Image Stabilization: sharp photos in shaky situations

Posted by BenGske on April 14, 2010 in Photography Tips · 0 Comment

In the old days if you needed a sharp photo at slow shutter speeds on dark cloudy days or at night all we had were: tripods, leaning against a wall or buying really fast film. Thanks to technology from years of advancements in military, space and consumer products we now have Image Stabilization (IS) to assist in getting impossible shots and make them insanely sharp. Normally a shutter stop speed as high or higher then the reciprocal of the lens is required to make a sharp photo. For instance a lens with a focal length of 60mm would require 1/60s to produce a sharp image. A 300mm lens would require a shutter speed of 1/300s. Some of the top IS systems today can allow a shutter speed as much as 4-5 stops slower then normal. For example let’s take the 60mm lens with the 1/60s shutter speed. Divide the 60 by say 4 and we have a new minimum shutter speed requirement of only 1/15th of a second. These IS systems literally take the shake out of your photographs by steadying the shot to make it sharp.

The IS systems for SLR’s fall into three main types: 1. Lens mounted 2. Sensor mounted (inside the camera) and 3. Gyro mounted (camera and lens attached to Gyro mount).

1. Lens mounted stabilization has a system of lens elements that float inside of a lens and are attached to vibration and movement correction devices such as coils, springs and dampers that use electromagnets to correct the image so it is stable (see opening photo example of Canon 70-200mm F/2.8 IS L lens IS. There is typically one for vertical movement and one for horizontal. These devices also have gyroscopic (small gyros) sensors attached that feed information to the stabilizer system to correct movements. The gyro is simply a spinning rotor and frame assembly within a Gimbal that let’s the entire assembly rotate in any direction. Once spinning the gyro resists changes in movement and hence the system can reference the difference between the stable gyro and unstable lens and correct any movements. Since the entire system is designed for each size of lens it can be optimized for that lens focal length by being as large as needed. As noted above the longer the focal length of the lens the more stabilization required so the larger the movement required to correct it. And longer focal lengths like 400mm or longer the lens can be as large as required to enclose the IS system allowing corrective movement to be very large. The disadvantage to this systems the requirement to have it in every lens used which can be very expensive.

2. Sensor mounted stabilization moves the IS from out on the lens to the sensor inside the camera. It works the same way as the lens system above but because the sensor inside the camera can only move so much it works best with shorter focal length lenses. The advantage to this type of IS is the fact it will work with all of our lenses to some extent. I say to some extent because once the lens become long enough say 400mm the required movement of the sensor to stabilize the shot is so great that the sensor housing would have to be huge to move enough to stabilize the shots. Hence the advantage of a Lens or external Gyro mounted type IS.

3. External gyro stabilization goes to another extreme by allowing you to have truly huge gyro and stabilization systems allowing for huge amounts of correction to movements and vibration. The camera and lens mount to this type of IS using the tripod mounts on the bottom of the camera or lens. The other advantage of this system is that it will work with any camera and lens made so long as it has a tripod mount. Systems with built in IS will provide even more of a boost by providing additional IS to the stabilization already provided by the external Gyro system. The disadvantages to this type of system are: bulk, size and cost. Disadvantages that are all mute when you need the sharpest possible shot in impossible situations such as mounting a camera system to a helicopter which produces huge amounts of vibration and movement. Systems like these are mainly used by professionals due to the costs and size. Also note that some older IS systems do NOT take into account that they are mounted on a tripod or some other solid object and if left ON will produce blurry photos when the camera and lens are not moving at all. Most newer systems have software algorithms designed to detect the system is tripod mounted and will compensate for vibration in the camera such as shutter and mirror movements. These modern systems can be left ON when tripod mounted. If using and older system be sure to turn OFF the IS when using a tripod. Enough talk, what do images look like with the IS both ON and OFF.

The first photo below with IS OFF was taken at 400mm at 1/50th of a second well below the required reciprocal shutter speed of 1/400th of a second for a sharp photo. As you can see by looking at the birds eyes the photograph is blurred both in the vertical axis and some in the horizontal axis. The second photo with IS ON was taken at 400mm at 1/40th of a second is even lower below the required shutter speed but is very sharp thanks to the wonders of IS. Pushing your IS to the extreme: Think that you can only pull off a shot that’s 4-5 times slower then the reciprocal of the focal length? Think again. By using the tips below I have been able to take sharp shots at 400mm with a shutter speed as slow as 1/20th second. Put your camera in the highest continuous shutter mode so that when you press the shutter button it takes as many photos as fast as possible. Brace your and support your elbows against a solid object if possible or against your side if not. Time your breathing so that you are close to maximum inhale or exhale and press and hold the shutter button until you take at least 4 or 5 photos in rapid succession and then let the shutter button go. Try to be as smooth as possible and practice this until you are as smooth as possible. When you review your photos later chances are the second or third photo in your group will be sharp even at extremely slow shutter speeds and well below the reciprocal focal length. With this technique I have been able to squeeze sharp photos as slow as 1/20 a second out of a 400mm focal length even with an older style IS only designed to give a 2 – 3 stop advantage. Conclusion, when used correctly an IS system will help you pull off that impossible shot and is an indispensable tool for the modern photographer.