SLR Photo lenses are expensive. Good SLR lenses are very expensive, often exceeding the price of a mid-range Canon or Nikon DSLR camera itself. As I’m about to get a used L-series Canon EF Lens, I thought I’d share with you a checklist that I prepared to help me remember (and guide me on) what to check before buying. This is, by no means, a comprehensive guide or checklist, but rather an assortment of advice I’ve gathered from friends and by reading articles and comments in online forums.
You will need:
- Your SLR (or DSLR) camera
- A lint-free lens cloth or pen
- A rubber blower (not compressed air)
- A light source (a bright sky or well-lit white wall is just fine)
- Patience
Check the contents
Common sense stuff first. Lenses always come with a manual and a box. Ask for them. Ask for the warranty, if any. Also make sure the lens has its front and rear lens caps attached and that they are intact. Spare lens caps are not always easy to find. Good lenses typically come with a hood (cheaper ones usually don’t, but you can buy the hood for most lenses relatively cheaply). If you know that the lens you’re buying comes with a hood, ask for it too.
A First look
After checking the contents of the box and associated accessories of the lens, you should visually inspect the lens:
- Check for dents
- Check for deep scratches
- Check for marks on screws that might indicate a botched repair
- Check the electric switches (focus, stabiliser, focusing distance and others). They should not be loose. If they are check whether they function as intended. In general avoid getting a lens with loose switches.
- Check the Zoom and Focus Rings. Their motion should be smooth. It should not be tight or gritty. Tight or gritty motion might require cleaning or lubrication (servicing of the lens).
- Check the Zoom action. The Zoom ring should not be loose in any way. Turn the zoom ring all the way and observe the zoom range.
- Check the Filter Ring at the front of the lens. The ring can be metallic or plastic (polycarbonate). If it is made of metal, it might be bent as a result of excessive force or a dropped lens. Bent filter rings can — sometimes — be repaired; if it is a polycarbonate ring, check it carefully for cracks or broken pieces. If you use filters (most photographers occasionally use a filter, even if it is merely for protecting the lens) you’ll probably want a lens without a broken or bent filter ring.
Inside the Lens & Lens Elements
There are several aspects of the lens elements that require attention. The procedure for checking the elements is somewhat similar, no matter what you’re looking for. When you wish to check the elements themselves, set the aperture wide-open and look through the lens with a bright light facing it. Before examining the elements or the interior of the lens, make sure you clean the front and rear glasses with a blower and a lint-free lens cloth.
Dust
Check for dust inside the lens. While shining light through the lens, move the lens back and forth and focus on the different elements whilst looking for dust inside. A small amount of dust may be acceptable.
Aperture Blades
There are two main possible problems with aperture blades. Oil on the blades and their response. The two may — in some cases — be related.
- Stop-down the lens. Observe the lens whilst pressing the DOF button on your SLR. The blades should appear very quickly and their motion should be uniform. Observe the blades. There should not be any oil stains on the blades.
- With the lens stopped-down again, look through the viewfinder and point the camera to a bright object (white lit wall, sky etc.). Press the DOF button. The viewfinder should darken instantaneously, you should hear the blades snapping into place. The dark regions should be uniform.
Elements
Check the front an back elements for scratches, chipping, fungus, etched fingerprints. Also check the coatings. For all those take a RAW or high-quality JPEG image with the camera and — after transferring it to a computer — examine it at 100%.
Remove the lens from the camera and point it to a bright light source. Focus on the different elements inside the lens and look for discolouration in regions of the lens. This indicates that the lens elements have separated. This repair is extremely costly and typically lenses with separated elements are discarded.
Gently shake the lens and look/listen for rattling. This indicates one or more loose elements. A single loose element might be acceptable; multiple loose elements will most certainly affect the focusing operation of the lens. Taking pictures of objects at differing distances (in good light) is essential to ensuring that the lens works as intended.
Autofocus
The lens — if an autofocus — should focus quickly no matter what the distance of the object. Pay special attention to objects located very far away as loose elements will prevent the lens from focusing on objects at infinity. Take several shots; the lens should focus quickly and silently.
Remember: Test that Lens!
In general, it is essential to ensure that a lens works before purchase and that it is covered with warranty if the above checks cannot be performed. Testing a lens does not take a long time and can help you avoid a lot of grief later. If getting it from a store ask about their return policy. Reputable stores will typically offer a money-back guarantee for the first few weeks after the sale.
Some friends have asked me about getting second hand lenses online. Getting AF lenses online is quite risky in my opinion, even from respectable stores (that test the lenses for you). I wouldn’t do it as I’ve got no way to examine the lens before purchasing.
Lenses are — generally — good investments if you make sure you use and store them carefully. You can find pretty decent second-hand high-quality lenses for cheap if you look around. Just make sure you test the lens before purchasing. Good luck!