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Canon EF 24-70/4L IS USM Review

by Bob Atkins, April 2013 (updated May 2013)


The Canon EF 24-70/4L IS USM, (compare prices) (review) is the latest addition to Canon’s f4 line of “L” series lenses. The f4 series are a stop slower than their f2.8 counterpoints, but much cheaper and those looking for high quality at low(er) cost and light(er) weight often chose to give up that extra stop of lens speed.

The EF 24-70/4L IS USM Macro is unique in the Canon lens lineup in that it is a zoom with a dedicated macro mode along with hybrid image stabilization. Hybrid IS is specifically designed to give much better stabilization results when a lens is used in the macro range.

EF 24-70/4L IS USM Macro Specifications

Elements/Groups 12 groups /15 elements (2 aspheric)
Angle of view (full frame) 84° – 34°
Closest Focusing Distance (normal mode) 0.38m / 1.25 ft.
Closest Focusing Distance (macro mode) 0.2m/ 8.9 in
Maximum Magnification 0.7x (in macro mode)
Diaphragm 9 blade (circular)
Filter Size 77mm
Focus Internal
Dimensions (Diameter x Length) 3.3 × 3.7 in. / 83.4 × 93mm
Weight 21 oz. / 600g

Externally, the EF 24-70/4L IS USM Macro is a typical Canon “L” series lens. It feels very sturdy and both focusing and zooming actions are smooth. There is a distance scale marked from 0.38m to infinity with IR focusing indicators for 24mm and 35mm.

Focal lengths are marked at 24mm, 35mm, 50mm and 70mm. Past 70mm there is a macro range which can be engaged by pushing the “Macro/Lock” switch towards “Macro” and rotating the zoom past the 70mm mark. It’s then in the macro range. To return to the normal focusing range the switch is again pushed towards “Macro” and the zoom ring rotated back into the normal range. The “Lock” position of the switch can be engaged when the zoom is set to 24mm. It then prevents the lens from extending.

The two other external switches are the “AF/MF” switch for selecting between auto focus and manual focus and the IS on/off switch. Manual focus is available at all time since the lens has full time manual focusing, so the real function of the switch is to turn AF on and off. The Image Stabilization has only two modes, on and off. There is no focus range limiting switch and no secondary IS modes for panning.

Focusing is internal, so the lens doesn’t extend and the front element doesn’t rotate during focusing. Zooming is not internal and the lens extends by about 3cm going from the 24mm setting to the 70mm setting giving an overall length of approximately 123mm (4.85"). Maximum extension in the macro range is only another 3mm (3.3cm in total).

Note that focusing distances are measured from the sensor, so when Canon quote a closest focus distance of 0.2m (20cm) in macro mode, that’s 20cm from the sensor. Since the front element of the lens is about 16.8mm from the sensor, the working distance (distance from the front element of the lens to the subject) is only slightly over 30mm (just over 1"). That’s pretty close and can make lighting the subject tricky at times. For purposes of comparison, the working distance of the Canon EF 100mm f2.8 macro lens is about 6" (150mm).

The EF 24-70/4L IS USM comes with a lens hood, but no case. The warranty is the standard Canon 1 year warranty. Canon states that the lens is weathersealed against dust and moisture.

Optical Characteristics

Unless otherwise stated, the optical characteristics of the EF 24-70/4L were obtained using and EOS 6D camera body.

Vignetting

At 24mm vignetting is quite noticeable. Wide open at f4 the corners are about 2 stops darker than the center. Stopping down helps, but even stopping down as far as f11 still leaves the corners almost a stop darker than the center. Vignetting with this lens can be corrected in-camera with cameras supporting that feature (e.g. EOS 6D), or it can be corrected post exposure on RAW files using Canon’s supplied DPP software.

Vignetting becomes less severe as the lens is zoomed out. In the 35-70mm range there’s about a stop of corner darkening at f4 and around 1/2 stop at f5.6.

Vignetting is much less of an issue when the EF 24-70/4L IS USM is mounted on a crop sensor body.

Distortion

Distortion is most noticeable at 24mm where it measures at around -2.5% (i.e. barrel distortion). In the center of the zoom range distortion is minimized and towards the long end of the range it switches sign to pincushion distortion. At 70mm it’s around +0.7%. Again distortion can be automatically corrected when RAW files are processed in Canon’s DPP software.

Chromatic Aberration

Chromatic aberration is very well controlled throughout the focal length range. It doesn’t vary much in extent as the lens is zoomed from 24mm to 70mm and it’s at a low enough level that it’s very unlikely to be an issue. Viewing images at 100% it’s barely detectable, even in the corners of the image. It can be automatically corrected for in-camera JPEGs by EOS bodies supporting that function, or it can be automatically corrected when RAW files are processed in Canon’s DPP software.

Sharpness

Sharpness is uniformly high across the whole focal length range. The image center is slightly sharper than the edges and corners, but even wide open the corners still rate as very good. Stopping down from f4 to 5.6 and f8 gives a slight increase in sharpness in the center and at the edges, but the improvement is small. Stopping down to f11 and smaller apertures results in decreased sharpness because of diffraction related softening.

The image on the right links to 100% crops from the center and edge of the image at 50mm f4 and 50mm f8. You’ll see that the f8 images are sharper, but remember that these are 100% crops and so even the f4 images are very good and would appear very sharp at normal print sizes.

This is a lens that can be shot wide open without worrying about significantly sacrificing image quality. However if you demand ultimate edge to edge sharpness and intend to make large prints, stopping down to f8 will give you slightly better sharpness.

