Luminous Landscape Forum
Equipment & Techniques => Cameras, Lenses and Shooting gear => Topic started by: ahbnyc on September 29, 2015, 11:20:10 pm
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I am thinking of buying the Canon 55-250 EF-S lens, but it comes in both an STM and a USM model. What is the practical difference between the two? Also, for a camera with an APS-C sensor is the alternative of the 70-300 USM IS EF lens worth the extra $400 cost (and added weight)? Thanks.
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If I remember correctly the old 55-250mm isnt a USM lens.
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I am thinking of buying the Canon 55-250 EF-S lens, but it comes in both an STM and a USM model. What is the practical difference between the two? Also, for a camera with an APS-C sensor is the alternative of the 70-300 USM IS EF lens worth the extra $400 cost (and added weight)? Thanks.
stm is a linear stepper motor model that works fine with CDAF (=dSLM, they are optimized to execute a series of fast small/fine moves, hunting for a contrast maximum), USM motorized lens needs PDAF or PDAF on sensor for a good work (they are optimized to execute a fast move to a certain focusing position on a single command from camera and may be one more move if PDAF is setup up to double check... they are not very good for CDAF contrast hunting)
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From Canon's STM info (http://www.usa.canon.com/cusa/consumer/standard_display/Lens_Advantage_Perf#usm):
. . . a stepping motor (STM) drive, designed to deliver smooth and quiet continuous AF during video shooting when paired with the Movie Servo AF feature on select EOS cameras.
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Thanks for the responses -- I must have misread the Canon website the first time when I thought the non-STM model was USM.