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Author Topic: USM vs. STM Canon Lens  (Read 1620 times)

ahbnyc

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USM vs. STM Canon Lens
« on: September 29, 2015, 11:20:10 pm »

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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MoreOrLess

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Re: USM vs. STM Canon Lens
« Reply #1 on: September 30, 2015, 03:36:27 am »

If I remember correctly the old 55-250mm isnt a USM lens.
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AlterEgo

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Re: USM vs. STM Canon Lens
« Reply #2 on: September 30, 2015, 09:46:42 am »

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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Chris_Brown

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Re: USM vs. STM Canon Lens
« Reply #3 on: September 30, 2015, 10:35:40 am »

From Canon's STM info:
Quote
. . . 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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ahbnyc

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Re: USM vs. STM Canon Lens
« Reply #4 on: September 30, 2015, 11:28:37 pm »

Thanks for the responses -- I must have misread the Canon website the first time when I thought the non-STM model was USM.
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