Image stabilization in a wider sense simply refers to the methods or techniques applied to still the camera during shooting for sharper images—including the use of a tripod.
Optical Image stabilization (hereafter, “IS”) is the technology used by manufacturers to steady the image when shooting hand-held. Typically, it is only useful for a range of shutter speeds. IS will not make any difference shooting at 1/500th—this is already a short enough time period such that minimal camera movement (hand movement) will have almost no impact at all of the final image sharpness. Equally, shutter speeds counted in seconds (e.g. night photography) will require a tripod regardless.
IS is useful, however, for shutter speeds between (say) ½ a second and 1/60th where IS can make the difference between a keeper and a photograph that goes straight into your desktop recycle bin. We are talking about percentages here. At 1/30th you might end up with one acceptably sharp image in every five shots. Move to 1/60th maybe this goes up closer to 50%.
The main benefit is noise reduction—and thus a higher quality image. Nikon, for instance, claims that it’s Vibration Reduction (VR) technology (just Nikon’s name for Image Stabilization) can give an improvement of four-stops versus shooting without. What this means is that say you had a standard set-up (no IS, hand-held) and the following settings gave a correct exposure:
ISO 3200, 1/250th, ƒ/5.6
You don’t want to change the aperture—because that gives the depth of field you want and you’ve already pushed the ISO up to 3200 to give you a shutter speed which isn’t going result in camera shake blur. With 4-stops of IS you could change the settings to:
ISO 200, 1/30th, ƒ/5.6
… and end up with a photograph that is just as sharp but with a less noise (ISO 200 vs 3200).
Obviously, image stabilization is only there to help solve camera shake—it does not help if you’re shooting a fast moving scene.
How does it work?
Optical image stabilization is split into two main technologies: lens based and sensor based. Canon and Nikon opt for lens based systems whereas something like the Olympus PEN series is sensor (or “in-camera”) based.
Lens image stabilization
In lens-based image stabilization an additional lens is placed within the lens case that is able to move 360° in a perpendicular direction relative to the optical axis. Two sensors within the unit are they used to detect horizontal and vertical movements and a small motor makes micro-adjustments in the opposite direction to counter-balance. As such, it can compensate for left/right and up/down directional movements but rotational movements (i.e. twisting the camera) will still impact on the image.
Some Canon lenses have two modes for IS—one standard and one that directs is there is constant movement in a given direction for a sustained period of time (i.e. when panning the camera for example to follow a sports car in motion) and shuts off the IS in that direction. Similarly, Nikon offers an “active” mode that is designed to further increase the floating lens movement for when you are shooting from an unstable platform (e.g. moving car, boat).
- Better performance as each image stabilization system is designed specifically for the lens in which it’s housed.
- Image is stabilized in the viewfinder as well
- Better with longer focal length lenses which typically require larger corrective movements (and sensor movement is more restricted than in-lens)
- Better AF performance (again, the image is stabilized before it reaches the AF unit). This is less of an issue with cameras that use on-sensor focusing methods but might be for DSLRs using a phase detection method.
- More expensive (you’re effectively paying for a new IS system with each lens)
- Not really suitable for smaller mirrorless cameras where compactness is a selling point and IS systems built into pancake camera lenses are not viable.
Sensor image stabilization
Also, referred to as “mechanical image stabilization” this technique involves making the counter-balancing movements on the sensor itself rather than an additional lens element. The obviously advantage here is that you have image stabilization regardless of what lens you fix to the camera body.
- Cheaper in the long-term (you need only pay for one IS system)
- Compatible with any lens (in a lens-based system if the lens doesn’t come with IS then you’ll just have to make do without)
- The opposite of the lens-based pros, but in a nutshell: performance vs a lens-based system.