I've had my Canon EF 24-70mm for about 8 years now and it's been through a lot. Lately I've noticed some internal dust and occasional focusing sounds that feel different than before. Should I get it serviced or just buy a new lens? What are the actual signs that a lens is done for?
Before dropping money on a repair or replacement, test the lens on a different camera body if you can borrow one - sometimes the focusing noise and autofocus weirdness comes from the camera's AF motor, not the lens itself. Internal dust is usually cosmetic unless you're seeing actual fungus growth or haze on the glass elements (hold it up to light to check), and a 24-70 at 8 years is still solid glass if the optics are clean. The real dealbreaker is when autofocus becomes unreliable or slow even after a good cleaning, or if you notice any grinding sounds during focusing that suggest mechanical wear inside. A service run from Canon is worth considering before you trash a lens that's probably got plenty of life left - they'll clean it out and check the mechanics for less than a new lens costs.
I've had gear sit in damp conditions and watched internal dust slowly degrade image quality over time, so I get why you're concerned. That said, internal dust alone doesn't mean it's toast - lots of lenses develop some over years of use. The real warning signs are autofocus that hunts or fails, visible fungus or heavy separation in the lens elements, optical aberrations that show up in photos (weird ghosting or loss of sharpness), or if the barrel physically feels loose.
Eight years of heavy use on a 24-70 is solid life, and getting it serviced by Canon is actually pretty reasonable before dropping cash on a new lens. The focusing sounds changing could just be the motor wearing, which they can often fix. I'd say check what a service quote runs first - if it's a couple hundred bucks you're probably good to go. If they tell you there's internal fungus or element damage, that's when you're looking at replacement instead.
Don't automatically toss it just because there's dust - that's throwing away money. The real red flags are when autofocus starts hunting constantly, if you see fungus (not just dust), or if the image gets noticeably softer even stopped down. A 24-70 from 8 years back is solid glass, so get it serviced first - Canon's repair centers can clean the internals and check the mechanics for maybe $80-150, which beats a replacement. If after servicing the focus still feels sluggish or the image quality doesn't improve, then you know it's actually dying rather than just dirty.
The focusing sounds changing is actually the thing worth paying attention to - that suggests mechanical wear in the autofocus motor or lens elements shifting slightly, which won't improve on its own. A service run can diagnose whether it's just dusty contacts (fixable and cheap) or internal damage like a worn focus ring or damaged aperture blades (where repair costs might match or exceed a used replacement). Before deciding, get a quote from Canon's service center or a reputable lens repair shop; if it's under $150-200 and the optics are still sharp in your shots, repair makes sense for an eight-year-old workhorse that clearly has sentimental value to you. The internal dust alone sits in a gray zone - some pros shoot lenses with visible dust for years without real image degradation, though it can eventually attract moisture and cause fungus, so if you live somewhere humid, that tips the scales toward servicing sooner rather than later.
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