As I looked forward to creating the Canon EF 70-300mm f/4-5.6 L IS USM Lens review, I knew that Canon's introduction of this lens was going to make my life more difficult - but in a good way. I spend a lot of time helping people select the proper lens for their needs and budget, and even before the 70-300 L was announced, there was a large selection of pro-grade Canon telephoto zoom lenses available. These include the four 70-200 L lenses and the 100-400 L. Adding the EF 70-300mm f/4-5.6 IS L USM Lens to the Canon telephoto zoom lens lineup simply adds another excellent option to this list - increasing the difficulty of selecting the ideal lens for someone.
Let's look at the at-review-time Canon telephoto zoom lens lineup along with a couple of telephoto primes lenses included.
|Model||Weight||Dimensions w/o Hood||Filter||Year|
|Canon EF 70-200mm f/4.0 L USM Lens||24.9 oz||(705g)||3.0 x 6.8"||(76 x 172mm)||67mm||1999|
|Canon EF 70-200mm f/4.0 L IS USM Lens||26.8 oz||(760g)||3.0 x 6.8"||(76 x 172mm)||67mm||2006|
|Canon EF 70-200mm f/2.8 L USM Lens||46.2 oz||(1310g)||3.3 x 7.6"||(85 x 194mm)||77mm||1995|
|Canon EF 70-200mm f/2.8 L IS II USM Lens||52.6 oz||(1490g)||3.5 x 7.8"||(89 x 199mm)||77mm||2010|
|Canon EF 70-300mm f/4-5.6 IS L USM Lens||37.1 oz||(1050g)||3.5 x 5.6"||(89 x 143mm)||67mm||2010|
|Canon EF 70-300mm f/4-5.6 IS USM Lens||22.2 oz||(630g)||3.0 x 5.6"||(76.5 x 143mm)||58mm||2005|
|Canon EF 70-300mm f/4.5-5.6 DO IS USM Lens||25.4 oz||(720g)||3.2 x 3.9"||(82 x 100mm)||58mm||2004|
|Canon EF 75-300mm f/4-5.6 III USM Lens||16.9 oz||(480g)||2.8 x 4.8"||(71 x 122mm)||58mm||1999|
|Canon EF 100-400mm f/4.5-5.6 L IS USM Lens||48.7 oz||(1380g)||3.6 x 7.4"||(92 x 189mm)||77mm||1998|
|Canon EF 300mm f/4.0 L IS USM Lens||42.0 oz||(1190g)||3.5 x 8.7"||(90 x 221mm)||77mm||1997|
|Canon EF 400mm f/5.6 L USM Lens||44.1 oz||(1250g)||3.5 x 10.1"||(90 x 257mm)||77mm||1993|
For many more comparisons, review the complete Canon EF 70-300mm f/4-5.6 L IS USM Lens Lens Specifications using the site tool. With the information in this chart, including the information in the lens names, we can start slotting the 70-300 L IS into the lineup.
From a physical length standpoint, the 70-300 L is on the short side (when retracted). Here is a visual look at most of these lenses, in order from shortest to longest in fully-retracted position.
You are looking at, from left to right, the following lenses:
Canon EF 70-300mm f/4.5-5.6 DO IS USM Lens
Canon EF 70-300mm f/4-5.6 IS USM Lens
Canon EF 70-300mm f/4-5.6 IS L USM Lens
Canon EF 70-200mm f/4.0 L IS USM Lens
Canon EF 100-400mm f/4.5-5.6 L IS USM Lens
Canon EF 70-200mm f/2.8 L IS II USM Lens
Canon EF 300mm f/4.0 L IS USM Lens
Canon EF 400mm f/5.6 L USM Lens
Pictured below are the same lenses in the same sequence in their fully-extended positions.
My first thought when picking up the Canon EF 70-300mm f/4-5.6 L IS USM Lens for the first time, after having used the other comparative lenses extensively, was that this is a light-in-weight but wide-in-diameter lens. As the earlier chart shows, the 70-300 L is the lightest L lens in this class (with the exception of the two small 70-200mm f/4 L Lenses) and it is nearly as wide as the longer and heavier EF 100-400 L. Retracted, the 70-300 L is the shortest L lens on this list - and remains shorter than most even when extended. It even fits nicely into a mid-sized Lowepro Toploader Pro 70 AW Case when mounted on a pro-sized EOS body.
