An Optical Analysis Using

In late January 2004 Canon announced two new zoom lenses, the28 – 300mm f3.5-5.6L ISand70 – 300mm f4.5-5.6 DO IS. Neither of these lenses is inexpensive. The DO lens sells for about U.S. $1,500 while the 28-300mm lens has a street price of approximately $2,400. (These are current — May, 2004 — mailorder prices).

Both lenses started shipping in late May and I had an opportunityt to use them on location photographing moose and other wildlife as well as landscape in Algonquin Park in northern Ontario. These lenses have also been subject to a bench test usingDxO Analyzer.

About Canon Lens Nomenclature

Whenever I publish a Canon lens test report I am asked the meaning of all the letters and numbers in the lens’ name. Here is a brief guide:

EF— This refers to Canon’s electronic lens mount, used in all Canon camera since 1987. The previous mechanical lens mount carried the letters FD.

28 – 70mm— this is the range of focal lengths covered by the lens, 28mm at the wide end and 70mm at the long end (for example).

f/3.5-5.6— this is the range of the maximum aperture of the lens, in this example f/3.5 at the lens’ wide angle setting, changing to f/5.6 at its longest focal length. A prime or zoom lens with a fixed maximum apeture will have just a single F stop shown in the name.

L— Canon’s designation for their top-of-the-line lenses is the letter L. These lenses are the best that the company knows how to make at any given focal length and aperture, and of course for a given price (which in the case of L series lenses is usually high).

DO— stands for Diffractive Optical and is used on Canon lenses which utlize a unique diffraction grating to control chromatic aberation and reduce lens size and weight.

IS— indicates that the lens utlizes Image Stabilzation, which reduces vibration as much as 3 stops, allowing hand holding of long lenses at much lower shutter speeds than would otherwise be possible.

USM— stands for Ultrasonic Motor, a technology that uses sound waves to position the lens elements when focusing. This reduces size, weight and power consumption of the autofocus mechanism as well as increasing speed and allowing for manual override.

An Observation on Maximum Aperture

During most of the 20th Century photographers wanted one thing above all else — faster lenses. We fought for light, spends hundreds more for an f/1.4 lens over an f/1.8. A 300mm telephoto that was faster than f/5.6 was to be coveted. Also, the quality of zoom lenses during the ’70s and ’80’s when they started to become popular wasn’t that great, and serious photographers only wanted primes. Fast ones at that.

Well, that was then and this is now. Because of advances in computer-assisted lens design and also the use of exotic glass elements, zooms lenses have become very good indeed. The best ones arealmostas good as the best primes, and much more versatile. But they are relatively slow. In fact few if any manufacturers are even producing new prime lens designs anymore, and some are even being discontinued due to slow sales. (Get ’em while you still can). New lenses like these two high-end zooms are indicative of how manufacturers are no longer fighting for speed. People would much rather have smaller, though slower lenses, not faster ones.

Why? Because digital SLRs are so much less noisy (grainy) than film was. Shooting at ISO 400 is now consideredeveryday, and if a photographer sees almost any noise at this speed they get upset. Even ISO 1200 is condidered usable. This was certainly not the case with colour transparency film (though colour neg was a bit better). In any event, no one thinks twice now about shooting at ISO 400 or higher, and so fast lenses simply aren’t as necessary for the typical photographer as they once were.

One area that has suffered though is in viewfinder brightness. Reduced frame DSLRs have dimmer viewfinders than film cameras or full-frame digital SLRs like the 1Ds, and when you combine this with a slow maximum aperture zoom the viewing can get dim indeed. Such is progress.

Canon EF 28 – 300mm f3.5-5.6L IS USM

This is a large and heavy lens at over 1.6Kg. It covers a 12X focal length range, from medium wide angle to telephoto. The lens which is finished in Canon’s off-white coloured metal has ruberized zoom and focus controls. It comes complete with a removable tripod collar, lens shade and caryying case. The closest focusing distance is a very reasonable .7 meters at all focal lengths, and it takes 77mm filters.

There are four mechnical switches on the left side of the lens for focus range limiting, AF/MF, Stabilization On and Off, and Stabilization Mode. The rear lens mount features a rubber gasket for weather sealing (as do most Canon high-end lenses over the past couple of years).

This lens utilizes a push-pull zoom design. There is a friction setting collar just behind the manual focusing ring, but I usually find that I’ve set it either too loose or too tightly. This entire design is the same as last seen on the Canon 100-400mm f/5.6L IS zoom of a few years ago. I didn’t care for it then, and I don’t care for it now.

My objections are twofold. Firstly, if the zoom friction is set so that the focal length can be set smoothly and precisely then the position creeps if the lens is tilted up or down. If it’s set so that it doesn’t creep, then it doesn’t slide smoothly enough for precise positioning without fiddling.

