topic Re: STM vs USM L glass difference in EF & RF Lenses

STM vs USM L glass difference

EK25 — Mon, 25 Aug 2025 20:04:58 GMT

Please can we talk about how huge the actual difference between STM vs L USM lenses is... I am looking at 50 mm RF lenses and the $2000 price difference is killing me. I understand that different AF systems, sound vs no sound for videos. I am NOT a sports photographer (the fastest moving objects I am shooting are running kids). So if I took 2 images seconds apart, same settings and camera, with a STM vs USM lens what the actual difference between them will be? Sharpness? Bokeh pattern + background separation? What else??? Thank you in advance!

Re: STM vs USM L glass difference

kvbarkley — Mon, 25 Aug 2025 20:36:38 GMT

You are leaving a lot out by just talking about "L", the other key difference is maximum aperture. The lower the f/number the larger the amount of distortion free glass required:

https://kenrockwell.com/canon/eos-r/lenses/50mm-f12.htm

but that said, if you took two images in plenty of light at moderate (f/8) apertures and shutter speeds, you might be hard pressed to see the difference. As the Online Photographer says, almost any camera can take good pictures under "average" conditions.

Re: STM vs USM L glass difference

ebiggs1 — Tue, 26 Aug 2025 14:03:10 GMT

"... what the actual difference between them will be?"

80% to 90% of the time for GP photos, no difference. None anyway that will make much difference to you.

Re: STM vs USM L glass difference

EK25 — Tue, 26 Aug 2025 14:20:15 GMT

Thank you. May I please ask in what situations there will be notable differences then? I am shooting families as a business, and I still want the best for my clients.

Re: STM vs USM L glass difference

EK25 — Tue, 26 Aug 2025 14:20:37 GMT

Thank you so much, this is helpful!

Re: STM vs USM L glass difference

kvbarkley — Tue, 26 Aug 2025 14:26:49 GMT

Generally widest aperture either because of low light or required narrow depth of field.

Note that performance is relative to maximum aperture. A f/1.2 lens will perform better at f/1.8 than a f/1.8 lens. And an L lens will probably always outperform a non L lens

Re: STM vs USM L glass difference

FloridaDrafter — Tue, 26 Aug 2025 17:36:18 GMT

@EK25 wrote:

Thank you. May I please ask in what situations there will be notable differences then? I am shooting families as a business, and I still want the best for my clients.

I have both the RF 50mm f/1.8 STM and the RF 50mm f/1.2L USM. I use the 1.2 on my R5's (I & II) and my wife uses the 1.8 on her R6 II because she needs a light rig (she is disabled). As EB pointed out, for general shooting the 1.8 works OK. Keep in mind that just about any shot can be brought to life in post using PS or DPP.

The 1.2 is by far the sharper lens SOOC so if you shoot JPeG, there is less processing that needs to be done in camera or in post. Canon can make these consumer lenses, like the RF 1.8 STM, at a more affordable price by using fewer or no corrective glass or elements in the lens itself, so they depend on in camera lens correction (LC). As mentioned, this is no big deal if you shoot RAW and do post editing OR don't mind burdening your camera with that task, but you will still have to spend more time in post with a consumer lens like the f/1.8. In certain situations, in camera LC can slow you down or reduce the number of shots you can take when using "burst" mode, but once again, this may not be an issue for you.

As mentioned by kvbarkley, low light situations is where you would use either the 1.8 or 1.2 at their widest aperture. But the 1.2 is such a sharp lens that it really doesn't matter. So far, all of the RF L lenses I've used (5) are sharp at their widest aperture. You can't, or at least I can't, say this about consumer lenses, either EF or RF. I will just mention that the 1.2 gives you a better base starting point and stays sharp to the corners through all apertures.

RF 50mm f/1.2L USM on the EOS R5, 1/200th, f/16, ISO 1600.

RF 50mm f/1.2L USM on the EOS R5, 1/1250th, f/16, ISO 1000.

RF 50mm f/1.2L USM on the EOS R5, 1/1250th, f/1.8, ISO 1000.

RF 50mm f/1.2L USM on the EOS R5 mark II, 1/60th, f/1.2, ISO 5000. This is lightning behind a cloud.

RF 50mm f/1.2L USM on the EOS R5 mark II, 1/1250th, f/1.2, ISO 1250. My son-in-law took this of my daughter while they were visiting. We were just messing around and he had never used a Canon MILC before. Lighting was with just one of my 10" LED light panels.

