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Canon 40mm f/2.8 STM
EF Full-Frame
Pancake (2012-today)

© 2015 KenRockwell.com. All rights reserved.

Intro   Specs   Performance   Compared   Usage   Recommendations   More

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Canon 40mm f/2.8 STM

Canon EF 40mm f/2.8 STM (52mm filter thread, 1'/0.3m close-focus, 4.4 oz./124g, about $150 after rebate.) enlarge. I got mine at Adorama, you also can get them at Amazon and at B&H

My biggest source of support for this ad-free website is when you use those or any of these links when you get anything, regardless of the country in which you live. It helps me keep adding to this free website when you get your things through these links — but I receive nothing for my efforts if you buy elsewhere. Thanks for your support! Ken.


January 2015    Canon Reviews    Canon Lenses    All Reviews

Why Fixed Lenses Take Better Pictures


Sample Image File

Hot Off The Grill 19 August 2012

Chelsea Diner, 19 August 2012. 5D Mark III, 40 STM wide-open at f/2.8 at 1/40 hand-held, AUTO ISO 125, +4 Saturation, 6 sharpening, A4 Auto White Balance.) Camera-Original © 5MB LARGE JPG File, no lens aberration correction.

This is wide-open at f/2.8 with no correction for fall-off or lateral color fringes. This lens is super-sharp out to the edges wide-open, and remember in this real-world example, the only thing really in perfect focus is the stack of plates in the middle.


Introduction       top

Intro   Specs   Performance   Compared   Usage   Recommendations   More

Adorama pays top dollar for your used gear.

B&H Photo - Video - Pro Audio

This Canon EF 40mm f/2.8 STM is a tiny lens with superb optical performance. This tiny thing isn't much bigger than a lens cap, and has unbeaten optics.

40mm is the "Perfect Normal" focal length for full-frame. Unlike 50mm lenses which often are too long or 35mm lenses which are often too wide, 40mm is always just right.

40mm matches full-frame's diagonal, especially when cropped a little from the left and right. 50mm has always been a little long as a normal lens; 50mm just happened to be what LEICA already had handy in the lab when the first 35mm camera was kludged together in 1918. 50mm stuck as a common "normal" focal length because it was cheaper and easier to make good 50mm instead of 40mm lens before the 1960s due to the smaller angle covered, and after the 1960s, 50mm stuck because it's much, much easier to clear the flipping mirror of an SLR with a 50mm lens, but the 40mm to 45mm range (precisely 43.27mm) is what's really normal for the 35mm full-frame.

This new-technology STM lens is completely compatible with all Canon EOS cameras made since 1987, including 35mm, full-frame, 1.3x and 1.6x sensor cameras. It works as well on my EOS 3 on Velvia 50 as it does with the 5D Mark III or Rebel T4i.

The 40/2.8 STM uses a different kind of autofocus motor, called STM (stepper motor) for quieter AF, especially intended for use while shooting video with a DSLR.

There is immediate manual-focus override simply by turning the front ring, but it's weird: it's done electronically, so the focus ring isn't connected to anything. There is a tiny time delay between when you move the ring and the lens moving. The speed at which the lens moves isn't directly related to how far or how fast you turn the ring, so it's weird. It's not as good as having a real manual focus ring like the 50/1.4 USM or 35/1.4 L.

This new STM motor is not silent. It makes a quiet hum while moving, usually quieter then other EF lenses, but by no means silent. The STM motor in the 18-135 STM is silent, but not quite in this 40mm.

The STM motor does not focus faster than other lenses. It's about as fast as my 50mm f/1.8 II and not quite as fast as my EF 28mm f/1.8 USM. The 40/2.8 STM is quieter than the 50/1.8, and about as quiet as the 28/1.8.

Enough with the STM motor; the optics of this lens are superb, and its size make it a complete winner for just $200.


Compatibility and Formats

This lens is optimized for 35mm film and full-frame digital, and of course works on all 1.3x and 1.6x Canon cameras.

This Canon EF EOS 40mm f/2.8 STM works perfectly with every Canon EOS camera ever made, meaning every Canon DSLR and every Canon autofocus 35mm camera made since 1987.

Of course it works great on today's 5D Mark III and Canon 7D, but it also works great on my original 1987 Canon EOS 650! The only oddness I noted on my 1987 EOS 650 is that while auto and manual focus and depth-of-field preview and everything work great, manual focus override doesn't work: you have to set the lens to manual first. Manual-focus override works flawlessly on my 35mm EOS Rebel G from 1996 and EOS 3 from 1998, so I'm not worrying about it.

