Essential Lens Checks Before Buying New or Used Mirrorless Glass

1. Shop from a reliable source

There’s value in buying from a seller who inspects and stands behind gear. "There’s no shortage of retailers selling second-hand lenses which is why you should be extra cautious and only buy from a reputable store that inspects and certifies their camera equipment. The seller should have put the equipment through a rigorous inspection to ensure the item you are buying is in good working order. The lens should also come with a warranty that covers parts and labor. Buying pre-owned lenses from ebay, craigslist or private seller can result in buying a subpar product." If price looks too good, factor in the lack of return window and repair cost before you click buy.

2. Inspect the physical body and mount fit

Start with the obvious but don't skip it: check for dents, loose screws, missing rubber, and a clean tripod foot. "Inspect the physical body, glass clarity, focusing/aperture mechanics, and test autofocus, sharpness, and mount fit." A play‑fit test on your camera body will catch bent mounts and electronic contact issues; mount a lens, twist it a few times, it should seat solidly without wiggle.

3. Check glass for scratches, haze, fungus, and balsam separation

Look straight through the lens into bright light and backlight it to reveal internal issues. "Fungus, haze, balsam separation, scratched front/rear elements, and stuck focusing or aperture rings lower value most quickly." "Bring a small flashlight with you, angled beams quickly reveal scratches, haze, or fungus inside the elements." Small surface dust or light, faint scratches aren’t usually deal‑killers, but deep scars or glass separations are.

4. Inspect the focusing and zoom rings, grips, and internals

Feel is as important as sight. "You want to inspect both grips on the zoom and focus rings to make sure they are intact. Next, you’ll want to confirm the rings themselves move smoothly without grinding. However, do make sure the rings are not too loose either. If the rings are too loose, this may indicate that the lens has been dropped or that there is a lot of dust and debris in the internals of the lens. To check this, move the focusing and zoom rings around, and you can tell if there is an issue rather quickly." Also cycle the zoom and AF/MF switches, they should click positively, not flop.

5. Confirm aperture mechanics and iris consistency (do this exact test)

Use this repeatable method, it catches sticky blades that kill exposure consistency. "The fol­low­ing method should work for both DSLR and mir­ror­less cameras, even those with­out a depth of field pre­view but­ton. Put the cam­era into Man­u­al Expo­sure mode, select a large f‑number and a slow shut­ter speed (some­thing like 2 to 4 sec­onds), look into the lens from the front, and press the shut­ter down to take a pic­ture. Take note of the aperture’s size during exposure, and then take sev­er­al pic­tures more. The iris should close down to the same size con­sis­tent­ly. Any devi­a­tion in aper­ture size with­out a cor­re­sponding change to the f‑number could spell trou­ble for the con­sis­ten­cy of your expo­sures." If the iris shows inconsistent movement you’ll get exposure and depth‑of‑field surprises in the field.

7. Confirm that autofocus works and watch for failure patterns

"## 9. Confirm that autofocus works", yes, test AF thoroughly. Exposuretherapy’s caution is worth repeating: "Unfor­tu­nate­ly, aut­o­fo­cus errors can occur on both DSLR and mir­ror­less cameras, even on brand-new lens­es. For exam­ple, the zoom lens I use to make these videos is my sec­ond copy. The first one had an aut­o­fo­cus so faulty that every two out of five shots were mis­fo­cused. I was lucky to notice the prob­lem before my 14-day return peri­od end­ed. Sad­ly, there’s no return pol­i­cy when buy­ing a used lens from some­one you meet on Craigslist. So don’t be shy about car­ry­ing out a thor­ough inspec­tion when buy­ing an item that’s sold “as-is.”" Practically: mount it on a body you know, shoot burst series at a high-contrast subject at typical working distances (10–20 frames per position). If you see misses approaching the "every two out of five shots" example, that’s a red flag, mills of missed frames are not “quirky,” they’re costly.

8. Test sharpness, bokeh, and focal-length behavior in the real world

"Shoot at different apertures and angles, backlight the lens to spot haze, and feel for stiff or rough movements." Don’t rely on one sample frame: compare shots wide open, stopped down one or two stops, and at different focal lengths for zooms. "Yes, provided you test systematically with good lighting and compare sharpness at various apertures and focal lengths." Also consider subjective character: "I once borrowed an older 50mm manual focus lens during a documentary shoot. Side by side with a brand-new modern equivalent, the vintage lens delivered a softer, cinematic bokeh that looked richer on portraits. That day taught me 'old' doesn’t mean 'outclassed.'"

9. Does the optical image stabilization work? (don’t skip it)

Exposuretherapy flags this explicitly: "## 13. Does the optical image stabilization work? [...]" Treat OIS as a functional system, switch stabilization on and off, then take handheld shots at slower shutter speeds (around 1/(focal length) or slower) to compare. If OIS produces blurred halves or mechanical clunks, it’s not just a cosmetic fault; repairs are expensive and common on stabilized lenses.

10. Know the common defects that drop value and how to price them

Keep this list in mind when you haggle: "Fungus, haze, balsam separation, scratched front/rear elements, and stuck focusing or aperture rings lower value most quickly." Small, faint scratches are survivable: "Also, look for scratches on the front element and rear elements of the lens. Small faint scratches are not a deal killer, but anything that has left a scar or crevices in the glass is a deal killer." Price accordingly, a lens with minor dust is different from one with balsam separation.

11. Price, replacement strategy, and the wallet math

If you’re switching systems, Samys’ reasoning nails it: "Buying lenses at almost half the retail price will make the transition a lot easier on the wallet!" Factor repair costs and the chance you’ll sell the lens later. If a reputable shop offers certification and a parts-and-labor warranty, that warranty can be worth a noticeable premium versus private‑party risk.