Be forewarned that the 50mm f/1.2 or any f/1.2 lens for that matter, can be a cruel mistress, particularly using f/1.2 at close distances because of the very narrow DOF.

Newton

Re: STM vs USM L glass difference

deebatman316 — Tue, 26 Aug 2025 18:33:33 GMT

This isn’t so much about AF motor type as there are some L lenses that use STM, VCM, Ring Type or Nano USM. L lenses will always be optically better than their consumer grade counterparts. L has nothing to do with the AF motor a lens uses. The RF 10-20mm F/4L IS STM is an L lens with an STM AF motor. Also not all consumer lenses use STM AF motors. The RF 24-240mm F/4-6.3 IS USM is a consumer grade lens with a Nano USM AF motor. Early EF Mount L lenses didn’t use USM AF motors. Instead they used Arc Form Drive AF motors which are very slow. But were better than Micro Motor which replaced Arc Form Drive. In fact no L lens from Canon ever used Micro Motor or Micro USM. They always used better and faster AF motors.

Re: STM vs USM L glass difference

ebiggs1 — Wed, 27 Aug 2025 15:28:07 GMT

" May I please ask in what situations there will be notable differences then?"

Yes, of course, here's the deal. "80% to 90% of the time for GP photos, no difference." For the average person who just wants a nice digital camera and nice photos for GP (general purpose) like sharing with family, friends and perhaps u/l to social media 9 times out of 10 there is no noticeable gain from "L" lenses. The let's say the 'better' lens come from folks that are in the photography business or who are photography enthusiasts and want every last bit of IQ that's possible. And, truthfully, sometimes the only improvement is in the build quality of the "L" lens not the IQ. Keep in mind you are In a world where an iPhone photo is considered good. And for the average person it is.

Some guys, perhaps the folks above, are pixel peepers and look for every last bit of IQ. Some guys fret over how fast the AF is but again they are enthusiasts or advanced hobbyists. Again for most of us the AF of any lens is just fine and matter of fact a couple "L" lense have agonizingly slow AF too.

Lastly just because a lens got the red ring and the "L" name does not absolutely prove it has better IQ than any other lens. There are lots of non-L lenses that perform very well and can hold their own even some so called "kit" lenses as well.. Bottom line is if it works for you and does what you want don't worry about its name

Re: STM vs USM L glass difference

ebiggs1 — Wed, 27 Aug 2025 15:33:44 GMT

One further thought some guys are review addicts. They read or view any and all reviews possible on the ole inner web and that's where they draw their conclusions and experience form. I would be careful if your source is solely from reviews. I have been in the photography business for five decades and worked for a large company in KC that had a huge photography department. I don't read or watch reviews as a rule.

Re: STM vs USM L glass difference

FloridaDrafter — Wed, 27 Aug 2025 21:21:33 GMT

EB, I'm not a pixel peeper nor someone who reads or watches reviews to base my advice on. I actually own and use both lenses that the OP asked about and have for several years and I never comment on gear that I don't own and use. I've been using Canon gear for the past 30 years and trust it, although I do read Canons spec sheets before I buy, so I have no need for reviews 🙂

In your response, although you did eventually get around to it, it was buried deep in the post. You left out a very pertinent bit of the OP's question and went right to the 90% no difference thing. OP: "May I please ask in what situations there will be notable differences then? I am shooting families as a business, and I still want the best for my clients".

IMO, the second part of the question screams L glass all day long and should have been addressed straight away, particularly with the lenses in question (the RF 50mm f/1.8 STM and the RF 50mm f/1.2L USM), which I did. Honestly, if I used the 1.8 the way I use my 1.2L, it wouldn't be around long 😁 My wife likes the 1.8, but she shoots light, LOL!

Newton

Re: STM vs USM L glass difference

ebiggs1 — Thu, 28 Aug 2025 15:13:30 GMT

If what you are using is working for you and you are good with it, you have the right lenses. Don't matter what others or me say about it or what the name on the lens is "L" or no "L".

Not that it makes a hill of beans but I worked for a multimillion dollar company and my own photography business for decades and not once in either case did someone say, "Geez if you had only used 'such and such' lens that would have been a great shot." People put too much weight on what otter people think of them and what they are using or doing.

In my perhaps my unique situation I had the opportunity, plus my own hobby, to use or own 100's of lenses more than I can count. I probably have two dozen right now. Sometimes even duplicates of the same lenses. That's the big reason I don't read or watch reviews not that I have never seen one or read any. I don't even read the reviews about purchases when buying gear. You simply can not trust reviews. Most cases, not all but most, are one off and in no way represent the entire lot.

