Hi
(Long) after my SMC 28-70 f/4 AL failure (rear lens elements
separation), I eventually opted for a Sigma 18-125 3.5-5.6 DC lens, that
you can find somewhere in this page:
http://www.sigmaphoto.com/lenses/lenses_all.asp
Although it is of far inferior overall optical quality, I opted for it
for the following reasons:
- Cheap and I'm not too willing to spend much for now.
- Great range for an all-purpose with a DSLR
- Read rather good reviews about optical quality (for the price).
It's a DC lens, with an image circle limited to the APS-C format, and
therefore can only be used with *ist D/DS/DL/DS2 bodies.
I've got it for about two weeks now, tried to figure out within the 7
days "free return" time, if it was worth the 290 Euros I paid for it.
Here are my comments for those interested.
The first contact is very pleasing. Although mostly polycarbonate, the
lens looks and feels very serious and well-built. Even better than my
Tokina and my AF Pentaxes. All pieces are very well adjusted, no
noticeable movements between parts. In this regard, it is better than
all my other AF lenses: Pentax 28-70 f/4, 28-80 3.5-5.6, 80-320 4.5-5.6
and Tokina AF235 19-35 3.5-4.5 included.
The zooming ring feels well, although a bit hard to my taste. The very
bad thing is that it turns the opposite way compared to all other zooms
I know. It has a small lock, that can be engaged at the 18mm setting,
and prevents the lens from extending during transport. Given the rather
stiff zooming ring, this seems not to happen anyway. Bad thing (?) is
that it can only be engaged at 18mm. I personally don't care, as the
lens stays at any set position even when held vertically!
When it extends, two cylindric sections extend from the main barrel, and
the lens becomes a 3-section telescopic tube. The first section is the
main barrel initially visible, the next one is a black metal cylinder,
the 3rd one a smaller polycarbonate black cylinder that ends with the
front lens and filter and hood mounts. This gives the whole thing a very
"telescopic" allure, a bit like some point-and-shoot ultra-zooms, and I
was quite worried that a lateral pressure at the front barrel would bend
and shake the thing, but all feels very stiff and sturdy. Even better
than my 28-70, and a lot better than the 80-320. The 3-section design,
although surprising, allows a very small size for smaller focal lengths,
and still feels serious at 125mm. At 18mm, it's about the size of the
28-80, just slightly bigger in diameter. Although the middle and end
sections are of different materials, it's noticeable only at the sound
produced by nocking both with the nail.
The focusing ring is large and comfortable. Although not exactly
"smooth", it does give some resistance in MF mode, and feels much less
"loose" than the other zooms, except maybe the 80-320. Unfortunately its
course is very short (something like 50 degrees or less!).
Unfortunately, this does not prevent the AF to be quite slow, especially
in low light. It seems that the focusing ring is too stiff, and the AF
motor struggles to move it... However, I used NiMH AA batteries, maybe
not always fully charged, and have not tried it with fresh Lithium cells
yet. But I can still say that this lens performs much less than the
28-70 in the same conditions. There is no IR focusing mark, and no
depth-of-field display.
The front lens does not move at all during focusing (no rotation, no
translation, pure internal focusing). There's a bayonet mount for a
petal-shaped hood (provided), that, as usual, can be reverse-mouted for
transport. When reverse-mounted, the zooming ring is easily accessible
even at 18mm, and the focusing ring is accessible when zooming a little
(about 30mm). So for a quick shot, this lens can be operated
out-of-the-bag with the hood reversed. I've not tried with a polarizing
filter (as I have none of this 62mm size yet), but I guess it must be
quite tricky to operate with the hood on, as there is no dedicated trap
on it.
I noticed that at wide angle, focusing quite significantly changes the
image size, as if I was zooming at the same time. It may be an
inevitable geometric effect, but I never noticed it that much with the
Tokina even at 19mm (the Tokina is not Internal Focusing, it has a fixed
filter ring, but a rotating front lens).
The hood does some obstruction to the *ist DS integrated flash at 18mm.
The focusing distance is 50cm at all focal lengths. At 125mm, this
allows a "macro" factor approx. 1/5.
One nasty detail: the *ist DS does not identify this lens. Therefore, no
lens reference at all appears in the EXIF data (which is still better
than my Tokina 19-35, that appears as a Pentax 20-35, that I wish it was!).
Of course, there is no aperture ring, as it is not intended to be used
with cameras compatible with aperture rings anyway.
Now about the image quality. I did only a few image tests, and you
probably will find much more comprehensive tests on the net or on
paper... Here is what I observed so far.
(some images visible at http://www.lacouture.nom.fr/gallery/v/Sigma-18-125/)
The vignetting is clearly visible, and does not always disappear totally
when closing one stop. Two stops usually does the job. This can be fixed
quite easily at post-processing, but be ready for it.
One impressive thing is that this lens is almost completely immune to
purple/blue fringing. There IS some at the very corners, but it's so
limited. Nothing comparable with the Tokina at 19mm!
I found it pretty sharp at the center, and acceptable in corners when
stopping down a little.
The flare was reasonable, but dirt on the front lens sometimes generates
ugly things when hit by the sun.
The distortions are quite noticeable, too, but PTLens does a good job
fixing that when required.
In short, this lens seems to be able to produce decent pictures,
provided that you dot not furiously want to autofocus in low-light
environment. It is small and very convenient for day-to-day usage.
Obviously its range gives it impressive versatility.
For more elaborated work, keep other, more specialized lenses if you
have or can afford them. I would definitely rather use my M-135 f/3.5
for sustained or critical work at the long end. I've not compared images
side by side with the Tokina 19-35 yet, and my 28-70 is dead.
Or be prepared to do some post-processing, or to trade one or two stops.
If you want a versatile lens for everyday use, and do not have much more
than 300 euros to spend on it, I believe you can't get anything better
than this.
There's been discussion about rather buying the Sigma 18-200 instead of
this 18-125. I like the 50-125 focals (APS-C focal lengths), but very
seldom use longer lengths (I can't hold these very well anyway). 18-125
with one lens is very convenient in 95% of my time, and occasionally
switching to a 80-320 or a fixed 135mm (which I both already had) seems
reasonable to me.
This was only my 2 cents.
Best regards
Patrice