A 70-something mm telephoto zoom lens complements a general purpose lens very nicely. This is typically the focal length range I recommend to someone looking for their second lens (unless they have a specific application that 70-something does not work well for of course) In terms of focal length range, the 70-300 L is a match for the other 70-300mm zooms, exceeds the 70-200's range and sacrifices some of the 100-400's reach for some wide angle advantage.
Following is a sampling of the focal lengths available in the Canon EF 70-300mm f/4-5.6 L IS USM Lens.
The above examples were shot with the full frame Canon EOS 1Ds Mark III DSLR.
A penalty normally paid for a long focal length range in a reasonably-sized lens is the variable maximum aperture. This means that your exposure parameters must change over the focal length range if an aperture wider than is available at the zoomed-to focal length has been selected prior to that zooming. Here is how the max aperture step-down comparison shapes up.
|Canon EF 70-300mm f/4-5.6 IS L USM Lens||70-103mm||104-154mm||155-228mm||229-300mm|
|Canon EF 70-300mm f/4-5.6 IS USM Lens||70-84mm||85-134mm||135-224mm||225-300mm|
|Canon EF 70-300mm f/4.5-5.6 DO IS USM Lens||70-94mm||95-184mm||185-300mm|
|Canon EF 75-300mm f/4-5.6 III USM Lens||75-94mm||95-139mm||140-239mm||240-300mm|
|Canon EF 100-400mm f/4.5-5.6 L IS USM Lens||100-129mm||130-259mm||260-400mm|
Comparable zoom lenses omitted from this table are the fixed max aperture and overall wider max aperture 70-200mm L lenses. Otherwise, wider apertures at similar focal lengths within this group represent a win. And the Canon EF 70-300mm f/4-5.6 L IS USM Lens compares well here.
Basically, the 70-300 L slots nicely between the 70-200 L lenses and the 100-400 L lens with focal length range, aperture and size/weight being significant differentiators. And though it slots above the previous Canon EF 70-300mm lenses in terms of size, it slots well-above them in terms of image quality. I'll come back to more comparisons later in this review.
As you probably noticed by now, the 70-300 L does indeed extend - by 2.11" (53.4mm) at 300mm. Unique is how narrow, relative to the lens diameter, the extending portion of this lens is - resulting in filter threads that are only 67mm in diameter. Also unique is that much of the extending portion of this lens is white with the balance of the objective end being black (tiny black screws attach this separate, smoothly-integrated black piece to the white barrel). To my eyes, the lens appears somewhat unusual because of these attributes. But it definitely works well.
Showing its Canon L Lens status, the Canon EF 70-300mm f/4-5.6 L IS USM Lens is a very well built, high quality lens. You will feel this quality immediately upon picking up the lens.
The zoom and focus rings are very smooth with no play - and the zoom ring remains very smooth even while the lens is pointed up or down. Both rings are nicely sized and very well integrated into the lens barrel design. What I do not like is the rear-positioned focus ring design. The focus ring is in the position where I want the zoom ring to be. I find it too easy to unintentionally change focus while final-framing a subject - especially when correcting for my HLDS (Horizon-Level Deficiency Syndrome). And I find that I am less steady when holding out farther on the lens where the zoom ring is located. I do like this design a little better than the Canon push-pull zoom design found in the 28-300 L and 100-400 L.
Space can be seen on the lens barrel above for the optional Canon Tripod Mount Ring C (WII) as shown on the lens below.
Right, I said "optional". To date, Canon has included a tripod ring on all of its white EF lenses other than the two 70-200 f/4 L Lenses and my personal opinion is that they should have included it on this one as well. If using a tripod or monopod, you are going to appreciate having the balanced setup the ring provides for as this lens is rather heavy to have hanging out over a tripod head. Two downsides are that the Canon Tripod Mount Ring C (WII) (at review time at least) is over-priced and and that it is not the smoothest tripod ring I've used - I can hear metal rubbing against metal when rotating the ring.
Another benefit to the tripod ring is that, especially with a Wimberley P20 Lens Plate installed, I have a close-to-the-camera grip alternative to the focus ring.
