| What
To Check For when Examining used Lenses
There has been a fair amount of discussion recently regarding
used lenses and what to check for when examining them. I thought
it might be useful to go thorugh the list of issues we've seen
in used lenses.
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- Sticky diaphragm.
I've seen this on a variety of lenses, both MF and AF. You can
spot it by flicking the diaphragm lever on the back of the lens.
The diaphragm should open and close very quickly and without any
sluggishness. Also, look for oil on the diaphragm blades. This
is often the precursor to the diaphragm getting sticky. The natural
state of a Nikon diaphragm is stopped down when the lens is removed.
Note that other brands may work differently. For example, an Olympus
OM lens opens up when removed from the camera. Ease of repairing:
easy.
-
Inability to focus to infinity or an incorrect infinity mark.
I've seen this several times and on a wide variety of lenses.
In some cases, the lens couldn't quite achieve infinity focus,
but could focus on something that was 70-80 feet away. In other
cases, the lens could focus on infinity, but the infinity point
was well beyond the infinity mark. While you can get sharp pictures
with such a lens, the distance markings and the depth of field
indicators are incorrect. This is a little more complicated to
fix, but not too big of deal. It's common with AF lenses and with
ED MF lenses for the lens to be able to focus beyond infinity.
Don't worry if you see that characteristic in your lens.
-
Sloppy zooming action. This occurs primarily with
older one-touch zooms, the most common example being the old 80-200mm
4.5. While this doesn't affect the optical performance, it can
be a nuisance. One trick you can use to improve the situation
is to apply several layers of transparent tape to the lens barrel
in the area where the zoom ring slides. When you have the right
number of layers, the zoom ring will still be easy to move, but
won't move on its own. The tape trick is easy, fixing the lens
so it's tight again is usually not economically viable.
-
Lens fungus. This shows up frequently on lenses
used in humid climates. You can see it by opening up the diaphragm,
holding the lens to a light, and looking for growths on the lens
elements that appear like faint spiderwebs. This is generally
the kiss of death for lenses. Depending on how widely spread the
fungus is, you can see a substantial loss of contrast.
-
Dented filter rings. This one is pretty obvious.
If you don't plan to use filters on the lens, it's no big deal,
but otherwise it's quite inconvenient. Sometimes a good repair
person can straighten out the filter ring and make it usable,
sometimes not.
-
Inaccurate transfer of f-stop information. I've
seen at least one AF lens that incorrectly transferred f-stop
information to the body. In the case I saw, the difference was
two f-stops. This isn't too hard to fix.
-
Small scratches or chips on front and back lens elements.
If these aren't too big, it's not a problem and you can ignore
them. Try to get a discounted price, however. Major cleaning marks
can reduce contrast and increase flare.
-
Dust inside the lens. Almost every lens has some
dust on the internal lens elements. Generally speaking, don't
worry about it. If the lens is really filthy you can have a loss
of contrast, but I haven't seen many that have that much dust.
-
Focusing and zoom rings that bind. This can occur
on both AF and MF lenses even though their internal mechanisms
are very different. A good clean, lube, and adjust will generally
fix the problem unless there is damage to the mechanism.
Incidentally,
I think used lenses are pretty low risk purchases, especially
if you know what can go wrong and how to spot it. Good hunting.
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