Canon EF 70-300mm f4.5-5.6 DO IS USM lens test
by David Hay
Why I wanted one.
As a long-term user of a Canon 75-300 IS USM lens I hoped that Canon would
bring out an L-series version of this lens with better optical quality,
especially at the 300mm end. When Canon introduced the 100-400 IS lens I bought
one to get higher quality images of wildlife at long focal lengths but although
the results were good, I found the lens very heavy to use and only carried it on
specific projects. Most times I just carried the 75-300 IS as it fitted into my
small bag , was much lighter to hand-hold, and on my Canon 10D was equivalent to
120-480mm.
When Canon announced the EF 70-300 DO lens at just under 10cm in length, this
sounded like the lens for me. It was described as of near L-series quality and
the MTF tests published showed good performance at 300mm, the focal length I use
most often. I placed an order immediately with a friend who is a photo
dealer.
100-400L IS, 75-300 IS and 70-300 DO IS compared at wide setting
100-400L IS, 75-300 IS and 70-300 DO IS at 300mm setting
What happened to ‘delivery starts end March/early April’
Two or three months later, at the opening of a photographic exhibition in May
my friend the photo dealer said “Your lens came in a couple of days ago, I
tried to drop it off at your house but there was no-one in”. The next
night, after the shop closed he delivered the lens just in time for a trip the
following day to the Outer Hebrides, islands of the west coast of Scotland.
Opening the box
First impressions of the lens were good, the build quality was substantial,
the lens was certainly short, fatter than I expected and also quite heavy. It
came with a lens hood, almost as big as the lens itself, and a soft case.
Although only slightly heavier than the 75-300, it felt substantially heavier,
probably because of the small size. Focussing was much faster (and quieter) than
the 75-300, almost up to the 100-400 standard. Full-time manual focus was
available, unlike the 75-300 and the front of the lens did not rotate during
focussing. Switching on the Image Stabiliser was a revelation. The image became
very stable in the viewfinder, noticeably better than the 75-300. The
3rd generation 3-stop advantage stabiliser looked promising.
The zoom control is at the back of the lens so is rather close to the body.
The zooming action is quite heavy and alters depending on whether the lens is
pointing up or down. Looking down on subjects from a cliff top I noticed that
zooming back from 300 to 70mm was quite difficult. Although the lens slides out
to 300mm when pointed down, a lock is available to keep it at 70mm during travel.
I kept forgetting I had engaged the lock and wondered why I couldn’t zoom
out when a bird flew past.
I was surprised to actually see a series of concentric circles when looking
through the lens from the rear. Could the diffractive optics produce high quality
images without any optical side-effects?
How do diffractive optics work?
Diffraction is normally viewed as a problem in photographic lenses, causing
light scatter at small apertures. Canon is the first, and so far the only, lens
manufacturer to use diffractive optics to focus light. The diffractive element
contains embedded optical plastic parts with a series of moulded concentric rings
which bend light more steeply than conventional refractive lenses. The first DO
lens produced, the 400 DO, had two of these but for a zoom lens, where the angle
of light passing through varies with focal length, a third was needed with an air
space. A major advantage of a DO lens group is that chromatic aberration is
reversed compared with normal refractive elements so by combining both types,
chromatic aberration, the major cause of loss of sharpness at long focal lengths,
can be almost cancelled out.
What was the optical performance like in real life photographic situations? In
bright light, with the sun above or to the rear, sharpness and colour saturation
were good, even at full aperture. On a variety of subjects the fine detail
revealed after light USM (200%, 0.3 pixels) was impressive. However I soon
started to notice a dreamy quality to some of the photos, especially around white
subjects, when photographing into the light. Even using the lens hood I got
substantial multi-coloured flare when photographing into low light when the light
source was just out of the frame. Highlights from water revealed obvious
target-shaped discs. When I used a mirror lens many years ago I got to like the
doughnut shaped out-of-focus effects and often framed pictures to maximise the
effect. I found myself doing the same thing with this lens when photographing a
sea bird colony. Out of focus areas also had a ‘broken’ quality with
leaves sub-divided and fine details like grasses repeated.
So the lens is capable of high quality results in most lighting conditions but
in back-lit situations, which I do a lot of, light scatter within the lens,
almost certainly from the diffractive group, can lead to variable loss of
quality. Heavier than normal Unsharp Masking can improve some of this as it
increases the contrast at edges, where this dreamy quality is most obvious, but
this should not be necessary in a £1,000 lens.