Also following the lead of the EF 70-200mm f/4 L lenses is the inclusion of a soft lens case (the Canon LP1424 shown above) instead of the nicer padded and zippered cases the rest of the similarly-sized and similarly-priced white L lenses come with. The Canon EF 70-300mm f/4-5.6 L IS USM Lens, with its lens hood reversed, fits snugly (length-wise) in a Lowepro Lens Case 4S, snugly width-wise in a Lowepro Lens Exchange 200 AW and also fits in the Lowepro S&F Slim Lens Pouch 75 AW. It still fits in these cases even with the optional tripod ring and a Lens Plate installed, but the fit is snug width-wise in all three cases.
As with all current-at-review time L lenses, the lens hood is included in the 70-300 L box (Canon ET-73B Lens Hood). The hood sports the recently adopted and very nice matte finish design (it does not show marks nearly as easily). This is a rather deep hood that, when installed, makes installing/removing the Canon side-pinch-only lens caps somewhat difficult (but doable). The depth of this lens is very protective for the front element. I have found it especially valuable for keeping salt water spray off of the front lens element.
I have not heard doing so condoned by Canon, but the round hood allows the lens to be set on a flat surface with a camera mounted to it - and I frequently do this. I of course do not recommend putting any stress on this setup and you are of course at your own risk when using the lens hood as a camera stand.
The 70-300 L IS includes a zoom lock switch. Use this switch to prevent gravity- or inertia-extension of the lens when it is not in use (or when shooting at 70mm). My copies of this lens had no real need for this switch, but perhaps they will need it after a significant amount of use.
A rubber gasket can be seen near the lens mount - this is a weather-sealed lens. It has been confirmed to me that this lens, like most other non-super telephoto lenses, requires a filter for complete sealing.
How sealed is a sealed lens? That is always the big question. My *understanding* is that weather sealed EF lenses are definitely not immersible, but they can handle rain without a problem.
I have shot with the 70-300 L in light rain without problems. A much bigger sealing test came two days into a long photography trip to Maui, Hawaii. The 70-300 L and I took a direct hit from a rogue wave. I was standing on a high, narrow (and very dry) volcanic rock to get a better angle for shooting waves. A wave came completely over me, the 5D III and the 70-300mm L Lens I was using. A major amount of water was running off of the camera, lens and me - like a waterfall.
I fortunately maintained my balance, but I was not pleased to see the substantial amount of salt water on my gear. I quickly ran to the car and dried everything with a towel (I typically have one along when shooting in such an environment). I didn't expect to have any problems and was relieved to find both the camera and lens to be working fine. And they both continue to work fine. Weather sealing has definite value.
You are of course on your own when exposing camera gear to the elements.
While Canon has been using fluorene over the anti-aliasing filters on sensors for years, the Canon EF 70-300mm f/4-5.6 L IS USM Lens is the first lens to receive this treatment. Fluorine anti-smear coating has been applied to the 70-300 L's front and rear elements. I have to admit that this feature did not generate much enthusiasm from me at announcement time, but I did some testing to amuse myself. And having done so, I now have to say that I'm impressed.
I touched the front lens element of the 70-300 L and two other lenses (one Canon L, one Tamron) with a very body-oily finger tip. The 70-300 L was noticeably easier to clean than the other two lenses - I basically wiped the oil right off the lens with only a swipe of a microfiber cloth. The fluorene coating is going to be especially useful in the field where the dirt typically shows up most frequently and liquid cleaning supplies are not always available. Note: a microfiber cloth should always be with you.
Also new is the new white color this lens is sporting. The change is rather subtle, but can be seen by toggling back and forth between lens images in the site's Product Image Comparison Tool. I think the change is a mildly positive one cosmetically.
New for mid-2010 is that Canon's lenses are arriving with a longer 10-digit serial number and absent the previously standard date code. There is no date code visible on my 70-300 L IS.
Powered by Ring USM (Ultrasonic Motor), the Canon EF 70-300mm f/4-5.6 L IS USM Lens focuses very quickly and quietly without extending the lens. The filter threads do not rotate - this is an important attribute when using some filters including Circular Polarizer Filters. FTM (Full Time Manual) focusing is featured - but because of the focus ring position, I'd almost rather it was not a feature - or able to be disabled.
One-shot AF accuracy has been excellent and I found AI Servo accuracy to be quite good. I even had some front-focused AI Servo shots (focused in front of the subject) with a fast-closing subject. This is unusual as back focusing is far more common in this situation. I have found the 70-300 L to focus hunt more frequently than I am used to with lenses of this grade.
