Damaged Filter Rings

When lenses get knocked about, the filter rings are usually the part most likely to bear the brunt of the force.

If the filter ring is metal, it may become dented if the force is great. Otherwise, it will merely be scratched. But if the filter ring is made of polycarbonate, then knocking it on a hard surface will very likely crack or chip it. Sometimes, part of the filter ring may actually break off.

If you do not intend to use filters on the lens, then this is not a big issue. You can, of course, use this defect to bargain the price of the lens down. But if you intend to use filters on the lens, then you must evaluate if the damage can be repaired satisfactorily.

Dented metal filter rings can be repaired by a good service technician. Sometimes, it can be straightened out enough to fit a filter, sometimes not. It really depends on the degree of damage, and the skill of the technician. The cost of repairing it should be cheap though.

Cracked or broken polycarbonate filter rings are actually less of a problem than dented metal filter rings. You can get away with a cracked filter ring as long as you attach and remove your filters carefully. A plastic filter ring with a missing part is also not much of a problem as the remaining screw threads are often enough to hold the filter in place.

However, damaged filter rings, whether metal or polycarbonate, will likely reduce the value of the affected lenses. This is good if you can live with it because you can often use it to bargain down prices. But it also works against you if you intend to sell the same lens in the future.

Loose Switches

Many lenses have switches that control certain features of the lens. For example, the AF-M (auto-focus or manual) switch.

Used lenses may come with loose switches. So, make sure you check the switches. Make sure they can lock into place properly.

If the lens has a loose switch, check if the switch still works. It's not too bad if it's just merely loose. Certain switches (like the AF-M switch above) are unlikely to be used often. So, you can simply tape them into place.

But if you need to use the switch often or if it doesn't work at all, then you will have to send the lens in for repair. This may not cheap, so take that into consideration before buying the lens.

Dust Inside The Lens

You will probably find dust inside older lenses, especially telephoto zoom lenses and push-pull zoom lenses. You can check for it by looking through the lens at a bright source of light. You will need to flick the aperture pin to open up the aperture.

But before you check for dust inside the lens, please clean off the dust on the front and rear elements! Otherwise, you may mistaken those dust particles for dust inside the lens.

Dust near the front element are less of a problem than dust closer to the rear element. But this is normally not a problem unless there is a lot of dust. Then, you may notice a loss of contrast.

Please note that internal dust will not appear as dots on the actual picture. If you see any dots on the pictures you take, they would be from dust on the sensor.

Although it may be unsightly, dust inside the lens is not a big problem because it generally won't have an effect on the picture quality. Plus, it can be easily cleaned by a service technician. The cost of cleaning out dust from inside the lens is low and often, the technician will clean out the dust automatically whenever you send your lens for servicing.

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