(Part 2; continued over from EF 70-200 f/2.8L vs 70-200L f/4. Part 1)
Optical Performance
I have conducted systematic tests comparing both these lenses, shooting
images of my custom-designed test targets with the lenses mounted onto an
Eos 1V loaded with Velvia slide film. As with all my lens tests; mirror
lock, cable release and a solid 3-series Gitzo tripod were employed and
every frame carefully indexed. Two shots are taken at each aperture setting
to eliminate user error and slides were examined with a high quality 8x
Schneider loupe.
Optically, both lenses exhibit identical contrast and colour balance. Both
my samples produced neutral colours with only a slight hint of bluishness.
Since lens coatings and glass types are seldom identical in all production
batches, your mileage here may vary. I'd dare say that if you placed images
from both lenses side-by-side, you would not be able to tell the difference
as far as colour and contrast are concerned. Compared with the cheaper
EF70-210 f/3.5-4.5 or EF100-300 f/4.5-5.6 zooms, especially at the longer
focal lengths, both these L zooms are far superior in colour rendition,
contrast and elimination of optical abberations. Exotic glasses like ED and
flourite really make a difference in supressing abberations in lenses longer
than 90mm.
With both L lenses shot at their largest apertures, the f/4L marginally
outperforms the f/2.8L. At this setting, contrast and resolution with the
f/4L is slightly higher. Central sharpness is quite comparable but the f/4L
seems to have a slight edge here at all focal lenghts. At their max
apertures,the f/4L triumphs noticeably over the f/2.8L in its ability to
better resolve detail at the frame edges. Central sharpness with the f/2.8L
zoom set wide open is very good but the edge details are noticeably softer.
In all my tests of various units of the f2.8L zoom,(I've gone through 3
units in the past few years) I've always noticed rather severe light falloff
at all focal lengths when used wide open - I estimate about between 2/3 and
1 stop. Light fall-off resembles a darkening which is strongest at the frame
edges and gradually feathers out towards the centre.
This fall-off is completely eliminated when the lens is stopped down to
about f/4.5 or f/5.6. Rest assured however, that in actual use, you will not
normally notice this light fall-off unless your scene has a very uniform
colour, such as a large patch of blue sky stretching from corner to corner
or an evenly illuminated wall.
The f/4L zoom when shot wide open also exhibits some light fall-off in the
edges; about 1/2 stop to 2/3 stop, which is eliminated by the time you close
the aperture down to f/5.6.
Stop down the f/2.8L zoom to f/4 and it will yield marginally better results
optically compared to the f/4L zoom shot wide open. I stress the word
"marginally" since the differences are indeed very small. Closed down by
just one stop, the f/2.8L improves tremendously in its ability to resolve
fine details right to the edges. Light fall-off at the corners is equal or
less than that of the f/4L. Closed down two-stops to f/5.6, and you've
achieved the optimum performance that the f/2.8L zoom can give. By the time
you stop both lenses down to f/5.6 and f/8, you'd be hard pressed to see any
differences.
My test also indicated that at longer focal lengths of about 135mm to 200mm,
the f/2.8L version generally has higher resolution provided that you close
the lens down by at least one stop. As is typical of such zooms, both lenses
exhibit optimum optical performance when used between the extremes of both
ends - somewhere between 120mm and 150mm.
As far as distortion is concerned, both are highly corrected with some
negligible barrel distortion at the wide end which changes to minor
pincushion at the long end. The distortions are so well corrected that I
doubt you will notice it at all in normal shooting. I have used both lenses
successfully for critical architectural shots. Note that distortions DO NOT
dissipate upon stopping the lens down.
When it comes to controlling flare, both lenses do a decent job and are much
better than the EF70-210 f3.5-4.5 or the EF100-300 non L zoom. However, they
are far from perfect. I own the Leica Vario Elmar 80-200 f/4 and this lens
beats the crap out of both these L zooms when it comes to controlling flare
and ghosting. Consequently, shadow and highlight details are much better
with the Leica zoom when shooting into the light...but that's another story.
Comparing both L zooms, I would rate the f/4L version better in flare
resistance. With smaller and fewer lens elements (16 elements vs 18
elements), the f/4L is less prone to ghosting and veiled flare, but like
most Canon lenses, it will still flare if you're shooting into the sun or if
you have a strong light source just outside the frame. I'd recommend the use
of a hood at all times - they also help to protect the front elements from
rain and knocks. These telezooms flare by producing blobs of orange light
streaking through the frame, compared to heavy ghosting and green flare
blobs with the EF28-70L.
________________________________________
Please refer to Part 3 of this review.
Warm regards,
Jonathan Kwok
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