Videographers will appreciate the smooth 150º focusing ring rotation and subject framing that does not change with focusing. Zoom ring rotation is 92º - and very smooth.
Canon indicates that this is not a parfocal lens (that at least slight changes in focus distance settings are required as the focal length is changed). However, focusing at 300mm gives very sharp results at all marked focal lengths except 100mm (and 70mm is slightly soft). So Canon is correct, but this lens is at least partially usable as a parfocal lens.
|Canon EF 70-200mm f/4.0 L USM Lens||47.2"||(1200mm)||.21x|
|Canon EF 70-200mm f/4.0 L IS USM Lens||47.2"||(1200mm)||.21x|
|Canon EF 70-200mm f/2.8 L USM Lens||59.1"||(1500mm)||.13x|
|Canon EF 70-200mm f/2.8 L IS II USM Lens||47.2"||(1200mm)||.21x|
|Canon EF 70-300mm f/4-5.6 IS L USM Lens||47.2"||(1200mm)||.21x|
|Canon EF 70-300mm f/4-5.6 IS USM Lens||59.1"||(1500mm)||.25x|
|Canon EF 70-300mm f/4.5-5.6 DO IS USM Lens||55.1"||(1400mm)||.25x|
|Canon EF 75-300mm f/4-5.6 III USM Lens||59.1"||(1500mm)||.25x|
|Canon EF 100-400mm f/4.5-5.6 L IS USM Lens||70.9"||(1800mm)||.20x|
|Canon EF 300mm f/4.0 L IS USM Lens||59.1"||(1500mm)||.24x|
|Canon EF 400mm f/5.6 L USM Lens||137.8"||(3500mm)||.12x|
If you look closely at these numbers, it becomes obvious that something interesting is going on with a 300mm lens and a 200mm lens having the same MFD (Minimum Focus Distance) AND the same MM (Maximum Magnification). The primary reason for this is that the 70-300 L has a rear focusing design that results in a shortened focal length at close focus distances.
Testing shows that my 70-300 L IS will focus as close as 40.91” and 43.82” (1039mm and 1113mm) at 70mm and 300mm respectively and that the actual maximum magnification is indeed slightly higher than that of the Canon EF 70-200mm f/2.8 L IS II USM Lens. That the 70-300 L will manually focus slightly closer than it will autofocus is likely why I am seeing better results than specified.
In the end, the 70-300 L is about average in regard to maximum magnification for lenses in this class. And in this case, average is good - useful.
A floating focusing system, typically found in macro lenses, wide prime lenses and the Canon EF 85mm f/1.2 L II USM Lens, is part of the Canon EF 70-300mm f/4-5.6 L IS USM Lens design. Not found in any other telephoto zoom lenses aside from the 100-400 L as of review time, the floating focus system's purpose is to correct for aberrations at close focusing distances. While DOF becomes very shallow at MFD, the 70-300 L has very impressive image quality even at this focus distance even at 300mm and f/5.6. Here is an example:
The 100% crop image above was taken from the center vane of the top-left poinsettia leaf - very near the top edge of the full-frame 1Ds III capture. This is a location within the frame that will typically be soft at any focus distance on a lesser quality lens. The RAW image was processed with a low sharpness setting of "2" ("3" is Canon's default setting). You can see the very thin plane of sharp focus running through this cropped image.
Maximum magnification can be increased via the use of Extension Tubes. Adding the Canon EF 12mm Extension Tube II takes the MM values to 0.29-0.04x. Adding the Canon EF 25mm Extension Tube II takes the MM values to 0.38-0.09x. Telephoto lenses typically show higher MM values with a Canon 500D Close Up Lens, but the 500D is not available in 67mm filter threads at review time.
The Canon 70-300 L is officially NOT compatible with Canon extenders. This is the only Canon L zoom lens with a widest focal length of 70mm or longer that is not compatible with Canon extenders (as of review time). I've tried mounting Canon extenders to the 70-300 L - and they do not fit. The rear 70-300 L lens element physically hits the front element of the extender.
Intrigued, I did more experimenting. What I learned is that the 70-300 L's rear element retracts into the lens far enough that, at about 250mm, there is enough clearance for Canon extenders to mount.
The available with-1.4x focal length range is about 350-420mm and 500-600mm with the 2x installed. Zooming out wider than the 250mm-or-so zoom ring mark results in a physical bump inside the lens. I'm guessing that it is the rubber around the edge of the extender element contacts the rear 70-300 L lens element or its barrel. I do not recommend mounting this combination due to potential damage the to lens.
