Tips & Tutorials

Lens FAQ #3: How are Image Stabilization Stops Determined?

The image stabilization (IS) system is an invaluable tool in hand-held photography, with performance described using terms such as ”equivalent to 3.5 shutter speed stops” or ”4 stop equivalent”. If you’re wondering how the number of shutter speed stops used to denote image stabilization performance is determined, fret no more, as I explain more in this article. (Reported by: Ryosuke Takahashi)

Instruments are used to measure camera movements to reduce fluctuations inherent in human hand movement

IS On

IS Off

EOS 6D/ EF24-105mm f/3.5-5.6 IS STM/ FL: 90mm / manual (f/6.3, 1/30 sec) / ISO 400/ WB: Colour temperature (5200K) / Picture style: Standard

The EF24-105mm f/3.5-5.6 IS STM has an image stabilization performance equivalent to approximately 4 shutter speed stops. Generally, camera shake tends to occur during hand-held photography if the shutter speed isn’t at least 1/focal length. In this example, the shutter speed was 1/30 second with a focal length of 90mm, which was equivalent to slightly less than 2 shutter speed stops. Therefore, the camera shake became quite apparent when IS was turned off. Conversely, by turning on the IS, the shot was taken without camera shake thanks to an image stabilization performance corresponding to approximately 4 stops.

The effective number of stops in the image stabilization system is measured and determined using methods established by the “Camera & Imaging Products Association = CIPA”. (More information on the methods used can be found in the link below.)

http://www.cipa.jp/image-stabilization/index_e.html

Specifically, equipment with image stabilization systems are first mounted onto vibratory apparatus. They are then subjected to two types of wave vibrations that are created mechanically, and then used to shoot a motion blur measurement chart under the same conditions. The results of the shots are then determined using a dedicated blur measurement software, and the effective number of stops indexed.

The image stabilization system performance is not measured using actual hand-held shots so as to prevent any fluctuations that may arise due to differences in the technical skill of the photographer. There is no upper limit to the number of shots that can be taken of the Motion Blur Measurement Chart, but more than 200 shots taken at each shutter speed.

The lowest shutter speed at which the image stabilization system operates is dependent on the camera and the lens, although Canon’s response to this is that their DSLRs “are able to operate at low shutter speeds of up to 30 seconds”. In practice, camera shake is difficult to suppress when shooting with an exposure time of 30 seconds, but the system itself seems to be able to operate even at unexpectedly low shutter speeds. It has to be noted though, that the conditions created by the vibratory apparatus differ from actual camera shake, so the published number of stabilization stops will not completely match what a user experiences when using the camera.

Method for calculating image stabilization performance based on the CIPA standard

A: Image Stabilization performance (Stop)
B: Reference motion blur amount
C: Measured motion blur amount
D: Determination level for image stabilization performance

Diagram obtained from: Figure 4-5-3b Image stabilization performance Calculation Method obtained from “Measurement and Description Method for Image Stabilization Performance of Digital Cameras (Optical System)” published by the Standard of Camera & Imaging Products Association.

In the diagram above, the motion blur amount is shown on the vertical axis, while the horizontal axis shows the shutter speed. The "reference motion blur amount” is the expected value used when calculating the image stabilization performance. The difference between this and the “measured motion blur amount” obtained with the vibratory apparatus is then matched up to the shutter speed on the horizontal axis, and the effective number of shutter speed stops calculated from the “determination level for image stabilization performance”. Furthermore, the measured motion blur amount is determined from the bokeh offset amount and the measured total bokeh amount for the image that was shot. However, this is not done by eye, but is instead measured using dedicated software.

EF lenses with IS image stabilization system performance

Approximately 4 stops

 
 
 

Approximately 3.5 stops

 
 
 
 

Approximately 3 stops

 
 
Ryosuke Takahashi

Born in Aichi in 1960, Takahashi started his freelance career in 1987 after working with an advertising photo studio and a publishing house. Photographing for major magazines, he has travelled to many parts of the world from his bases in Japan and China. Takahashi is a member of the Japan Professional Photographers Society (JPS).

 
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