Lens technologies: STM (Stepping Motor)
In June 2012 Canon introduced a new lens motor design to address the issue of lens noise when shooting movies with an EOS DSLR camera. This new lens technology is called STM or Stepping Motor.
Here's what a Stepping Motor is, how it works and the benefits for your photography.
What is a Stepping Motor (STM)?
A stepping motor converts digital pulses into mechanical rotation. One complete rotation of the shaft is divided into a large number of small steps. Each pulse rotates the shaft by one step and the position of the motor shaft can be controlled without any feedback mechanism. A large number of digital pulses give a smooth rotation of the shaft.
There are no contact brushes in the motor, giving the device a long life. The device is reliable, rugged and relatively inexpensive.
A Stepping Motor is designed to be very quiet, making it ideal when the lens is used on an EOS camera to shoot movies, as the built-in microphone is less likely to pick up noise generated by the lens motor.
It also responds faster and switches to a new subject or subject position more smoothly. Whilst this is critical for movies, it's also useful for stills, particularly if your subject is moving around as the autofocus system will be able to track better. You'll notice this most if you're using Live View – the transition to a different subject is seamless.
There are two types of STM in Canon lenses – lead-screw-type and gear-type. The lead-screw-type is super-quick and super-silent, whilst the gear-type is designed for compactness, to work in much smaller lenses. The gear-type does still produce a low level of residual noise, as a result of the gears which are doing the work.
Left: Lead-screw-type STM. Right: Gear-type STM. © Canon
Lead screws (also known as power screws) are the better option and are often used in machinery for precision control of linear movement (as opposed to rotational movement which is more typical in lens drive). They are low maintenance and always very quiet, making them perfect for camera lens application. They are also simple to manufacture, making them an affordable motor option.
In 2016 Canon introduced yet another new lens technology – Nano USM. This offers further improvement in silent lens operation, and has been developed to overcome the difference in needs between video and stills shooting, so offers improvements for both media types.
Lenses which feature STM
EF 24-105mm f3.5-5.6 IS STM
EF 40mm f2.8 STM
EF 50mm f1.8 STM
EF-S 35mm f2.8 Macro IS STM
EF-S 10-18mm f4.5-5.6 IS STM
EF-S 18-55mm f3.5-5.6 IS STM*
EF-S 18-55mm f4-5.6 IS STM
EF-S 18-135mm f3.5-5.6 IS STM
EF-S 55-250mm f4-5.6 IS STM
EF-S 35mm f2.8 Macro IS STM
EF-M 11-22mm f4-5.6 IS STM
EF-M 15-45mm f3.5-6.3 IS STM
EF-M 18-55mm f3.5-5.6 IS STM
EF-M 18-150mm f3.5-6.3 IS STM
EF-M 55-200mm f4-6.3 IS STM
EF-M 22mm f2 STM
EF-M 28mm f3.5 Macro IS STM
Canon Imaging Plaza video excerpt
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