How to Check a Used Lens for Dust, Mold, and Scratches: 5 Tips Every Photographer Should Know

Buying a used lens is a smart move—it’s a chance to get top-tier glass at a better value. But to make sure you’re getting a lens that performs as expected, it’s important to know what to look for before you buy.

Dust, mold, and scratches are the most common culprits when it comes to used lens issues. While some wear is normal, hidden damage can affect image quality, autofocus, or even the longevity of the lens itself. That’s why we’ve put together this straightforward guide to help you inspect, test, and care for your gear like a KEH Certified™ pro.

1. Know What to Look For

Even a lens that looks pristine at first glance can hide problems beneath the surface. Here’s what to focus on during your inspection:

What to Check:

• Glass Clarity: Shine a light through the lens to check for haze or internal dust.

• Mold: Look for thread-like or cloudy patterns inside the lens elements.

• Scratches: Inspect both front and rear elements for visible scuffs or marks.

• Lens Barrel: Watch for dents, cracks, or signs of impact.

• Lens Mount: Make sure the mount is clean and undamaged.

A little dust may not affect your images much, but mold spreads—and once it’s in the lens, it’s hard to get rid of. Scratches, depending on depth and location, can cause flare or reduced contrast.

2. Do a Full Physical Inspection

Grab a flashlight and take your time with this part. Use both your eyes and your hands—look for visible issues and feel for irregularities in the lens body.

Checklist:

• Exterior: Check for wear, dents, or missing parts.

• Focus and Zoom Rings: Rotate them to make sure they move smoothly.

• Lens Mount: Look for corrosion or worn metal.

Then, inspect the glass more closely. Shine your light at different angles and rotate the lens. Fine scratches or mold can be easier to spot in reflection. If you’re not sure, compare it to another lens you trust.

3. Use the Right Tools to Spot Internal Issues

Some flaws are hard to see without a little help. These simple tools can reveal more than the eye alone:

Recommended Tools:

• Flashlight: Essential for spotting internal dust or haze.

• Magnifying Glass: Helps you confirm what you’re seeing.

• UV Light: Mold sometimes fluoresces under UV, making it easier to catch.

Look for web-like mold patterns, and keep an eye out for dust that moves around when you tilt the lens. Rotate the lens under light to pick up hidden scratches.

4. Test the Lens Functionality

Mount the lens to your camera and take it for a test drive. See how it performs in real-world conditions:

Functionality Checks:

• Manual Focus: Should move smoothly from end to end.
• Autofocus: Should be quick, accurate, and quiet.
• Aperture Blades: Set the aperture to different values and check for responsiveness.
• Image Stabilization: If the lens has it, compare handheld shots with IS on and off.

Take a few test shots at different apertures and focal lengths. Zoom lenses, in particular, should perform consistently across the range.

5. Clean and Protect After Purchase

Once you’ve found a keeper, keeping it clean and stored properly will extend its life.

Cleaning Tips:

• Use a blower to remove loose dust before wiping.
• Apply lens cleaning fluid to a microfiber cloth—never directly on the glass.
• Avoid harsh cloths or tissue paper that can scratch.

Storage Tips:

• Keep lenses capped when not in use.

• Store in a dry place—add silica gel packs to control humidity.

• Regularly inspect for signs of mold or damage.

Final Thoughts

Buying a used lens doesn’t have to be risky. With a careful inspection and a little know-how, you can find high-performing gear that fits your needs—and your budget.

Whether you’re upgrading your kit or trying out a new focal length, KEH is here to help. Every KEH Certified™ lens is inspected by our expert technicians and backed by a warranty, so you can focus on the shot, not the stress.