As a full-frame lens, this works on all Canon EOS cameras, regardless of format. As a full-frame lens, I will be reviewing this lens on full-frame unless otherwise mentioned.


Canon 40mm f/2.8 STM

Canon 40 2.8 STM. enlarge.


Specifications         top

Intro   Specs   Performance   Compared   Usage   Recommendations   More



Canon calls this the CANON LENS EF 40mm f/2.8 STM.

EF means "electronic focus," meaning that there is an autofocus motor in the lens itself. All Canon lenses since 1987 have been EF.

STM means that the AF motor is a stepper motor.

∅52: 52mm filter thread.


Optics       top

6 elements in 4 groups.

One aspherical element.

Coated mostly in amber and blue, with one green surface seen.

Unit focus observed (the whole thing moves in and out), but Canon claims internal focus.


Focal Length


Used on a 1.3x camera, it will see about the same field of view as a 52mm lens sees on full-frame.

Used on a 1.6x camera, it will see about the same field of view as a 64mm lens sees on full-frame.


Angle of View (on 35mm and full-frame cameras)

57.5º diagonal.

34º vertical.

49.3º  horizontal.


Close Focus       top

1 foot (12" or 0.3 m) from the image plane, specified.


Maximum Reproduction Ratio       top

1:5.6 (0.18x).

With EF12 tube: 1:2 (0.50x).

With EF25 tube: 1:1.1 (0.88x).


Diaphragm       top

Canon 40 2.8 STM

Front, Canon 40mm at f/2.8 STM at f/2.8 (EF diaphragm not seen). bigger.

7 rounded blades.

Stops down to f/22.

Round to f/5.6, heptagonal from f/8 to f/22.


Focus Scale       top


The ring turns without stops; it's just an electronic encoder.


Depth-of-Field Scale       top



Infra-Red Focus Indices       top



Filters        top

52mm thread, plastic.

Does not rotate, but does move in and out with focusing.


Size       top

Canon specifies 2.7 " (68.2 mm) diameter by 0.9 " (22.8 mm) long.


Weight       top

4.390 oz. (124.5 g), measured.

Canon specifies 4.6 oz. (130 g).


Hood       top

Plastic screw-in ES-52, optional. I wouldn't bother with it.


Case       top

LP811 sack, $24.

I'd use a tube sock instead.


Caps       top

Standard 52mm front cap.

Oddly, this STM lens only gets the regular front cap, not the one with ULTRASONIC in gold as Canon uses for their fancier ultrasonic lenses. No big deal, the Nikon 52mm cap is better than any of these.

Standard EOS cap rear.


Quality       top

Made in Malaysia.


Introduced       top

07 June 2012, 12:09 AM, New York City time.


Price, USA        top

2015 January: $150 after rebate.

2012 June-2013 May: $200. (In Japan, 23,000 yen suggested retail price.)

Canon EF 40mm f/2.8 STM Box

Box, Canon EF 40mm f/2.8 STM.

Performance       top

Intro   Specs   Performance   Compared   Usage   Recommendations   More

Overall    Autofocus    Breathing   Color   Distortion   Ergonomics

Falloff    Filters     Flare     Lateral Color Fringes

Macro   Mechanics   Sharpness   Sunstars


Overall     performance      top

The Canon 40mm f/2.8 STM is the tiniest lens ever made by Canon for its EOS system. It's not the lightest; the 50/1.8 II is 2 grams lighter.

This 40mm lens is optically unsurpassed, even without a lens profile on the 5D Mark III.


Autofocus     performance      top

Autofocus is as fast as other Canon lenses. It's fast, but it isn't silent.


Auto/Manual Switching

Just grab the focus ring for instant manual-focus override in ONE SHOT mode. In AI SERVO, the camera will keep trying to focus for you.

You never need to touch the AF-MF switch unless you want to lock-out autofocus.


AF Speed

AF is as fast as most other Canon EF lenses.


AF Noise

AF is quieter than most Canon EF lenses.

It sounds like a stepper motor: a quiet, precise hum.

When the lens is constantly moving in and out in AI SERVO mode for video, it is quieter than other USM lenses since it doesn't make mild banging noises as it reverses direction.


AF Accuracy and Consistency

AF accuracy is dead-on on my Canon 5D Mark III, T4i and EOS 3.

At a slow f/2.8, this isn't very difficult.


Manual Focus

Manual focus is worse than other Canon lenses.

The ring is merely an input to a computer, which in turn controls the lens motor.

It only works if the camera is both on and awake. On some cameras, it only works if your finger has the shutter half pushed down, even when it is awake.

