively small and light and easily fits in my pocket.
o tripod - I hate carrying around a heavy tripod even though I know the benefits of a more robust tripod. I currently mostly use a Manfrotto befree MKBFRA4-BH because it folds up small and is light. The main disadvantage other than stability is the height isn't so good and I sometimes find myself behind a wall where the only way to get the camera over the top is to extend the centre section and to rest the tripod on 2 legs up against the wall. Ideally, I'd like more height.
The basic settings:
o Long exposure noise reduction turned on or you'll get "hot" pixels in the final image. The negative side of this is that the camera takes a second picture (for the same time) with the shutter closed and effectively subtracts the "hot" pixels from the final recorded image.
o ISO usually set to 100 since I don't normally care how long the shutter is open for - however, see note later.
o Manual mode so shutter speed and aperture can easily be set.
o set metering mode to matrix
o I use back button focus having set this function on the AE lock button and generally leave the camera in continuous focus but of course a single press of the back button will focus and lock.
o Disable VR on lens (quite normal for any tripod mounted camera).
o Enable remote triggering from the 'I' button - I use the ML-L3 infra red remote so as not to disturb the camera when the picture is taken.
o start with auto focus enabled on lens
I always take night photographs in live view. There are advantages and disadvantages of this. First, live view uses constrast for focussing which is more accurate but slower. Second the mirror is already up so no mirror slap. However, on the D7100 the major disadvantage is you cannot change the aperture whilst in live view (actually you can change the displayed aperture and the aperture the photograph is taken at) but it does not actually change the aperture whilst in live view. More of this later. The other disadvantage is that live view tends to eat batteries so I always carry one or two spare batteries.
Once set up my main process is:
o set appropriate aperture.
o frame picture (this actually can be extremely difficult as often the picture displayed in the LCD is mostly black if there isn't any light sources in view). If this is the case then the view finder is usually better but requires coming out of live view first. On the odd occasion this doesn't work your friend (you remembered to go with a friend) can wield the torch.
o level camera using gyroscope. In live view repeatedly hitting the 'Info' button cycles through views in the LCD, one of which is the gyroscope view. Adjust tripod and/or head to get a level view.
o find an area bright enough in the image to use automatic focus, move the focus square to that area. Press back button to focus and make sure the focus square turns green. If the camera does not acheive focus (focus square turns red) I use two options. The first, and easiest option with a D7100 is to get the torch out and get your friend to point it at the subject whilst you focus. If you can't do this (subject too far away or you forgot to bring a friend/torch) then the second option is to exit live view and open up the aperture wider to get more light in, focus then return aperture to what you wanted. The second option is a pain as it means exiting live view, changing aperture, going back into live view, focussing, and then changing aperature back to what you want. There is also a possibility of focus shift due to changed aperature. Apparently the D7200 does not have this problem and can change aperture in live view.
Some people who are used to taking photographs in daylight are probably now saying why don't you use manual focus and hit the OK button to magnify the image then focus. Have you tried it at night? Firstly when you hit the OK button to magnify the image it takes ages before you actually see something recognisable. Secondly, the image you'll see is so noisy with spots flickering all over the screen that even if you select a brighter spot it is almost impossible to judge when the camera is in focus. If I hit the situation when the camera cannot autofocus even with a torch or opening the aperture wide, I usually resort to setting the focus to infinity and turning it back a little but in general once I get to this situation, I don't hold out much hope of a sharply focussed image.
o turn off auto focus on the lens now as you are focussed. If you don't do this now then a) the camera will attempt to auto focus again when you hit the button on the remote wasting time and batteries and b) the next step moves the focus square to an area appropriate for metering which is probable not the focus point.
o move the focus square to an area in the image you want to use for metering. On the D7100 even in matrix metering the camera will give a small priority to the area under the square.
o make sure (by pressing "info" button) you are in the live view screen which shows the exposure meter. Adjust the shutter speed with the dial to get the exposure meter in the middle. The arrows show you which direction to turn the shutter speed dial.
o I often find that under exposing by one stop works better if there are some areas of bright light somewhere in the frame. I also find it is easier to recover detail from darker areas of a photograph than it is to recover hightlights.
o check histogram and maybe retake picture if incorrectly exposed.
Some side issues:
Landscape photographers are used to taking pictures at small apertures to get the greatest depth of field. Sometimes when you frame your night time photograph you see a similar issue with objects close and some much further away. However, decreasing the aperture lets less light in and makes it harder to focus and slows shutter speed (yes you can increase ISO to compensate). Plus, if you are using a relatively wide angle lens and punch the numbers into a DOF calculator you'll often find the DOF is acceptable at a much wider aperature that allows auto focus or manual focus with magnification. At 16mm or less I often use a larger aperture to enable auto focussing.
A great deal has been talked about wrt banding issues on the D7100 when taking under exposed images or images which are dark and then recovering dark areas. Until I took night time photographs I'd never hit any issues with this. However, I find taking night time photographs I often end up in a situation where I want to recover darker areas by increasing exposure in PP or adding D lighting. I've found that at ISO 100, the so called "banding issue" is worse and at higher ISOs the effect is less obvious. As a result I've experimented with using higher isos than the base ISO 100 and found better results (and less time waiting for the photograph to be taken).
o a find images taken at night need more sharpening and can tolerate more sharpening.
o I generally apply some noise reduction before sharpening especially on skies.
o I use D lighting quite a bit in Capture NX2 but often mask it out of skies where it has a bad effect.