Maciej Dr�bka wrote:
> I bought a Canon EF 20-35 in mid-July and I'm very sorry to say I'm
> disappointed with the lens -- to be more exact, it's the optical quality
> that really bothers me.
> . . . .
> While the center is OK (to say the least), the
> detail in the edges is disastrous. And when I say 'edges' I mean about 30%
> towards the center from each side, . . .
> This brings me to another problem. It seems that the right side has less
> detail than the left one.
My first question is, how are you viewing the slides?
Assuming you're using a light box and loupe, then I would say that from my
experience your lens is giving abnormal results. The results I've gotten from my
20-35/3.5~4.5 have been quite satisfactory--not as good as from the 28-70L, but
as good as or better than (for example) what I get from my 28-105/3.5~4.5, and
nothing like what you describe. Indeed, what you describe sounds a lot like the
kind of thing I was getting from my slide projector until I finally found a
decent lens for it (and even now it isn't as good as I'd like). My experience
suggests that with an average scene like a landscape, you should need to look
pretty carefully to see poor resolution at the edges with this lens, and CdI's
measurements bear this out: the 20-35 measures about the same as the 28-105 at
the focal lengths they have in common and its edge resolution is rated "average"
to "good" at all focal lengths.
> Now two questions. Firstly, am I just expecting too much of a relatively
> cheap lens
>From what you describe, I would say no.
> and should I simply go for a prime if I want the optimum in
> picture quality?
If you want the best optical performance you're almost always better off with a
fixed-focal-length lens, and in most cases they have the additional advantage
that they're not wide open when shooting at f/3.5 or f/4.5, hence increasing
resolution across the frame. For example, with the 35/2 you're stopped down
quite a bit already at f/5.6, but with the 20-35, you're still close to wide
open at 35 mm and f/5.6. The 35/2 doesn't measure very well at f/2, especially
at the edges, but it measures very well--and much better than the zoom--at
f/5.6. Personally, I haven't used my 20-35 since I picked up a second-hand
24/2.8 last spring, but I haven't decided to sell the zoom since there may be
times when I want to get down to 20 mm, or to carry the 20-35, 100, and 200
rather than a combination that includes the 24 and 28-70. But if another six
months go by and I haven't used the zoom, I'll probably sell it. It's probably
worth mentioning that I rarely go as wide as 24 mm in any case--I do most of my
work at focal lengths longer than 50 mm rather than shorter, and 28 mm or 35 mm
is wide enough for me in most instances (but not all!). The point being that I
don't use either the 20-35 zoom or the 24/2.8 very often.
fcc
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