STM vs USM L glass difference

[EK25]

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!

[kvbarkley]

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.

[ebiggs1]

"... 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.

[EK25]

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. 

[EK25]

Thank you so much, this is helpful!

[kvbarkley]

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

[FloridaDrafter]

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@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. 

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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

[deebatman316]

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.

[ebiggs1]

" 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

[ebiggs1]

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.