There are a number of physical anomalies that can be found on the optics of vintage lenses. Regardless of the abnormalities of the lens body, the critical part is the optics. Sometimes people classify lenses as “a little rough”, or “needs some attention”. These can be red flags. Note that when shopping for vintage lenses in person, take an LED flashlight along as it will help peer inside the lens to determine if it is fit for use.

① Scratches

Glass doesn’t scratch that easily, but coatings do. Scratches are easy to detect, because they usually occur on the visible, exposed glass elements. Scratches usually occur on the front or rear element of a lens. They signify obvious signs of wear, or possibly damage. Small scratches will have little effect on an image, but deep scratches will. A few small scratches on the front element will not impair performance significantly – the reason is the depth of field generally works to negate their impact. The exceptions are macro lenses and wide-angle lenses. A large number of tiny scratches may also reduce the contrast of a lens. Scratches on the rear lens will be more problematic (it is best to avoid lenses with scratched rear elements). Because there is less distance between the element and the sensor/film, most scratches will appear on the resulting picture. Deep scratches can be a sign of severe trauma. Also check for pitting. Sometimes lenses have light scratches which are caused by poor lens cleaning/polishing techniques.

② Haze or fog

Haze can be anything that settles out of the air inside the lens onto the inner surfaces of the glass. The lubricants on the aperture mechanism and in the focus threads can vaporize over time and then resettle onto the glass, and with enough time other things (dust, salt-air, fungus) can get in and collect on the glass, to the point that they are dense enough to refract the light themselves and spread it around as a “foggy” look to pictures. Haze actually gets worse with age. This may be an indication that the lens was poorly constructed, or poorly stored.

A smoky haze diffuses light equally over the entire image. This is generally caused by trillions of particles much smaller then the wavelengths of light, smearing the light over all areas equally, simply making blacks gray and reducing the overall contrast. Oily haze on the other hand has tiny droplets larger than the wavelengths of light. Because the oily haze diverts light, the haloes are much stronger and more visible.

③ Dust

Dust particles somehow get into lenses. A small bit of dust will make little or no difference to image quality. Larger specks or clumps of dust should be avoided. Check for dust by shining a light through the lens. Dust may be especially prevalent in vintage zoom lenses where the increased movement can result in dust infiltrating the inner components of the lens. So how does dust get inside the lens? Vintage lenses are not air sealed, i.e. weather sealed, meaning that air moves in and out, and of course it carries dust with it. Zoom lenses with barrels that extend out essentially “pump” air/dust into the core of the lens. In reality, small amounts of dust will impede very little of the light passing through a lens, and its impact on the image quality is minimal. Inexpensive and simple lenses can be easily disassembled and cleaned, however re-assembling the lens may again introduce dust (unless you have a clean room). Large amounts of dust may be indicative of poor long-term storage.

④ Blemishes

Many vintage lenses have lens elements that are coated with layers of some non-reflective optical material. These multicoatings minimize light reflection and the resulting lens flare and ghosting. Blemishes are regions on a lens where material has been smeared or removed by physical damage, a manufacturing defect, use of an incorrect solvent, or even being eaten away by fungus. A small blemish likely won’t affect image quality.