I of course felt the need to try out these unsupported combinations. My solution to the damage risk issue was to Gaffer Tape the lens zoom ring to lock it at the 300mm mark while using extenders.
Mounting a 1.4x or 2x extender behind any lens reduces its aperture range by 1 or 2 stops respectively. At review time, only Canon 1-Series bodies can autofocus when using the very-dark f/8 max aperture the 70-300 L lens and 1.4x extender combination yields. Tested 1D X and 1Ds III bodies autofocused this combination.
No bodies can AF with the even-darker f/11 max aperture the 70-300 L and 2x combo yields. While it tries, the tested 1Ds III body cannot lock focus with this combination.
The interesting part of this story starts with the fact that the Canon Extenders do not report their presence when mounted behind the 70-300 L. The reported max aperture incorrectly remains f/5.6.
And what is much more interesting is that the 70-300 L and 1.4x combination's f/8 max aperture combination autofocuses even when mounted to the 60D (and presumably on most/all other Canon EOS bodies). Autofocus speed with the 1.4x extender is very, very slow on all tested bodies, but AF does work - even on the 60D.
Since I'm sure you are wondering what the image quality from these combinations looks like, here is a look at the Canon EF 70-300 L with EF 1.4x III Extender ISO 12233 image quality. Image softening from the 1.4x is very noticeable at f/8 in mid and outer regions of the image circle, though the center of the frame remains reasonably sharp. CA becomes pronounced with increasing amounts visible toward the outer image circle. Stopping down to f/11 results in modestly better image quality.
Here is a look at the Canon EF 70-300 L with EF 2x III Extender ISO 12233 image quality. Wide open, the results with the 2x installed are remarkably close to the performance of the 1.4x III, but more sharpness/contrast degradation is apparent - especially in the center of the frame. The 1.4x III takes a wide lead in the image quality race when stopped down to the with-2x's f/11 max aperture. Diffraction levels the results from both combinations at f/16. Again, the with-2x combination has problems locking autofocus.
While the image quality of the 70-300 L with extenders is not impressive, it can certainly be usable in a pinch (especially in the center of the frame with the 1.4x).
In addition to accurate focusing, a steady camera and lens is essential for a quality image. While tripods rule, image stabilization can make a huge difference when handholding.
An extremely-useful and very-well-behaved (image does not jump around in viewfinder on startup), tripod- and monopod-sensing, 4-stop IS unit is part of the Canon EF 70-300mm f/4-5.6 L IS USM Lens package. While the 70-300 L's apertures would be considered wide/fast by few, adding a good IS system makes the lens very capable in low light situations - if the subject is not moving of course. Under good conditions (no wind and stable footing), I am finding it easy to get the rated 4 stops of help from the IS system on this lens. And I'm even seeing 5 stops of assistance at a good percentage-sharp rate.
At 70mm, my 1/8 to 1/6 sec exposures are mostly sharp and I am getting a decent percentage of good results at 1/4 sec. I even have some sharp shots with exposures as long as .8 sec. (the success rate is very low of course). At 300mm, I am getting very good results at 1/15 sec. and decent results at 1/8 sec. Again, I have some very sharp shots at even far longer exposure durations, but the keeper percentage drops off rapidly after 1/8 sec. Here is a 1/8 second example with and without image stabilization:
Above is a pair of 100% crops from full frame images shot at 300mm with a 1/8 second exposure duration. Out of 13 test shots taken at this about minus-5-stop setting, 5 of them look like this. I'm impressed.
Shooting in the wind? You will not likely be happy with your results at these test exposure durations. Wind is very destructive to image sharpness - Especially with longer focal lengths handheld. I often find myself using this lens in very strong winds - and often make this lens more aerodynamic by removing the lens hood under these conditions.
Most image stabilization systems are audible. The 70-300 L's IS makes a quiet churning sound that increases when the lens is moved rapidly. Put your ear against the lens and you will hear the sound clearly. Add a little ambient noise and you'll barely hear it from behind the viewfinder.
IS Modes 1 and 2 (panning mode) are provided.
