Buying anything second hand requires a thorough examination to determine whether its worth the purchase or not. Second hand items all have a history, some better than others. You may not have a crystal ball that enables you to see the daily rundown of its past life, but you do have the item itself, and its external condition is a big indicator as far as telling the story of how it has been treated in its earlier life. This is extremely relevant with most used items, including cameras, and certainly just as important with camera lenses. This is not really a full, in-depth guide, but more of a quick advice post on what to most commonly look out for when buying second hand lenses. A lot of it is down to common sense where lens appearance is concerned.
Of course, the first one just the overall look of the lens. How worn / used does it look? Is there fading, or is it marked up quite badly. Does it have any stand-out marks, such as dents. If so, it more than likely has had quite a lot of use, and could actually be damaged in a way that could affect its image capturing capabilities.
However, while poor external cosmetic condition is generally a bad sign as far as first impressions go, and a good indicator to probably steer clear, with lenses, it does not always translate to the usability of the lens and its potential to still produce great images. Of course there are exceptions, such as dents on the filter thread (in many cases its best to steer clear of lenses with that). But as long as there is no intermittent fault and the lens glass is in great condition, there’s a very good chance that even a battered lens exterior housing can be deceptive in terms of the lens still being able to create superb quality images. I call this a sleeper glass. It looks battered and fit for the bin, but wow, the results are impeccable. So sometimes, if the price is right, it is worth the risk. Check all the vital signs and go with your instinct.
Quick Lens Scratch Test
Look through the lens while its directed at a bright light. As well as dust, if you see marks, such as scratches, depending on how long and deep they are, it would be wise to save your money and buy something else. But, if you look through the lens and see only a few very light marks, depending on what you are going to use the images for, this is still considered as acceptable. And If the price is low, it may be worth the purchase. Any scratches that are too deep will definitely affect the image quality, most the time in more ways than one.
Mould / Fungus
Also be on the lookout for lens mould / fungus. This is brought on by moisture / humidity. Easy to spot, it looks like a clouding / stringy spider-webbing (similar to a southern house spiders web) that will have formed somewhere on the lens. Again, this can affect the picture quality. But thankfully mould / fungus is not a complete deal breaker. It can be cleaned / removed. There are lots of guides and videos online that explain, in some detail, how to remove fungus from a lens. Also be on the lookout for dust.
How Are The Rings
The zoom and focus rings should be easy to turn and have no restrictions. If they are tight, or feel anything but smooth, they will more than likely need to be cleaned and this can be costly. Or, at least costly enough to not be worth the hassle. What is the condition of the rubber on the rings. Does it look like there’s plenty of life left in them, or are they in bad shape. If they are in poor condition, this is another repair job that is going to require more money out of your pocket. Unless its a top of the range lens at a real rock bottom bargain price (too good to be true perhaps), it’s probably not wise to invest in repairs / restoration when there are similar used lenses out there that can be found fairly cheap and are in near perfect condition.
Auto Focus and Manual Focus
Does the AF / MF option switch between AF and MF like its supposed to, and does this function change to each mode correctly. Bear in mid that some lens do not have an AF / MF switch, but have theirs located on the body of the camera. Some have both.
Are all the screws present, and is the lens connection thread (located at the back) in good clean condition. Is there any obvious defects or damage that will hinder a perfect connection
Auto Focus Confirmation
For this one you will need to have a camera body at hand. Test the auto focus by targeting different subjects in different locations that vary in size and distance. Is the auto focus precise when trying to laser target on certain subjects. Convinced something is wrong with your lens / camera, or just want to perform some quick tests to see if all is well with the auto focus? Take a look over at photographylife, which has a great article about how to quickly test the auto focus, and explains a little bit about different issues that can arise with auto focus in general, such as Phase Detect alignment and calibration.
Depth Of Field
Depth-of-field, or DOF as its called for short, is a little button that’s usually located near the lens that’s within finger reach when holding the camera in hand. This is mainly used for previewing the background depth of field (deep / short) / focus placement. Although not the most important function in the world for most users, the DOF should be tested, as it still has its uses. On older models it would be the shutter thread that you would need to check to make sure it is working as it should.