Tuesday, 1 May 2012

NPT: Auto-Focus At Night?

I would like to introduce new section for my blog, it's called Night Photography Trick(NPT).

One of the common challenge that must be encountered by most night photographers is to get subject in focus, shooting at low light condition is not simple as auto-focus won't work most of the time due to lack of contrast in the scene. Getting bright len may help a little but not much, seriously.

Manual focus and Hyperfocal distance are the best friends for night photographer. Night photographer usually relies on them to get subject in focus.

Two widely used techniques are -

1. To get manual focus working, night photographer will illuminate the subject temporarily with torch/flash light(just like using  modeling light), then tune the focus ring until subject in focus. Otherwise switch on auto-focus and get camera to focus quickly if there's enough contrast, then switch back to manual focus once the subject in focus. Using this technique has advantage because you don't have to re-focus again in case want to re-take.

2. Hyperfocal distance is way simpler to operate, just tune the focus ring to infinity, as long as you have your subject in effective focus range/field, you are all good.

The first technique has shortcoming, especially the subject you want to focus is quite far from the camera position and you can't throw enough light on them easily, and this technique is more practical when you have accompany(since you can't move away from your camera when focusing so getting someone to help is a must), second technique is good to get subject in focus, but it also brings greater depth of field and you can't get close distance subject in focus easily(need to do some calculation), you may want to avoid this technique as well when you are shooting below F5.6 aperture setting.

 I have experimented with new technique to get subject in focus at night, one of the problem I want to solve during focusing at night is to focus anywhere I want in the viewfinder, and to get subject in focus as quickly as possible. I normally out for shooting alone at night, and this technique works very well even if you don't have accompany.

The key to this technique is make use of laser pen(laser pointer), I get green laser pen because it works very well in low light condition, read the link here and you will get what I mean. With green laser pen, I can point to the main subject and get my camera auto-focus easily, once the main subject in focus I can quickly switch to manual focus mode to lock down the focus. It also allows me to work quickly when I just want to move my camera slightly for better composition, I can re-focus by pointing the laser to the subject again. Do you want to focus on mid-range subject, no longer you have hard time doing so. The only catch with using laser pen is you must be careful not to point to someone which may cause eye damage.

Grab a green laser pen, it's so small and portable, and experiment with the technique I'm sharing here, then tell me about your experience, the laser pen has become my best friend for the night out for a while now.