If you and your wife are happy with what you have so am I. Good shooting to both of you.

Re: STM vs USM L glass difference

FloridaDrafter — Thu, 28 Aug 2025 17:11:16 GMT

I get all of that and for the most part agree, but of the two lenses in question (not hundreds), I can't bring myself to recommend the consumer version of this lens series to a working or potentially working pro.

BTW, I have had clients ask what gear I use, not many, but a few 🙂

Newton

Re: STM vs USM L glass difference

ebiggs1 — Fri, 29 Aug 2025 14:28:46 GMT

" I have had clients ask what gear I use, not many, but a few"

After 40 years at my main job and about 50 years of my own business, no one has ever asked the question if only you used Canon's 1 series and all "L" lenses.. My second shooters, sometimes two sometimes just one, always used Rebels. My web site does state I use Canon equipment though. Along with Photoshop and Lightroom. It is a positive to let people know you have better or top notch gear. More so then scary uncle Bob or the next door neighbor who has a point & shoot and will shoot for free. People do like to think they are paying for the best.

Look no matter how you try to spin it, nobody cares what gear is used if they like the final photo. They just don't. If you think buying or recommending the most expensive gear and/or even the top notch gear is what it takes to make money as a photographer you have a lot to learn my friend.

Re: STM vs USM L glass difference

FloridaDrafter — Fri, 29 Aug 2025 23:12:16 GMT

"you have a lot to learn my friend."

Well, that may be, especially with the new era of photography that Canon has us in with mirror-less and fabulously brilliant optics that take advantage of the technology. I'm in my 70's and love the challenge of learning.

As I've mentioned several times, this thread is about two specific RF 50mm lenses and the OP has probably moved on. So, lets give it a rest please 🙂

Newton

Re: STM vs USM L glass difference

EK25 — Sat, 30 Aug 2025 02:48:54 GMT

Thank you so much for sharing these! Photos do look great and very sharp! This is off topic, but I am wondering why you are using such a high SS (and as a consequence, a high ISO) on the outdoor shots with seagulls as well as a couple shot (your daughter and her husband)? Also, which tools in PS are you referring to? I shoot in RAW, and prefer LrC to Ps, usually do sharpening and some denoising if necessary, but it sometimes does weird things to how things look, so I rely on good SOOCs...

Re: STM vs USM L glass difference

EK25 — Sat, 30 Aug 2025 02:59:20 GMT

Thank you so much for everyone's input, I truly appreciate it. I wish I could afford to buy the best glass - I am just not there in my career yet. But a last question though - if you were shooting with a mirrorless, and were to choose between EF L glass vs RF consumer grade STM glass, what would go with? Same price, both zooms (EF 24-70mm 2.8 L II USM vs RF 28-70 2.8 IS STM? Thank you very much in advance!

Re: STM vs USM L glass difference

EK25 — Sat, 30 Aug 2025 02:59:44 GMT

Re: STM vs USM L glass difference

EK25 — Sat, 30 Aug 2025 02:59:58 GMT

Re: STM vs USM L glass difference

FloridaDrafter — Sat, 30 Aug 2025 07:09:06 GMT

@EK25 wrote:

Thank you so much for sharing these! Photos do look great and very sharp! This is off topic, but I am wondering why you are using such a high SS (and as a consequence, a high ISO) on the outdoor shots with seagulls as well as a couple shot (your daughter and her husband)? Also, which tools in PS are you referring to? I shoot in RAW, and prefer LrC to Ps, usually do sharpening and some denoising if necessary, but it sometimes does weird things to how things look, so I rely on good SOOCs...

Hello, EK 25! You are welcome for the photos.

That's so cool that you caught that! I have a medical condition called "essential tremors", which causes me to shake pretty bad. I use a high shutter speed to counteract the tremors. Fortunately, my cameras handle ISO very well, so with IBIS and high SS it just works out for me. The shots in question were taken late in the day after the sun had gone down, so lighting was poor. ISO allowed me to get a fast SS and get a narrower aperture.

As for PhotoShop tools, I stopped using Adobe products when I retired so the images I posted were edited in DPP 4 then cropped and framed in Corel's PSP 25. All of those photos were barely touched in DPP and what adjustments I did use could easily be configure in one of the cameras picture styles, so they are pretty close to SOOC (that's why I posted those particular shots). The thing about Canon's DPP 4 is it uses their camera and lens profiles so when you use a lens that needs correction, it knows exactly what to apply. Not that LrC can't make the corrections, they just aren't the same as Canon's, IMO 🙂

Newton