Lens advice USM vs STM

[bevvet]

Hey, so I just recently upgraded to a Rebel T8i after using a T3i for years, and I’ve been using the same lenses (EFS 18-55mm and EF 70-300) for the new one. I’m currently in school majoring in photography and to make money on the side I do professional shoots here and there, and I’ve found that having to shift between the two lenses has been extremely cumbersome, so I’ve made the decision to buy a used 18-135mm EF lens.

However, i can’t decide if I should get the USM or the STM. From what I understand, it’s just the auto-focus system, but I can’t see any real difference between the two from what I’ve tried to find. Does it even matter? I primarily shoot portraits and cinematography on occasion, if that helps.

[Tronhard]

Hi and welcome!

I have had both versions and I would agree that optically-speaking, there is little difference between the two.  It's more about the focusing system.  Both are fly-by-wire and so one can leave the lens on AF and still manually focus, which is excellent.  The USM one is faster to focus (a bit), and is particularly suitable for video work - it even has contacts for its own optional focusing motor.  I prefer the cosmetic feel of the USM version and it is quite a few years newer technology than the STM version, but probably more significant for you will be how much you have to spend for either.  

A good indicator of the quality of an optic is how it takes a crop, and the following pair was shot with the USM version:  All images shot hand-held, available light
80D, EF-S 18-135 USM@135mm, f/5.6, 1/200sec, ISO-2000  Cropped version of previous shot

This one was taken with the older STM version of a Māori dance group in brutal midday sun.60D, EF-S 18-135STM@79mm, f/7.1, 1/400sec, ISO-200

[ebiggs1]

Personally I would buy the USM if I could but like Trevor says it probably doesn't make a huge difference. You said you are looking used so I imagine money is of most importance. But you also said making money from professional photos. The lens is the big dog. It is not the camera. I would rather have a Rebel T8i and a top level Canon L lens than an R1 with a bottom tier lens. Yes, I know you need to start slow but keep what I just said in mind as I have done that for five decades and longer.

[stevet1]

bevvet,

I also have the T8i. I would agree with my esteemed colleagues Trevor and ebiggs.

I was lucky enough to be gifted the 18-135 USM lens and it stays on my camera 90% of the time.

Steve Thomas

[normadel]

If the 18-135 STM is like the 18-55 STMs, you cannot even focus manually if the camera is turned off, because there's no mechanical connection between the focusing ring and the focus mechanism. That's what "fly-by-wire" means. The USM CAN be focused manually without power, because it's mechanical from focus ring to mechanism. 

If that matters to you.

[Tronhard]

OK, I get your point, but now why one would want to focus with the camera turned off, considering it needs power to actually take a photo.   Is that something you do for a specific reason?

One area that some folks have suggested is a potential issue with STM or nano-USM is if using extension tubes without contacts - in which case the lens will not manually focus.   I have very cheap, plastic extension tubes, but they do have contacts, so I decided to take a shot of my 42YO classic Arnie watch face, with my 80D.  It was just sitting on the table with the watch facing it and not necessarily parallel to the camera.
Manual Focus, with a 31mm extension tube - shows a bit of dust from a cloth I dropped around to reduce reflections!
80D, EF-S 18-135 USM@116mm, f/9 0.5sec, ISO-2500
 

[normadel]

Yes, I at times do it for a specific reason. That's me. Like I said, "If that matters to you." 

[Tronhard]

My comment wasn't meant to be critical, but curious - I hoped to learn something that I was unaware of.  But, whatever... 🙂