There is little direct relationship between the motion of the ring and the motion of the lens, and there is some time delay.

Get the EF 50/1.4 USM, Voigtländer 40mm f/2 or EF 35/1.4 L if you need great manual focus.


Focus Breathing     performance      top

Focus breathing is of interest to cinematographers who don't want the image changing size ("breathing") as the lens is focused among different subjects.

The image of the Canon 40mm f/2.8 STM gets larger as focused more closely.


Color Rendition     performance      top

The color balance of this 40mm f/2.8 matches my other Canon EF lenses.


Distortion     performance      top

This Canon 40/2.8 STM has no measurable distortion at 10 feet (3 meters) as tested on both full-frame as well as 1.6x cameras, even without a lens profile.

This means that whatever distortion it may have is below the 0.05 level in Photoshop's Lens Distortion tool.


Ergonomics     performance      top

Canon 40mm f/2.8 STM

Canon 40/2.8 STM.

Ergonomics are perfect, just grab and go, with the exceptions already made about the weird-responding manual focus ring.


Falloff (darkened corners)     performance      top

Shot on modern full-frame cameras with a lens profile loaded and peripheral illumination correction enabled, there is no visible falloff.

Shot on 35mm or with full-frame digital cameras without peripheral illumination correction, there is some falloff at f/2.8, and it's gone by f/4.

I've greatly exaggerated this below by shooting a flat gray target and presenting these images against a flat gray background:


Canon 40mm f/2.8 STM falloff on full-frame

No peripheral illumination correction

Canon 40mm f/2.8 STM Falloff Canon 40mm f/2.8 STM Falloff
Canon 40mm f/2.8 STM Falloff Canon 40mm f/2.8 STM Falloff

© 2012 KenRockwell.com. All rights reserved.



Filters, Use with     performance      top

52mm is a huge filter size for the tiny optics of this lens.

It works without vignetting with many stacked filters, but watch it: Canon cautions to use just one so you don't damage the wimpy internal mechanics of the focus mechanism.


Flare and Ghosts     performance      top

The 40 STM has no visible ghosts.

This is as bad as I could make it look, and this is with a multi-coated L37c (370 nm UV) filter over the lens:

Noni's park 19 August 2012 Katie on left

Ghosts. Canon 40/2.8 STM with Nikon L37c filter, f/5 at 1/100 at ISO 100 on 5D Mk III, 6 sharpening +4 saturation. bigger. (That's Katie shooting hoops on the right.)

See the green dot in the center right? That's a reflection from the sensor back to the filter and then back to the sensor. Remove the filter, and that dot goes away. You'll get inverted dim ghosts of whatever color the filter's coatings make them.

If these bother you (I was only able to make one shot like this no matter how many other times I tried), take off the filter first.


Lateral Color Fringes     performance      top

There are no color fringes even when shot without a lens profile on the 5D Mk III.

This is superb performance.


Macro    performance      top

Macro is sharp but not particularly close:

Canon 40mm macro 09 July 2012

At close-focus distance, f/5 at 1/125 at ISO 100, full-frame Canon 5D Mark III, hand-held, +4 saturation, 6 sharpening.

This is on full-frame. Shot on Canon's smaller-format 1.3x and 1.6x cameras, the effect will be even closer.

Canon 40mm macro

Crop from above image at 100%, 22 MP Canon 5D Mark III.

You can see all the dirt on my watch crystal.


Mechanics     performance      top

Canon 40mm f/2.8 STM

Rear, Canon 40 f/2.8 STM.

The Canon 40mm f/2.8 STM is a decent lens, made entirely of plastic, with a metal mount. Since the mount is half the lens, it feels pretty tough, even if the internal mechanism may not be.


Filter Threads



Hood Mount

None, you use the filter threads.


Fore Barrel



Focus Ring

Rubbery plastic.


Main Barrel




Seem like all plastic.


Moisture seal at mount




Chromed metal.





Serial Number

Canon EF 40mm f/2.8 STM

Bottom, Canon EF 40mm f/2.8 STM.

Laser-engraved into bottom of lens barrel.


Date Code

None found.


Noises When Shaken

Mild clicking.


Made in



Sharpness     performance      top

Lens sharpness doesn't matter much, but it sure distracts amateurs who confuse lens sharpness with picture sharpness.

Hot Off The Grill 19 August 2012

Chelsea Diner. 5D Mark III, 40 STM at f/5.6 at 1/160 hand-held, AUTO ISO 100, +4 Saturation, 6 sharpening, A4 Auto White Balance.) Camera-Original © 7.5MB LARGE JPG File, no lens aberration correction.

