10 Tips To Test A Lens

1. Choose an appropriate lens model

Visual Examination

2. Notebook. If you have a possibility to take a laptop do it. It’s much more convenient to view pictures on it than on your camera display.
3. Checking Outside. First, examine a new lens thoroughly. There shouldn’t be any damages as scratches, chips, cracks or abrasions.
4. Checking Inside. Take off the lens covers. Also check carefully if the lenses (both front and back) have any damages. They must be transparent and safe. Then look inside the lens. Inner areas must be free of dust.

Testing the Lens

5. Checking Depth of Field. Set the lens to your camera. Set Diaphragm Priority Mode. Check the Depth of Field by closing the diaphragm step by step. In order to estimate it you can press Depth of  Field Preview button or make shots if your camera doesn’t have such a button.  
   
6. Checking Autofocus (AF). Focus different subjects at some distance from each other by turns. Focusing must be smooth without jerks or sticks.
7. Checking Manual Focus (MF) and Zoom Ring. Set the new lens at MF Mode. Focus Ring must work smoothly without almost any efforts. Requirements for Zoom Ring are the same. If there are also such switches as manual or auto modes, focus limiter and stabilization system - they also should be tested.
8. Checking Front/Back Focus. The problem can appear when you focus on a subject but the lens focuses either in front or behind the place you focused on. So you will need a tripod (you can borrow it in the shop) and a test chart (you can download it here). You may also use any newspaper with different print sizes. Put down the test chart on a plane surface and set the camera up at 45 degrees to the surface. Focus on the center line or any text fragment and make shots at min and max focal length. While examining the shots you must see the central line to be the sharpest. If the sharp zone is moved it’s better to ask for another lens.                
9. Don’t forget about packaging arrangement, documents and a warranty service coupon.

10. All testing actions are much more convenient to do at home if you ordered the lens in the internet. But the disadvantage is that they bring you only one sample. If it isn’t O.K. you’ll have to decline the purchase.