I frequently talk about the advantages IS provides to image sharpness, but I probably do not mention enough the aid IS provides to composition. The longer the focal length you are using (the narrower the angle of view), the harder it becomes to perfectly frame your handheld shot. Having a steady viewfinder is simply a great asset in tight framing scenarios - regardless of the shutter speed/exposure duration you are shooting at.
When the Canon EF 70-300mm f/4-5.6 L IS USM Lens was announced, our only clues to the expected image quality from this lens were the red L ring, the price (high) and the MTF charts which I'll include here.
I was then encouraged by how a preproduction 70-300 L IS performed in all regards including optically. And now, with thousands of frames through production models of this lens, I am very pleased with what I'm seeing.
I purchased (retail) and tested two copies of the Canon EF 70-300mm f/4-5.6 L IS USM Lens - and their performances were essentially identical. The 70-300 L IS has very good contrast and is quite sharp wide open right into the corners of a full frame sensor. Some improvement can be seen by stopping down the aperture at the wide end of the focal length range, but at f/5.6, images are very sharp across the entire focal length range. This of course means that the 70-300 L is very sharp wide open when the max aperture becomes f/5.6 at 229mm. Here is a 300mm f/5.6 example:
The 1Ds III RAW-captured image above was processed with a sharpness setting of "2". Even with this low sharpness setting, over-sharpening can be seen in the form of aliased/jagged edges of the hairs near the dog's eye.
A very small amount of CA is visible in full frame corners at 70mm and slightly more is visible at 300mm. The 70-300 L performs quite well in this regard.
Distortion appears to be about average for a 70-300mm lens. Minor barrel distortion transitions to minor pincushion by 100mm. Pincushion distortion becomes moderate by 135mm and remains so through 300mm. Distortion will, as usual, be most obvious in pictures with straight lines running along the borders of the frame.
A rounded 8-blade aperture aids in producing good bokeh (background blur quality). I spent a good amount of time comparing bokeh between some of the zoom L lenses on this page, but did not find anything significantly different between them in the particular comparison tests I shots. Other settings being equal, a wider aperture and longer focal length will produce more background blur.
The 70-300 L IS is impressively resistant to flaring. It is best in class among all of the comparisons I've made.
Full frame format camera body owners will notice slight vignetting in the corners (nearly 1.5 stops). Stopping down one stop nearly eliminates vignetting. APS-C format (1.6x) body owners will not likely notice any vignetting even with a wide open aperture. The 70-300 L is not remarkably good or bad in this regard.
Overall, I'm very pleased with the Canon EF 70-300mm f/4-5.6 L IS USM Lens's image quality.
Canon has delivered some great telephoto L lenses in the last few years (Canon EF 70-200mm f/4.0 L IS USM Lens and Canon EF 70-200mm f/2.8 L IS II USM Lens for example), and I now add the 70-300 L IS to what I consider the "great" list. But, as I said in the beginning of this review, deciding which telephoto zoom lens is best now becomes more difficult.
There are many lenses and many lens attributes that the 70-300 L IS can be compared to, and I've had many requests for specific comparisons. I have presented some of the comparisons already in this review, and many more are available in the site's Lens Comparison Tools, but I'll include some additional guidelines and comparisons that may help in your lens purchase decision (for some, owning more than one of these lenses will make complete sense).
If you need to stop action in lower light levels or need the most background blur possible in the 70-200mm range, get one of the 70-200mm f/2.8 L Lenses.
At review time, the Canon EF 70-200mm f/2.8 L IS II USM Lens is arguably the best zoom lens available. The f/2.8 aperture will allow action to be stopped in 1/2 as much light as the 70-300 at its widest available aperture - over the entire 70-200mm focal length range. The wider aperture also allows a stronger background blur due to the reduced DOF. It is heavier and more expensive than the 70-300 L and lacks that last 100mm of focal length range. However, the non-extending 70-200 is compatible with extenders and nearly matches the 70-300 L at 280mm. The 70-200 f/2.8 IS L II holds the image quality edge, but the 70-300 L is so good that I'm not sure it matters greatly.
If you don't need IS, the Canon EF 70-200mm f/2.8 L USM Lens is a less costly alternative. The 70-300 L is sharper than the 70-200 f/2.8 wide open, but they are not greatly dissimilar at equivalent apertures. The 70-300 L has the definite advantage over this 70-200 L with a 1.4x extender at 280mm.
If you need the smallest, lightest pro-grade telephoto zoom lens available and need a fixed max aperture, get one of the 70-200mm f/4 L Lenses.