My second objection is that the push-pull action tends to act as a bellows, moving air around agressively inside the mirror housing, potentially stirring up dust. I have found over the past few years when using the 100-400mm zoom with digital bodies, including the D30, D60, 10D and 1Ds, that I experience noticably more dust on the sensor after using a lens with this design than with zooms that feature ring-based zooming. The lens is not compatible with Canon’s 1.4X or 2X Extenders.

In the field the lens handled well, though I really wonder at the advantage (for my uses at least) of a lens with this wide a focal length range. It really isn’t that often that one needs such a wide range of focal lengths at the same time. A wide zoom and a seperate tele zoom seem to make more sense for my purposes. When this great a range of focal lengths are needed, the size and weight can be considerations. At least with a two or three lens solution the ones not being used can be carried in a shoulder bag. Here you are forced to carry and shoot with the full and considerable weight and bulk all the time. Because of its weight and focal length (at the long end at least), this is also likely to be a tripod mounted lens much of the time for many photographers.

This test of the Canon 28 – 300mm f3.5-5.6L IS lens was conducted usingDxO Analyzer. If you are not familiar with this optical testing system please readthis tutorial. Without being familiar with how the tests are conducted, and how to read them, there’s not much point in proceeding.

The purpose of this test report is to support the empirical findings of my field test of this system. Though the tests on this page are interesting and informative (as well as accurate and repeatable), they really only tell us about selected aspects of a camera or lens’ capabilities.

In The Field

 

About The Tests

As you can see from theDxO Tutorialthere are a large number of charts and text graphs produced for each of the tests —Distortion & Chromatic Aberration,Vignetting, andBlur. (Noise is excluded here because it is only relevant to testing sensors). A more comprehensive test would have to be done at all available apertures, all available ISO speeds, and at a large cross-section of focal lengths (in the case of zoom lenses). This would not only take an inordinately large amount of time to conduct, but would take up far to much space here and likely not be of much interest.

In the case of zoom lenses this test is done at a mid-position in the lens’ focal length range. I also post data for other F stops, ISO ratings and in the case of zooms a selection of focal length, including the widest and longest. In my comments to each section I also draw attention to extremes of performance, such as maximum vignetting, greatest and least noise, etc.

To jump directly to the definition and tutorial for a specific test click on the DC, V or B logos.

Distortion and Chromatic Aberration

Canon EF 28 – 300mm f3.5-5.6L IS USM @ IS O 100.
Focal Length = 70mm

Camera used: Canon 1Ds

Distortion Distortion
@ 28mm Distortion Distortion
@ 300mm Focal Length Maximum Distortion
28mm 1.67 70mm
-0.65 300mm
-0.45

Observation

Chromatic aberration measures higher at all focal lengths than I expected from a lens in the price range. Distortion at medium and telephoto settings was moderate, but was quite strong at the wide end. It ranges from strong barell distortion at the wide end to modest pincushion distortion at the long end of its focal length range.

Vignetting

Observation

Vignetting with this lens is reasonable at both 70mm and 300mm focal lengths. At 28mm it is surprisingly high until the lens is stopped down to at least f/8. This is not a lens that I would want to use at its wide angle settings with the aperture wide open.

Blur

NB: This measurement made at F/8 to avoid maximum aperture

28mm 70mm
300mm
F/4 4.9 – – F/5.6
3.2 7.33 8.1 F/8
2.5 3.4 5 F/11
2 2.5 4.1 F/16
2.1 2.3 3.1 F/22 2.6 2.7 4.9 F/32
– 3.4 5.9

 

Observation

This is a decent performing lens when it comes to resolution, but not a great lens. The graph above shows that stopping down a couple of stops from wide open will strongly improve performance (as it does with many lenses), but at smaller apertures diffraction effects start to kill performance. F/11 and f/16 are therefore the optimum working apertures. This serves as a good example of thedarksideof using slow maximum aperture lenses. Since almost all except the very finest telephoto lenses need to be stopped down to reach their sweet spot, using a lens with a slow maximum aperture to begin with means working at small apertures, and therefore needing to use higher ISO settings. As is the case in almost every aspect of life —there’s no free lunch.

The Bottom Line

It’s big, it’s heavy and it’s expensive. All aspects of performance at the wide end of the lens’ focal range are modest, though it improves to decent levels at mid and long focal lengths. I am certain that there are photographers who will find that this lens’ performance meets their needs, and for whom its physical and financial challenges are acceptable. But for many photographers two seperate zoom lens may well prove to be a preferable solution.