The Canon 40mm is insanely sharp at every setting throughout the entire full-frame on the 22 MP 5D Mark III.

Likewise, it's always super-sharp on 1.6x cameras like the 1.6x Rebel T4i. However, at full 18 MP resolution on a small-format DSLR, the corners were slightly less sharp wide-open improving as stopped down to f/8.

If softens from diffraction by f/8, meaning that it's pretty much a perfect lens at f/5.6!

Here is Canon's rated MTF curve:

Canon 40mm MTF at 8mmCanon 40mm f/2.8 STM MTF.

Hot Off The Grill HOTG entrance 20 August 2012

NYC Subway Entrance. 5D Mark III, 40 STM at f/9 at 1/400 hand-held, AUTO ISO 100, +4 Saturation, 6 sharpening, A4 Auto White Balance.) Camera-Original © 8MB LARGE JPG File, no lens aberration correction.


Sunstars     performance      top

With a rounded 7-bladed diaphragm, sunstars have diffuse, not sharp, points.

There surprisingly are sunstars at most apertures, although they are soft.

For the best sunstars, shoot at f/11 or smaller.


Compared       top

Intro   Specs   Performance   Compared   Usage   Recommendations   More

The Voigtländer 40mm f/2 is the same size and is much better made out of all metal, but is manual-focus only. It weighs a little more, at 6.337 oz. (179.6g), and costs more, at $539. It's a stop faster, and just as extraordinarily sharp.

The Canon 50mm f/1.8 II focuses as quickly and weighs 2 grams less, but is bigger and has only a plastic mount. It costs only half as much, has more distortion, and isn't quite as sharp at f/2.8, but is as sharp at f/4 and smaller.


Usage         top

Intro   Specs   Performance   Compared   Usage   Recommendations   More

Since even manual focus is electronic, there is no manual focus when the camera is off or asleep. On some cameras, manual focus only works with the shutter button held.

For immediate manual-focus override, you have to be in ONE SHOT AF mode. In AI SERVO mode, most cameras keep trying to change the focus on you, while other cameras simply ignore manual focus in AI SERVO.

Canon suggests to update the firmware of your 1D Mark IV to version 1.1.1 or newer for the best exposure accuracy.

Canon also suggests to update your 5D Mark III, but even with older 1.0.7 software in my 5D Mark III, this lens works great. I have no lens profile with my older firmware and software, but no worries; this lens is so good and needs no correction except for falloff at f/2.8, that I can't be bothered to waste the time to update my camera.

On 35mm EOS cameras, Canon warns that AF may be slower with low batteries or in low temperatures. No worries, for me, it's just as fast on my 1987 EOS 650 as it is on my 5D Mark III!


Hood       top

I'd forget the little ES-52 hood. It's an idiotic thing that won't actually shield any light.

The snap-on metal Nikon HS-6 works great, and you could use an even longer one if you wanted. The snap-on metal Nikon HS-14 is just barely too long. You get the idea; any screw-in or snap-on 52mm metal, plastic or folding rubber hood ought to work great.

Be careful with hoods; if you use a metal screw-in hood you'll rip this plastic lens' guts out if you snag or bang the hood on something.

I had no problems with flare without a hood, so I'd forget it entirely. A hood would double the size of this thing!


Recommendations       top

Intro   Specs   Performance   Compared   Usage   Recommendations   More

This Canon 40mm f/2.8 STM is an excellent lens for just about anything.

If you like to take everything but still travel light, add the 20mm f/2.8 USM and the 85mm f/1.8 USM or 70-200/4 IS L, and you're good to go for anything, anywhere. (Skip a wide zoom like the 17-40mm L, it duplicates 40mm. See Assembling a System; you don't want to cover every millimeter.)

If you've found the time I've spent sharing this professional review helpful, this free website's biggest source of support is when you use these links, especially these links directly to it at Adorama or at Amazon, when you get anything, regardless of the country in which you live.




More Information       top

Intro   Specs   Performance   Compared   Usage   Recommendations   More

Canon USA's 40mm STM product page.

Canon USA's 40mm STM instruction manual.

Canon Japan's 40 STM Page (Japanese; English Translation).


Help me help you         top

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The biggest help is when you use any of these links when you get anything, regardless of the country in which you live. It costs you nothing, and is this site's, and thus my family's, biggest source of support. These places have the best prices and service, which is why I've used them since before this website existed. I recommend them all personally.

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Mr. & Mrs. Ken Rockwell, Ryan and Katie.


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August 2012, May 2013, Jan 2015