The focussing and image stabiliser performance was impressive. I took a series
of shots of sea birds in (rapid) flight on a windy day on a cliff top. Using the
Sport mode on the 10D the focus appeared to be able to stay with the bird, after
the middle target locked on, even when the bird came straight towards me. The hit
rate of the final images was even higher than it looked through the viewfinder as
the lens kept tracking the birds during the exposure.
Verdict?
The pros and cons of the 3 lenses are as follows :-
75-300 IS
Pros
- Cheap
- Good quality up to 200mm, OK at 300mm at f8-11 with the stabiliser on.
- Light
CONS
- Slooooow focus, no good for birds in flight
- Rotating front
- No full-time manual focus
70-300 DO IS
PROS
- Short
- Fast focus, good enough for birds in flight
- Excellent stabiliser
CONS
- Too expensive
- Internal light scatter
- Target shaped highlights?
100-400 IS
PROS
- L-series build quality
- Usable at all focal
lengths
- Good stabiliser
- Fast focus
CONS
- Expensive but good value
- Very heavy, tiring to hand
hold, you need the stabiliser when your arms start to shake!
- Push-pull zoom
Would I recommend the 70-300
DO?
It is probably not for most
people, especially at the price. Here in the UK it sells for £1,049. Canon
have to recover the R+D costs of diffractive optics so early products will carry
a premium price. They see the technology coming to cheaper lenses eventually,
allowing shorter low-cost lenses to be produced. The cost of moulding diffractive
elements, if mass-produced, is said not to be inherently high.
The main benefit of the DO
optics in the 70-300 is the reduction in length (but not weight). A short lens
has obvious attractions for candid photography. After my experiences with flare I
started using the lens hood all the time, but guess what, the 70-300 with lens
hood attached is the same length as the 75-300 without one! No gain there
then.
Also the penalty of variable
quality loss when photographing white subjects and into the light still causes me
concern. When looking through the back of the lens around 50 concentric circles
are visible in the diffractive optic. They show up as white when light shines on
them. It looks like these are causing the effects noted at full aperture with
additional white stray light affecting the image. However because the circles are
much closer together towards the edge of the lens, most willbe masked off quickly
as the lens is stopped down. This would lead to the obvious improvement in
quality seen at smaller apertures.
L-series photographers will
probably not be satisfied with the quality of this lens but creative
photographers may have fun exploring the unique visual effects that this lens can
produce. Me, I am still waiting for a 75-300 L-series lens that can produce a
high quality image at full aperture at 300mm.
The caveat, as always, is that
this is a test of only one lens, and an really early one at that (No. 88000244).
If Canon think that it is not representative of the current production, I would
be happy to test another example and publish the results, (provided I can keep
the best one).
Sample Images
Comparison images of shots taken
with the 100-400, 75-300 and 70-300 lenses will hopefully be the subject of a
future article, but here is one shot which shows the excellent supression of the
70-300DO IS lens compared to the 75-300 IS. This is a crop taken from a section
towards the edge of the frame. On the left is the image from the 70-300DI IS and
on the right is the image from the 75-300 IS. It's pretty clear that the
chromatic abrerration seen in the 75-300 shot is gone in the 70-300DO
shot.
The following images were all
shot with the 70-300 DO IS lens:
In the image below (full frame)
you can see excellent sharpness at 300mm and full aperture (f5.6), even with an
off center subject
However in the 100% crop from
the original image shown below you can see a faint white halo around the
wire.
Backlit flowers - In the image
below you can see a strong colored flare despite lens hood use and sun not in
frame.
Below is the same shot but with
a hand used to shade the front element from direct sunlight. A dramatic reduction
in flare is seen.
Herring gull - This 100% crop
from a full frame shots shown an example of target-shaped out-of-focus
highlights
North Uist landscape - excellent
detail at 100mm with polariser.
Kitiwake - Good detail in 100%
crop. No halo around white 1/2 stop down from wide open (f6.7).
Starling 100% crop - Good
sharpness with black subject
Starlings - Good sharpness with
black subject
Where to
buy
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© Copyright 2004 David
Hay
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, June 19, 2004; 12:46 A.M. 