The Canon EF 70-200mm f/4.0 L IS USM Lens is one of the most impressive zoom lenses available. It is sharper than the 70-300 L wide open and has a max aperture advantage in the long end of the shared focal length range. With a 1.4x extender attached, the 70-200 f/4 IS goes to 280mm, but the 70-300 L has an image quality advantage at this length. The 70-200 f/4 IS is a smaller lens and it does not extend.
Don't need IS? The Canon EF 70-200mm f/4.0 L USM Lens is a bargain. It is a fully-pro-grade lens at a great-value price - I recommend this lens very frequently. The 70-200 f/4 has an edge in center-of-the-frame image quality, but the 70-300 L is better in the corners.
All of the 70-200 L lenses have the advantage of a fixed max aperture.
If you need the longest focal length available in a Canon zoom lens, get the Canon EF 100-400mm f/4.5-5.6 L IS USM Lens.
The Canon EF 100-400mm f/4.5-5.6 L IS USM Lens is a favorite of many, but at 12 years old upon the release of the 70-300 L, it shows its age in comparison. The 70-300 L has better image quality including better contrast/sharpness in most or all equivalent comparisons. Though the 100-400 L has fast Ring USM AF and great build quality, the 70-300 L has a smoother focus ring, a better IS system and is weather sealed. As discussed earlier in this review, the 100-400 L is larger and heavier.
One of the biggest differences is perhaps the most obvious - their focal length ranges are somewhat different. If you are photographing wildlife, the extra 100mm on the long end is going to be very welcomed. Though image quality drops noticeably with their use on the 100-400 L, extenders are compatible with this lens. If portraits are your primary use for this lens, the 70mm on the 70-300 L's wide end is probably going to be more useful to you.
If your budget does not reach the 70-300 L IS price level and the Canon EF 70-200mm f/4.0 L USM Lens is not the right lens for you, consider the Canon EF 70-300mm f/4-5.6 IS USM Lens. This is a very popular and affordable lens, but it does not offer typical L-grade build, AF performance or image quality - especially at the longer end of the focal length range. The 70-300 L IS is a much higher grade lens than the 70-300 non-L IS lens - a very nice upgrade if you own the latter.
I really like the Canon EF 70-300mm f/4.5-5.6 DO IS USM Lens with a rather big exception - its image quality. The DO is a smaller and, at review time, less expensive lens. But the 70-300 L has much better image quality - it is my definite preference.
The Canon EF 300mm f/4.0 L IS USM Lens has a 1 stop aperture advantage, less distortion and slightly better image quality at f/5.6. This comparison is of course at 300mm only. The 300 f/4 accepts extenders for optional 420 and 600mm focal lengths, but the 70-299mm range is noticeably absent. The 70-300 L is weather sealed and has a newer IS system.
The Canon EF 400mm f/5.6 L USM Lens adds to the 300 f/4 L Lens 100mm and a 1 stop reduction in max aperture. Notable is that this lens lacks IS. Weather sealing is also lacking. Otherwise, the 400 f/5.6 L is a very nice lens. It is slightly sharper than the 70-300 L at 300mm, has less distortion and accepts extenders. With extender compatibility, the 400 f/5.6 L is in a somewhat different class than the 70-300 L, though only 1-Series bodies will autofocus with the 1.4x attached and the resulting 800mm f/11 lens created by the 2x is manual focus only for all cameras.
Canon has targeted the 70-300 L IS at APS-C DSLR owners as they are often looking for lighter-weight lenses (the 70-300mm angle of view frames like a 112-480mm lens on these bodies). But, I do not yet see any reason why a full frame DSLR owner would not be just as happy with this lens.
A relatively light, very handholdable, high quality 70-300mm lens has a lot of uses. From people (including portraits) to wildlife, from landscape to sports (in decent light), from the back yard to the beach. The Canon EF 70-300mm f/4-5.6 L IS USM Lens has very good second lens, general purpose attributes.
If you are spending the time and effort to take pictures, you probably want your results to be great. With pro-grade image quality, pro-grade build quality, fast/quiet AF and excellent IS in a relatively light lens, the Canon EF 70-300mm f/4-5.6 L IS USM Lens may have your name on it. This lens has become my most-used landscape telephoto lens and has accompanied me on some of my biggest trips. I love it.