Canon EF 70 – 300mm f4.5-5.6 DO IS USM

This is only the second DO lens available from Canon. The first was the controversial400mm f/4 IS DOintroduced a few years ago. When I tested that lens I was quite impressed. I saw little in the way of artifacts from the use of the then brand newDiffractive Opticstechnology. Image quality was very high, and the savings in weight and size certainly were appealing. Since then I know two active widlife and nature photographers who have used this lens extensively over at least a couple of years, and they have nothing but praise for it.

But, the DO technology remains controversial, and so when the 70 – 300mm f4.5-5.6 DO IS was announced I was very eager to try one out.

The first thing that strikes you when you first pick up this lens is how small and light it is. At 720g and less than 100mm in length when closed, you’d think you were holding an 80mm lens. The diameter is small, utilizing a 58mm filter thread. The lens’ finish is black, with the green strip first seen previously on the 400mm lens; the mark of a DO lens — the way that the red stripe is the sign of an L series lens.

Zooming is via a rotating rubberized collar close to the lens mount and because of the use of USM manual focus override can also be used at any time. On the right side of the lens is aLockswitch that secures the lens in the 70mm position to prevent it from accidently extending while being carried. Regretably, it only locks in the minimum focal length position. There are the usualImage Stabilizationswitches on the left side of the lens, for turning IS on and off and for switching IS modes. Note that this lens uses Canon’s third generation IS which does not need to be switched off when the camera is tripod mounted. The advantage of being able to turn IS off when not needed though is that it saves battery power.

Surprisingly, and unlike most recent high-end Canon lenses, this lens does not feature a rubber O ring on the lens mount. The minimum focusing distance is also a rather disappointing 1.4 meters. The lens is not compatable with Canon’s 1.4X or 2X Extenders.

This test of the 70 – 300mm f4.5-5.6 DO IS lens was conducted usingDxO Analyzer. If you are not familiar with this optical testing system please readthis tutorial. Without being familiar with how the tests are conducted, and how to read them, there’s not much point in proceeding.

The purpose of this test report is to support the empirical findings of my field test of this system. Though the tests on this page are interesting and informative (as well as accurate and repeatable), they really only tell us about selected aspects of a camera or lens’ capabilities.

In The Field

 

About The Tests

As you can see from theDxO Tutorialthere are a large number of charts and text graphs produced for each of the tests —Distortion & Chromatic Aberration,Vignetting, andBlur. (Noise is excluded here because it is only relevant to testing sensors). A more comprehensive test would have to be done at all available apertures, all available ISO speeds, and at a large cross-section of focal lengths (in the case of zoom lenses). This would not only take an inordinately large amount of time to conduct, but would take up far to much space here and likely not be of much interest.

In the case of zoom lenses this test is done at a mid-position in the lens’ focal length range. I also post data for other F stops, ISO ratings and in the case of zooms a selection of focal length, including the widest and longest. In my comments to each section I also draw attention to extremes of performance, such as maximum vignetting, greatest and least noise, etc.

To jump directly to the definition and tutorial for a specific test click on theDC,VorBlogos.

Distortion and Chromatic Aberration

Canon EF 70 – 300mm f4.5-5.6 DO IS @ ISO 100.
Focal Length = 70mm

Camera used: Canon 1Ds

Observation

Chromatic Aberation is moderate, and unlikely to be an issue on prints under most circumstances.

Vignetting

Observation

Vignetting is moderate, and not an issue except when the lens is used wide open, and even then is reasonably well controlled. Surprisingly it measures higher at 300mm wide open than at 70mm, something that is usually not the case with most zoom lenses.

Blur

70mm
300mm
F/4.5 1.95 – F/5.6
1.84 4.83 F/8
1.96 3.84 F/11
2.02 3.33 F/16
2.34 2.94 F/22 2.99 3.57 F/32
4.42 4.46

Observation

This lens measures well for blur. It is typical of a good quality medium telephoto zoom. As always the best aperture for sharpness is a couple of stops down from wide open, and at small apertures diffraction effects start to degrade image quality. F/5.6 is the best aperture when the lens is at its wide end and f/16 is the sharpest aperture at 300mm.

The Bottom Line

This is an appealing lens in many ways. It measures reasonably well, the price is acceptable for what you get, and the low weight and small size are real plusses. But I have to admit that on-screen and in prints I see a "softness" to images produced by this lens that doesn’t show up in lab measurements.

A bit of experimentation shows that it isn’t lack of resolution, but rather a slight softening of contrast as compared to non-DO lenses. I found that this is easily compensated for by using a moderate amount of additional sharpening in post-processing. With my favourite sharpening program,Photokit Sharpener, by usingEdge Sharpen 1in addition to normal Input and Output sharpening I was able to get results that are indestinguishable from those produced by a non-DO lens. I would imagine though that users who do not take the time and effort to apply appropriate sharpening to files produced by this lens may find the results a bit dissapointing. Those that do will be rewarded by crisp images and the pleasure of using a very versatile lens.