This page is only of historical interest. Several years ago Sigma changed their distinctive matte-black lens finish, which has obvious durability problems discussed below, to a more standard black anodized-metal or black plastic finish.
Sigma EX lenses, and a few other Sigma lenses as well, are painted with a matte
black finish unlike that of any other camera lenses. The Sigma finish is more
opaque than ordinary wrinkle paint, and completely prevents any reflections from
the lens barrel. Its looks are very distinctive, because the paint contains very
small reflective specks, visible only at close range. Examined with a magnifier,
the surface of this finish looks grainy, instead of smooth. This explains its
unusual "feel" of porosity, or velvety surface, when touched.
detail of Sigma Apo EX 10-20 DGdetail of Sigma Apo EX 50-500detail of Sigma Apo EX 100-300 DG
Unfortunately, this finish has two main drawbacks. The first is that it easily
becomes dirty. Handling the lens with a slightly dusty or soiled hand, for
instance, is guaranteed to leave whitish or greyish dust prints. They can be
removed by wiping with a wet towel (of a type that does not shed dust or fibres,
or you will end up making things worse). Usually, dirt-prints cannot be removed
effectively by
wiping with a dry hand.
The second, and more important, drawback is that the
black paint ends up peeling off when the lens is handled frequently
and/or roughly. For example, my second-hand 50-500 mm came with spots on the
tripod shoe that were devoid of paint. By using my fingernails and a wood chopstick, I have been able
to peel away the black paint from most of the tripod shoe. The paint peeled off
easily in soft flakes.
peeling paint on tripod shoe (blackest areas)peeling paint on focus ring
I have seen
worn out spots on several other used Sigma lenses, so this is a frequent
occurrence. The zoom and diaphragm markings of Sigma lenses are printed, not
engraved, so if the matte finish peels off from these areas you will lose the
markings as well. In current Sigma EX lenses, the distance scale is covered by a
transparent window, so you don't have a problem here. Fortunately, in most
instances I have seen, when the paint peels off a metal surface a more durable,
standard-looking black anodized finish emerges under the paint, and the damage
is not visible from a distance. This anodized finish seems to be quite durable,
and shows no sign of wear. Plastic parts are likewise moulded in a black
material. However, I did see the shoe of a 50-500 Apo DG (of the latest variety,
with longer tripod shoe and micro-ribbed rubber rings) in which the paint peeled
off to reveal the shiny silver-coloured bare metal - so the problem can get much
worse than in my own lenses, and it can happen in the newer models as well.
I have often questioned the wisdom of Sigma in using an inferior finish on
lenses of superior mechanical and optical quality. I don't have any good
explanation of their motives. I would rather use ordinary-looking lenses with a
durable, easily cleaned finish, than unusual-looking but visibly worn-out and/or
dirty ones.
A careful examination shows that the Sigma finish has been changed at least
three times through the years. There is a finish with small reflective specks,
one with slightly larger specks, and a third with no visible specks (or extremely small
ones). The black background also differs: deep black on some lenses, greyish on
others. This suggests that Sigma has been playing with the finish, possibly
trying different formulations to make it stick better. I own a few Sigma
lenses that I purchased as new within the last year and a half, and none of them
show any peeling finish. Thus, this problem is unlikely to happen immediately after
the purchase, especially if you take good care of your lenses. Nonetheless, the
Sigma finish is definitely more delicate than the traditional black anodizing
and other types of lens finish, including the Nikkor wrinkled paint present on
larger and/or more expensive lens types. It is
possible that the Sigma finish adheres better to certain materials. Modern Sigma
lenses have external, painted parts made of plastic, aluminium alloy or
magnesium alloy (often, all three in the same lens), and it may be difficult to formulate a
paint that sticks equally well to all these materials. It is also possible that
the Sigma finish becomes softer and more easily damaged after a few years,
perhaps more so when exposed to high humidity or chemicals.
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Copyright (c) Enrico Savazzi, 1990 -
. This page was created
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