Image Stabilisation

Posted by: Fast Air Photography Tags: Image Stabilisation Posted date: January 22, 2012 | No comment

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Image Stabilisation is known by a number of names depending on the manufacturer. I’ve used both Canon’s Image Stabilisation and Nikon’s Vibration Reduction systems. For this article I’ll use the term ‘image stabilisation’ or ‘IS’ as a generic phrase rather than a reference to any particular system.

The big question about image stabilisation is always should I use it? I’ll attempt to answer that question here for aviation photography. The answer may well differ for other types of photography.

To start with let’s look at what IS was designed to do and how it works.

What Is Image Stabilisation Designed To Do?

Image Stabilisation is designed to eliminate, or at least reduce, what is called ‘camera shake’. This is the name given to the small movements of the lens whilst taking a photo. This shouldn’t be confused with ‘motion blur’ where the blurred image is caused by the autofocus not tracking the subject, a shutter speed too low to capture the subject, incorrect panning technique or other large movements of the lens.

‘Camera shake’ is cause by the slight movement of the photographer’s hands. The average person’s hands move slightly up to five times a second. These small movements are magnified by the focal length of the lens used, so for larger (and usually heavier) lenses the problem becomes more pronounced.

A rule of thumb used by most photographers is to keep the shutter speed greater than one over the focal length to avoid ‘camera shake’. For example, if you had a 400mm focal length lens you should be aiming to shoot 1/400s or quicker without the help of either something to support the lens such as a tripod or an image stabilisation system.

How Image Stabilisation Works?

Canon and Nikon’s image stabilisation systems are both lens based and work using two sensors that direct movement on the horizontal and vertical axis. When movement is detected the IS system can move lens elements to redirect the light path and in effect cancel out that movement.

Early versions of the system were capable of 2 stops of stabilisation and later ones are capable of 5 stops of stabilisation.

Image Stabilisation from Canon

Mode 1 – movements on both the horizontal and vertical axis are cancelled out. You are unable to pan with this mode.

Mode 2 – movement is detected on a particular axis and the opposing axis has IS applied to it. This allows panning. This is monitored in case the movement of the lens is swapped from one axis to the other. If it does change them IS will be applied to the other axis. If the movement is diagonally neither axis has IS applied to it.

Vibration Reduction from Nikon

Normal mode – works in the same way as Mode 2 from Canon.

Active mode – works in the same way as Mode 2 from Canon but allows larger movements before applying stabalisation.

Should I Use Image Stabilisation?

I don’t believe this can be answered with either a simple yes or no. Having IS on a lens doesn’t mean you should decide to switch it on or off and then leave it. There are times when having it on can help and times when it doesn’t. Once you understand what IS does and how it works you can decide yourself when to turn it on and when to turn it off. My personal experience is below.

I start with IS switched off and it remains off until I feel it the feature will benefit me. I have decided to start with off as my default setting as the majority of my time is spent shooting fast jets with a shutter speed that is always higher than the focal lengths I’m using. If you remember the rule of thumb I talked about earlier this means camera shake shouldn’t affect these photos. Turning on IS in this situation offers me no benefit and there is the potential it might actually introduce a couple of problems instead.

The first is with autofocus. Before autofocus can be started on a lens with IS enabled the lens has to be stabilised. This pause before autofocus can start could cost you a picture if something unexpected happens and you didn’t have time for IS to start up. Once autofocus is up and running the tracking speed of the autofocus system is as fast as with IS off.

The second is relying on the IS system keeping up with the erratic movements of a fast jet. With rapid changes of direction the IS system has to keep up and make sure it applies the stabilisation to the correct axis or neither axis if the movement is diagonal. To be fair I’ve only ever experience the situation once where I’ve felt resistance against my movement as IS was applied to the incorrect axis but even if it keeps up it this scenario small involuntary movements of your hands is going to make very little difference as you aren’t holding the lens still or moving in one direction for any length of time.

Neither of these are big problems and the potential for them to impact you isn’t that great but why accept them when the system isn’t going to give you any advantages?

I find IS works well if you making movements in one axis at low shutter speeds. Shooting a fast jet side on as it goes don’t a runway with a low shutter speed to give a sensor speed would benefit from using IS. Shooting hovering helicopters is also a good time to make use of it to get a decent amount of rotor blur in the shot. If both these situations small involuntary movements of my hands could impact the photo so I do consider using IS.