Jonathan Kwok wrote:
>
> (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
>
Well, Jonathan, thanks for your comprehensive assessment. That pretty
much convinces me that the f4 is the lens to get my wife. Most, if ot
all of her usage of this lens will be outside, so the 1 stop difference
shouldn't make much of a difference.
Thanks again!
Skip
--
Shadowcatcher Imagery
http://www.shadowcatcherimagery.com
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