Showing posts with label sensor shift. Show all posts
Showing posts with label sensor shift. Show all posts

Friday, 25 December 2009

Image Stabilization

The goal of Image Stabilization (IS) is to be able to take images handheld (or on monopod) at a slower shutter speed than otherwise possible. If the image is too dark, the photographer has the options of increasing the ISO sensitivity, using a larger aperture, or using a slower shutter speed. In some cases, it might be impossible, or undesirable, to increase the ISO sensitivity, or to use a larger aperture. If using a slower shutter speed would normally be impossible due to camera shake, IS might be able to save the picture, stabilizing the image as recorded by the sensor.

At higher sensitivity, the image quality is usually worse, and there are limits to how large the aperture can be on a lens. Large aperture lenses are usually bulky and expensive, and even they have a limited aperture. A large aperture can also be more tricky to focus with, since it will give a narrow depth of field, and the image is usually not the sharpest at the largest aperture. These are some examples of reasons why the photographer might prefer to use a slower shutter speed.

Note that while IS can reduce the effect of camera shake on the sharpness of the image, it does not stabilize whatever you are photographing. If you are photographing moving subjects, you will still need a shutter speed fast enough to freeze the movement, if that is what you want.

The concept of Image Stabilization on consumer cameras was first introduced in the nineties. At that time, most cameras were film based, and the only option for a stabilization technique was through the lens. Later, digital cameras have become the most used, and with this invention another technique for stabilizing the image has arisen: Through shifting the sensor. This could not be done in any efficient way with film based cameras, since the film to be exposed is part of a strip which goes through two spools.

Is is no surprise that the camera systems that have been dominating since before the conversion to digital have retained lens based IS, also called Optical Image Stabilization (OIS). Nikon and Canon both had a number of OIS lenses available before digital photography became common. On the other hand, some systems that have been reinvented for digital have employed sensor based IS, for example Olympus (with the Four Thirds System), Konica-Minolta (later Sony) and Pentax. Some systems, predominantly larger format professional systems, offer no image stabilization at all, e.g., Hasselblad and Leica S2. These systems are mostly intended to be used on tripods, hence IS is hardly needed.

Olympus and Panasonic have taken different approaches to IS. Panasonic have chosen to employ image stabilization through the lens (OIS), denoted with their trademarks "Mega O.I.S." or "Power O.I.S.". Olympus, on the other hand, stabilize the image through sensor shift inside the camera body.

There are advantages and disadvantages with both approaches. The camera body sensor shift technique means that any lens attached can be stabilized. The advantages are obvious: You don't need to pay a premium for OIS lenses, and you can use legacy lenses stabilized. The latter point is very interesting, since Micro Four Thirds cameras, with the short register distance, can use a large number of legacy lenses through adapters.

Lens based OIS, on the other hand, has an advantage with long lenses. The longer the lens, the longer the sensor needs to travel sideways to stabilize the image, in the case of in body OIS. For obvious reasons, there are limits to how far the sensor can travel. With lens based stabilization, lens groups inside the lens shift the path of the light, so that the image is always focused on the sensor. This has an added benefit that the image circle of the lens is used more efficiently.

Even if Olympus and Panasonic have chosen different approaches to IS, you can still use Olympus lenses on Panasonic cameras, and the other way around. But you should not use both image stabilization methods at the same time, if you have a camera/lens combination in which this is possible. This will lead to an over-compensation for camera shake, and will give less sharp images.

Personally, I like the idea of sensor shift IS better than lens based OIS. I think that in camera sensor based IS enables you to use a wide variety of lenses with stabilization, including older legacy lenses. Another benefit is that there is no need for additional stabilizing lens groups in the optical path in the lens. This would be more complicated and costly to produce. The more lens elements the light need to pass through, the more potential for degrading the image quality.

In practice, though, we can see now that the Panasonic Lumix G 14-45mm Mega O.I.S. lens is not significantly more expensive than the Olympus M.Zuiko 14-42mm, even though the Panasonic lens features a stabilizer. Also, the Panasonic lens has generally been found to give better image quality, despite the extra lens elements dedicated to stabilization.

Even though my preference is towards camera based stabilization, I still chose to buy the Panasonic Lumix GH1 and GH2, as I felt that it had more features that I liked. For example, I like the high resolution electronic viewfinder, the tiltable LCD display, the better grip, and the more usable autofocus speed. At the time of buying there was the Olympus E-P1 available, with sensor based IS, however, I felt that it could not compete with the GH1 in the areas mentioned above.