Its not easy at all and rarely produces nice images, but there are ways to improve your odds of coming back with a some decent images. Shooting while in motion is difficult because it requires a very short reaction time from both the photographer and the camera. One good strategy to avoid any problems is not to shoot from a moving vehicle and have the driver stop each time a photo opportunity appears.
That is my usual strategy: if the vehicle is in motion put the camera away and enjoy the ride. It can be much more frustrating to keep trying to get a good shot than not to shoot and absorb the scenery mentally. Recently, on a long and scenic drive as a passenger, I decided to actually try anyways. A few decent images even camera back, although they were far in between.
Here is how to improve the odds of getting some good shots from a moving vehicle:
- Cut down focusing time: Most cameras take pictures much faster when they do not have to focus. Among compact cameras, there is often a way to simply set the focus distance to infinity or to the hyperfocal distance of the lens. Casio calls the latter pan-focus, others sometimes make it part of a particular scene-mode. With a DSLR, switch it to manual focus (MF) mode and rotate the focus-ring until the infinity position. Care must be taken here because some lenses change the focus distance while being zoomed, while others allow focusing past-infinity which means that the focus ring cannot simply be turned all the way. It would be really nice if lenses had an infinity-focus-lock for such occasions.
- Aim far: The further things are, the less they move relative to the camera position. This helps with framing shots and making sure that subjects remain in focus. At the same time, use a small aperture to increase depth-of-field.
- Go wider: Since precise framing while in motion is hard, give yourself some cropping room by using a slightly wider focal length than needed.
- Cut down thinking time: During the fraction of second when the desired subject fits in the viewfinder, it is not time to fiddle with the camera. For that, use a semi-automatic or fully-automatic mode with a metering mode which takes into account the entire scene. Multi-segment, center-weighed and average metering are all good for that. If the amount of sky varies greatly during motion, use exposure bracketing in half-stops.
- Let the camera know what you need: Fully automatic modes like Program or Auto mode rarely choose the optimal exposure parameters for photography from a moving vehicle. It is possible to use program-shift but that takes time. A sharp image requires a shutter-speed fast enough to freeze the motion of vehicle. Small apertures greatly help with keeping subjects in focus, but too small apertures require slower shutter-speeds. If your camera is a Pentax K10D, the TAv mode is fantastic: set the shutter-speed to a reasonably fast speed (say 1/1000s or faster) and the aperture to something with a good depth of field (say F6.7 or F8), the camera will choose the appropriate ISO. Otherwise, you use aperture-priority mode with as high an ISO as you consider acceptable. That will make the camera choose the fasted shutter-speed which produces a properly exposed image. For cameras without manual controls, use the sports or action scene-mode.
- Try again, automatically: Continuous drive and bracketing give you more pictures from which to choose the acceptable ones. Use continuous drive when the lighting situation changes slowly, exposure bracketing otherwise. Usually, 1/2 stop increments are best.
- Get a good seat: Place yourself next to a window, so that you can open it. If it does not open, make sure both sides are clear before departing and use a polarizer to avoid seeing your reflection while taking pictures. Try to avoid the side of the vehicle which faces the sun. It creates scenes of very high contrast which can be impossible to expose properly. If facing the sun, try to minimize the amount of sky in the viewfinder.
- Do not be the driver: Obviously. When an interesting subject approaches, ask the driver to slow down, particularly on bumpy roads. Keep the camera in the vehicle and use an appropriate neck or shoulder strap.