How to Check a Used Lens for Fungus, Haze, Separation and Decentering

Prepare a controlled inspection

Use a clean table, neutral background, small flashlight, blower, camera body and a detailed flat subject. Avoid touching optical surfaces and do not begin by cleaning aggressively; first document the condition as received.

Record the serial number and photograph all sides of the lens, mount, front element and rear element. This creates a reference if a return or shipping claim becomes necessary.

Start with the front and rear surfaces

Tilt each surface under reflected light. Look for cleaning marks, scratches, chips, coating damage and signs that a filter was forced or struck. Fine marks on the front element may have little visible effect, while damage near the rear element can be more consequential because it is closer to the image plane.

Examine the filter threads, front rim and mount for impact. A dented filter ring can indicate a drop even when the glass survived. A damaged mount, missing screw or uneven flange can affect alignment and communication.

Internal dust is common; patterns and density matter

Shine the light through the lens from an angle rather than staring directly into an intense beam. A few isolated particles are common in used lenses and often do not appear in photographs. Dense dust, fibers, flakes, oil droplets or debris concentrated near an optical surface deserve more attention.

Do not confuse every illuminated speck with a serious defect. Strong light makes normal dust look dramatic. The decision depends on quantity, location, pattern and whether contrast or flare changes in actual images.

Fungus often forms branching or web-like structures

Lens fungus grows when moisture and contamination create suitable conditions inside the lens. It may appear as fine branching lines, circular colonies, feathery webs or spots that expand from an edge. Advanced growth can damage coatings or glass surfaces.

A suspected fungus lens should be kept away from the normal storage cabinet until evaluated. More importantly, correct the environment: high humidity and poor ventilation threaten the rest of the equipment whether or not one lens is present.

Do not attempt deep internal cleaning as part of a return-window inspection. Sony recommends professional evaluation when fungus is suspected, and internal work can alter alignment or make a return difficult.

Haze appears as a veil and often reveals itself through flare

Haze can result from condensed lubricant, outgassing, contamination or aging materials. Under transmitted light it may look like a diffuse film rather than distinct particles. In photographs it can lower contrast, wash out shadows and create broad flare around bright light.

Compare a normal scene and a strong backlit scene. A hazy lens may look acceptable in flat light yet lose substantial contrast when the sun or a lamp enters the frame.

Separation can show rainbow edges or irregular arcs

Some optical groups use cemented elements. As the bond deteriorates, separation may begin near the edge and move inward. It can appear as iridescent bands, arcs, bubbles or a boundary that changes with viewing angle.

Separation is not the same as a simple surface smear. Repair can require separating, cleaning, recementing and realigning elements, which may exceed the value of an ordinary lens. Treat an undisclosed separation pattern as a major condition issue.

Oil and aperture problems require a functional test

Aperture blades should move promptly and consistently. On electronic lenses, mount the lens and use depth-of-field preview or make exposures at several apertures. Watch for errors, delayed movement or frames that do not change exposure as expected.

Older manual lenses may allow direct inspection of the blades. Oil can make them sluggish, but absence of visible oil does not prove perfect operation. Exercise the mechanism repeatedly without forcing it.

Focus and zoom movement reveal impact, wear and internal damage

• Rotate focus through the full range and note tight spots.
• Test autofocus near and far several times.
• Check zoom movement, lock switches and zoom creep.
• Gently test for excessive barrel or mount play.
• Confirm that extending barrels do not bind or wobble abnormally.
• Test every switch, button and control ring.

A small amount of movement can be normal in some designs. Compare with manufacturer behavior and focus on unevenness, noise, errors and changes caused by orientation.

Stabilization needs a separate check

Activate the stabilizer and compare repeated frames at slower shutter speeds. Observe the viewfinder for a controlled settling action rather than sudden jumps. Listen for abnormal grinding or repeated startup failure.

Some lenses make normal activation sounds or allow internal groups to move when unpowered. Do not diagnose a fault from sound alone. Confirm performance with the exact body and current firmware.

Decentering is an alignment problem

A decentered lens has an optical group that is not aligned as intended. The result may be one soft corner, one soft side, asymmetrical blur or a tilted plane of sharpness. Technique can imitate the same pattern, so the test must be controlled.

1. Mount the camera square to a flat, detailed target.
2. Use a tripod, electronic timer and careful focus.
3. Photograph wide open and at two smaller apertures.
4. Refocus and repeat to rule out one focus error.
5. Compare corners at equal radius from the center.
6. Rotate the setup when practical to test target alignment.

Real-world lenses are not perfectly identical in every corner. The concern is a strong, repeatable asymmetry that affects the intended use.

Test the lens at settings that expose its weaknesses

Do not use one photograph as a decentering diagnosis

Field curvature, subject depth, wind, heat shimmer, stabilization, shutter speed and slight camera tilt can create unequal corners. A reliable test repeats focus, aperture and orientation. If the soft region moves with the camera or target rather than staying with the same part of the lens image, setup error is more likely.

Very wide lenses make flat-target alignment especially demanding. When the suspected defect affects paid work, a professional optical bench or manufacturer service check is more reliable than a casual wall photograph.

Price the defect, repair risk and return rights together

A defect is not automatically a reason to reject a lens. A clearly disclosed, minor issue can be acceptable for a low-risk use at the right price. The mistake is paying normal market value while assuming that uncertain internal repair will be inexpensive.

Compare the complete package: purchase price, shipping, tax, missing hood or collar, service estimate, downtime and return rights. The lowest sticker price can be the most expensive choice when optical uncertainty is high.

Review the broader used camera lens buying guide before leaving the return window.