RF STM or USM

[g_khajanchi]

Which lens is best in terms of cost and quality RF STM or USM.

[shadowsports]

Greetings,

There's no hard fast rule or single answer for this. The motor used depends on a few factors.  Cost, performance and weight are examples.  

In general, STM lenses are used in lenses which are shorter FL.  They don't always have the power or speed to drive lenses with longer FL and heavier lens objectives.  They are popular with people who shoot video.  They are very quiet.

I don't follow motor technology too closely, but I believe there are three types of USM motors.  USM motors are used in lenses with heavier lens objectives to maintain performance.  This is not true in every case.  

[deebatman316]

Canon has been through multiple AF motors over the years. Some of which have been retired and replaced by newer faster motors.

• Arc Form Drive (originally named "Autofocus Drive") (1987-1992, original EOS AF motor, retired)
• Ring Type USM (1987-Present, original USM AF Motor) 
• Micro Motor (1993-2012, retired)
• Micro Motor USM (1992-2008, retired)
• STM Stepper Motor (2012-Present)
• Nano USM (2016-Present)