Update 8-22-13: Canon has a new version of the 55-250 (budget zoom) that uses STM technology.  This brings the number of STM equipped lenses to four. The 18-55 IS STM, The 18-135 IS STM, The 40mm STM and now the 55-250 IS STM.     Trying to decide if you should buy the T5i with 18-55 or 18-135? Watch my 18-55 IS STM vs 18-135 IS STM Discussion.    If you need help deciding which prime lens you should buy.   Best Value Canon Prime Lenses.

I have a video demonstrating the difference in focusing, during video when using one of the new STM lenses versus USM but was recently asked how they compare when using phase detection.  The focusing method used when looking through the viewfinder, not the LCD.     In the Canon T4i when you focus through the viewfinder you use what I call the big brains of the camera and the focusing method used is called Phase Detection.  So how does the two new STM lenses compare with a USM

Real Quick Definitions

STM: Stepping Motor Technology, Canon claims that this technology allows smooth and silent autofocus perfect for video

USM: Ultra Sonic Motor Technology, Canon claims fast and silent autofocus and most USM lenses allow full-time manual focus

FT-M: Full Time Manual Focus means that you can adjust the focus manually, by turning the focus ring on the barrel of the lens, when the focus switch, also on the lens is set to AF or MF.  Lenses that do not allow FT-M must be physically switched to MF before you can manually focus.

The Canon 40mm f/2.8 STM and the 18 – 135 f/3.5 – 5.6 STM IS all for full time manual focus override. It does require a half-press of the shutter button. 


Brief Review of the 18-135 STM 

The new 18 – 135 STM lens is fast and silent (actually I already knew that from my full review – Full review of 18 -135 STM Lens) and have now confirmed that it is amazingly silent when it focuses. The 40 f/2.4 STM lens makes a bit more noise but still pretty quiet and fast to focus, maybe not quite as fast as the 50 f/1.4 USM but nearly so.    The more I shoot with the 18 – 135 STM lens the more impressed I am and it really compliments the Canon T4i/T5i.   The newer 18-55 IS STM is equally silent.


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 Box Canyon Tunnel on the descent from Paradise, Mt Ranier National Park Captured with the #GH5 and 12-35 f/2.8
 My niece giving me that look. From early morning family adventures in Saguaro National Park, Arizona
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