Difference between USM and STM lenses

[JFG]

Now I am really challenged and confused ! : )

So, here I'm saving my poker winnings for my next RF lense, which would either be an RF 14-35mm f4  L IS USM now $1,199.00 or the RF 15-35mm f2.8 L IS USM now $2,099.00.  To complicate matters, Canon now introduced the RF 10-20mm f4 L IS STM now $2,299.00..  One question that I have is :  What is the difference between an L IS USM lens and an L IS STM lens ?  I thought that a L USM lens is better quality than an L STM lens.  Canon has set the price of $2,299.00 on the RF 10-20 f4 L IS  STM which kind of throws me, cause I thought that IS L USM lenses are higher quality and therefore more expensive.   Is it that Canon mislabeled their new lens or am I wrong in my assumption  ? (BTW, the cost for me is not an issue)..  Please clarify the aforementioned for me ...  Your responses will be greatly appreciated. 

[deebatman316 · Accepted solution]

This lens has smaller lens elements than other lenses. To keep size down an STM AF motor was used since the lens is light and has small lens elements. Larger lenses require Ring Type USM due to the lens' elements being larger. An STM AF would result in slow AF when trying to move those large lens elements around. Canon has used 3 types of USM AF motors. Those are Ring Type USM, Micro Motor USM & Nano USM. Micro Motor USM was designed to be cheaper. These lenses DO NOT support full time manual focus. They lack a focus distance scale and spin the focus ring when AF is being used. EXCEPT the EF 50mm F/1.4 USM lens. This lens uses Micro Motor USM but has an additional clutch system to allow full time manual focus. This lens also has a focus distance scale window. Ring Type USM was introduced in 1987 with the EF 300mm F/2.8L USM lens. ALL early Ring Type USM lenses were focus by wire lenses just like STM lenses are. To keep costs down Canon implemented a mechanical clutch override system. To allow for full time manual focus. Nano USM allows full time manual focus the same way an STM lens does. The first Nano USM lens was the EF 70-300mm F/4-5.6 IS II USM lens which was released in 2016. Not all of Canon's L lenses use Ring Type USM AF motors. All early EF Mount lenses used Arc Form Drive (1987-1992) then later Micro Motor from (1993-2012). In 2012 STM would replace Micro Motor the first lens to use an STM AF motor was the EF-S 18-135mm F/3.5-5.6 IS STM lens. Arc Form Drive (AFD) lenses have a 3-4 FPS limit in AI Servo. This is due to how AF & aperture control take place compared to a USM (all types), Micro Motor & STM lenses. Arc Form Drive (AFD) lenses sequentially focus then stop down the lens. USM (all types), Micro Motor & STM lenses simultaneously AF & stop down the lens. In fact Canon's first 3 "L" the EF 100-300mm F/5.6L, EF 20-35mm F/2.8L & EF 80-200mm F/2.8L ALL lack Ring Type USM AF motors despite being "L" lenses.

• Ring Type USM (1987-Present)
• Micro Motor USM (Discontinued 1993-2016)
• Nano USM (2016-Present replaced Micro Motor USM)

[deebatman316 · Accepted solution]

Canon is still using Ring Type USM in lenses today. In fact the RF 85mm F/1.2L USM lens uses a Ring Type USM AF motor. Canon hasn't stopped production of Ring Type USM AF motor lenses. Nano USM combines the speed of Ring Type USM and the quietness of STM AF motors. So the current 2 USM AF motors are Nano USM & Ring Type USM. Ring Type USM was originally designed for fast AF. It was NOT originally intended for video work. Ring Type USM lenses released prior to 2009 don't support DPAF (Dual Pixel Auto Focus). They often "snap" back to acquire focus and the aperture jumps from setting to setting. Ring Type USM lenses released from 2009 and later don't suffer from these problems anymore. They transition smoothly when acquiring focus and transition between different apertures smoothly. Instead of causing "jumps" in exposure while recording. Micro Motor USM lenses never got upgraded like this. Instead Canon replaced it with Nano USM. But Canon had discontinued Micro Motor USM lenses years before Nano USM was released. 

[Waddizzle]

I don’t think it is a typo.  If it were, then it should have been corrected by now.

This would be the first L series lens that I have seen with STM motors.  The EF-S mount STM zoom lens were almost expressly designed with using Movie Servo AF in video modes.  The EF mount USM lenses were not as smooth and silent as the STM zooms.

Am I saying this lens is similarly designed with Movie Servo AF in mind?  No, but I suspect that it is likely that it was designed with video modes in mind.