Macro

The macro features of the 24-70/4L make it unique in the Canon lens lineup. First, it has a dedicated macro mode. That means it doesn’t just focus very close to get high magnification. Normal focusing stops at a distance of 0.38m. To get closer than that you have to push a switch forward which allows the zoom to go “past” the 70mm normal limit and into a “macro range”. Once in the macro range the switch has to be pushed forward again to get out of the macro range. I assume that this transition is associated with some internal rearrangement of the lens’ optics to allow higher magnification and minimize aberrations.

The second macro feature is the inclusion of a hybrid IS system such as is also used on the EF 100/2.8L IS USM macro lens. The hybrid system not only compensates for the usual angular movements of the lens (“pitch” and “yaw”), but also for horizontal and vertical shifts. While straight horizontal and vertical shifts don’t move the image much in normal non-macro situations, they become very important at high magnification. Normal IS really doesn’t do a whole lot for macro lenses operating near 1:1, Hybrid IS can give an effective 2 stop stabilization.

It should be understood of course that this is a normal zoom lens with macro capability, not a dedicated macro lens. Dedicated macro lenses have an optical design to minimize aberrations and flatten the field. Since they don’t also have to zoom they can be quite complex designs and achieve very high image flatness and sharpness, even when used wide open. The 24-70/4L has to do a lot of jobs, and while it should be better than most close focusing zooms, and give a higher magnification, it can’t really be expected to rival the performance of a dedicated macro lens.

All that being said, the EF 24-70/4L IS USM that I looked at appeared to have a problem. It exhibited focus shift on stopping down when used in the macro mode. Normally all lenses focus at maximum aperture, even if they are set to shoot stopped down. This is because focus is more accurate a large apertures because DOF is smaller and therefore the range over which the image appears to be sharp when focusing is smaller. However, in the presence of enough uncorrected spherical aberration, optimal focus wide open may be different from optimum focus stopped down.

This appears to be the case with the EF 24-70/4L. I did some careful tests using AF, and manual focus (LiveView) using a special high resolution, optically flat chrome on glass target. It appears that focus moves back (away from the lens) very slighly when the lens is focused at f4 and then shot at f8

The shift is real and its effect on resolution at f8 (and f5.6 and f11) can be observed when shooting a flat target. It’s not really observable at f16 and smaller apertures on images of flat targets because the increased depth of field pretty much cancels out the effects of the focus shift.

While this sounds bad, in practice it’s actually not as much of a problem as it sounds. In fact, if you were just shooting images of 3-dimensional subjects (insects, flowers etc.) it’s possible you wouldn’t even notice it. You’d get a reduction in resolution in the focus plane at f8, but resolution would be high in a slightly different focus plane, in fact one close enough to where you wanted that the image would probably look just fine almost all the time. If you were shooting flat subjects like coins, postage stamps or banknotes, then you would probably notice it a lot more.

The image on the right (click for larger version) was shot using AF (at f4) and exposed at f8. Any slight focus shift hasn’t really affected the image. Looks just fine to me. I wouldn’t have suspected a focus shift from this image.

My gut feeling is that the macro mode focus shift probably won’t bother most users. In fact unless they read this or some similar review, they may not even notice it. It’s certainly not a “deal breaker”, though it would certainly have been nicer if it hadn’t been there.

It’s possible of course that I’m seeing something not typical of the lens. After all I tested only one sample. So I did a search to see if anyone else had seen a similar issue and I found a couple of reports of suggesting the same thing, so it doesn’t look like an isolated case.

Conclusions

The Canon EF 24-70/4L IS USM, (compare prices) (review) is a very good lens. It’s sharp wide open and that sharpness extends across the whole frame and across the whole focal length range. It does sharpen up a bit by stopping down to f5.6 or f8, but you certainly don’t need to stop down for sharp images. The IS system is very effective and the lens is smaller, lighter and around $700 less expensive than the EF 24-70/2.8L II IS USM. On top of that it’s also a very useful macro lens (despite the focus shift).

One obvious alternative would be the Canon EF 24-70mm f/2.8L II USM, (compare prices). This is Canon’s premium mid range zoom and commands a premium price – but delivers premium performance and it’s a stop faster then the f4 version. If you need the speed and the ultimate in sharpness, it’s the lens to get. If you don’t, the f4 version might be a better buy for a lot of photographers.

A second alternative would be the Canon EF 24-105mm f/4 L IS USM, (compare prices) (review). It’s the same speed, has a longer zoom range and it’s around $350 cheaper. On the other hand it doesn’t have a macro mode (max magnification is 0.23x vs. 0.7x), it doesn’t have hybrid IS and the IS it does have is rated by canon a “up to 3 stops”, while the new 24-70/4L’s IS system is rated by Canon as “up to 4 stops”. The EF 24-105/4L also has more distortion and vignetting at 24mm than the 24-70/4L.

Where to Buy

Canon EF 24-70/4L IS USM
Price as low as $1379.95 from 3 retailers
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Canon EF 24-70/4L IS USM, (compare prices) (review). From usa.canon.com: The EF 24-70mm f/4L IS USM is the perfect zoom to complement full-frame DSLRs like the EOS 6D. With 2 aspheric and 2 UD elements, the EF 24-70mm f/4L IS USM delivers high- quality images with excellent detail throughout the entire zoom range.


Text and photos © 2013 Bob Atkins.

Article revised May 2013.

Readers' Comments


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Timo Junttila, February 23, 2014; 10:12 A.M.

Thank you for the review, it was really informative and helpful. I recently ordered the 6D combination with this lense and I'm anxiously waiting to try it!


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