Thursday, January 04, 2007

Point and shoot at night

No manual setting?!?:

On the way to
A&P tonight I experimented with my Sony DSCP10 (point and shoot) at night. Yes this camera is completely inferior to my 20D and can in no way compete against its smooth high ISOs together with a fast lens at night. However the P10 is not totally useless at night; it just takes a little more effort.

One way communication
One way communication
Left: 1/13, f/2.8, 7.9 mm, ISO 400
Right: 1/4, f/2.8, 7.9 mm, ISO 400

The biggest obstacle is that the P10 lacks full manual settings. So you are left with what the camera thinks is right which usually results in a shutter speed too slow to prevent camera shake. This means you must out smart the camera and fool it into the settings that you want. I should say there is a "P" mode where you can set the ISO (auto,100,200,400), focus (center/multi), and metering (spot/multi) but not the aperture or shutter speed.

Fooling the camera:

In this case I wanted to keep the shutter speed high enough to prevent camera shake but low enough to "properly" expose the frame. To accomplish this on the "P" setting I picked:

a) ISO 400: the photo will be grainy/noisy but it is better to have a sharp noisy photo then a blurry low noise photo;

b) Focus to center AF: the camera will have an easier time focusing in lower light levels with center AF. Although since the focusing is IR, P&S can actually have an easier time focusing then a (D)SLR which use a passive focusing system but I digress...; and

c) Metering to spot: the spot metering allows you get very localized light levels. This will be important for fooling the camera into a particular shutter speed.

The next step is to zoom out to the lens' widest setting and then zoom with your feet to compose the photo. The lens on the P10 has a variable aperture over the zoom range , f/2.8 at 7.9mm to f/5.2 at 23.7mm, so you have the possibility to get more light in
at 7.9mm.

With the above setting I was now ready to attempt a flashless low light photo. First compose your shot, focus, and then check what the camera thinks is the right settings. In the case of the phone booth the camera suggested 1 sec shutter speed with and f-stop of 2.8. There is no way to handhold a 1 sec exposure and not get motion blur. So I focused on parts of the booth with different light levels, locking the exposure settings each time by holding the shutter button half way down, until I got shutter speed of about 1/8. Remember the focal length is 7.9mm so this is inline with the "1/(focal length) rule" to prevent camera shake. Click on the above photo to see notes for the approximate camera settings metered from different regions.


Part of the reason this method works is because the sensor size of a point and shoot (2x crop factor or more) is such that the DOF is more or less infinite. That is everything is in "focus" (reasonably sharp). Have you ever seen point and shoot bokeh? Anyway this allows you to meter one area of the photo and recompose the frame completely, within reason of course, without worrying to much about the focus.


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