[JFG]

So if the EF mount STM lenses are smoother and quieter than the EF mount USM lenses, does that hold true for the RF mount lenses ?  If so, than why does canon equip the lower priced RF lenses with STM motors which are smoother and quieter than the USM motors.  I know that the L lenses are higher quality all around..  It's a bit confusing to me.

[deebatman316 · Accepted solution]

This lens has smaller lens elements than other lenses. To keep size down an STM AF motor was used since the lens is light and has small lens elements. Larger lenses require Ring Type USM due to the lens' elements being larger. An STM AF would result in slow AF when trying to move those large lens elements around. Canon has used 3 types of USM AF motors. Those are Ring Type USM, Micro Motor USM & Nano USM. Micro Motor USM was designed to be cheaper. These lenses DO NOT support full time manual focus. They lack a focus distance scale and spin the focus ring when AF is being used. EXCEPT the EF 50mm F/1.4 USM lens. This lens uses Micro Motor USM but has an additional clutch system to allow full time manual focus. This lens also has a focus distance scale window. Ring Type USM was introduced in 1987 with the EF 300mm F/2.8L USM lens. ALL early Ring Type USM lenses were focus by wire lenses just like STM lenses are. To keep costs down Canon implemented a mechanical clutch override system. To allow for full time manual focus. Nano USM allows full time manual focus the same way an STM lens does. The first Nano USM lens was the EF 70-300mm F/4-5.6 IS II USM lens which was released in 2016. Not all of Canon's L lenses use Ring Type USM AF motors. All early EF Mount lenses used Arc Form Drive (1987-1992) then later Micro Motor from (1993-2012). In 2012 STM would replace Micro Motor the first lens to use an STM AF motor was the EF-S 18-135mm F/3.5-5.6 IS STM lens. Arc Form Drive (AFD) lenses have a 3-4 FPS limit in AI Servo. This is due to how AF & aperture control take place compared to a USM (all types), Micro Motor & STM lenses. Arc Form Drive (AFD) lenses sequentially focus then stop down the lens. USM (all types), Micro Motor & STM lenses simultaneously AF & stop down the lens. In fact Canon's first 3 "L" the EF 100-300mm F/5.6L, EF 20-35mm F/2.8L & EF 80-200mm F/2.8L ALL lack Ring Type USM AF motors despite being "L" lenses.

• Ring Type USM (1987-Present)
• Micro Motor USM (Discontinued 1993-2016)
• Nano USM (2016-Present replaced Micro Motor USM)

[JFG]

Great explanation, deebatman316 !  I now understand the difference between the STM and USM AF motors.  Good of you to post the time line of when Canon used the different USM types.  Good to know that all of my R6 Mark II lenses are RF L Nano USM..  The STM motors can handle smaller lighter lenses with smaller elements.   That's why all of my M50 Mark II lenses are STM AF as they are smaller and lighter.   Nano USM AF are used with the larger lenses with larger elements or the AF would be to slow..  Great job explaining USM vs STM !

[deebatman316 · Accepted solution]

Canon is still using Ring Type USM in lenses today. In fact the RF 85mm F/1.2L USM lens uses a Ring Type USM AF motor. Canon hasn't stopped production of Ring Type USM AF motor lenses. Nano USM combines the speed of Ring Type USM and the quietness of STM AF motors. So the current 2 USM AF motors are Nano USM & Ring Type USM. Ring Type USM was originally designed for fast AF. It was NOT originally intended for video work. Ring Type USM lenses released prior to 2009 don't support DPAF (Dual Pixel Auto Focus). They often "snap" back to acquire focus and the aperture jumps from setting to setting. Ring Type USM lenses released from 2009 and later don't suffer from these problems anymore. They transition smoothly when acquiring focus and transition between different apertures smoothly. Instead of causing "jumps" in exposure while recording. Micro Motor USM lenses never got upgraded like this. Instead Canon replaced it with Nano USM. But Canon had discontinued Micro Motor USM lenses years before Nano USM was released. 

[JFG]

Hi deebatman316, for my R6 Mark II, I have the RF 70-200mm F4L IS USM with Nano USM focusing + Nano USM floating and also have an RF 24-105mm F4 L IS USM AF with full time manual.   What type of USM AF does the RF 24-105 F4 L IS USM use ?  I got the lense with the R6 Mark II camera on 11-17-2022..  In the unit specs it only says " Focus Adjustment  :  AF with-full time manual" ..

[deebatman316 · Accepted solution]

The RF 24-105mm F/4L IS USM lens uses Nano USM. All RF mount lenses use electronic focus rings. They use what is called "focus by wire". The camera must be powered up for the focus ring to work.

[JFG]

Thanks Demetrius, you're the man !   👍