Checking of Zoom Lens

• First you should look for any scratches on the front and rear glasses against the reflection of a fluorescent lamp.



• Turn the focus and zoom ring to see if they are smooth.



• For tele-zoom, zoom to long range, then point the lens (lens mount side) to a fluorescent lamp*, look through the lens from front lens side, it should be clear, then try to focus your eyes to each lens inside to see if any scratches or dirt inside. A little fine dust should be okay in most cases.
  
  For wide-zoom, zoom to widest range, then point the lens (front lens side) to a fluorescent lamp*, look through the lens from lens mount side, it should be clear, then try to focus your eyes to each lens inside to see if any scratches or dirt inside. A little fine dust should be okay in most cases.
  
  *Caution: don't point to high intensity point source lamp, such as incandescent, halogen or compact fluorescent lamp as the strong light might hurt you eyes.



• Check the lens-release to see if it works then carefully mount the lens to a camera (use your own camera if possible, since you know your camera well), zoom to long range and look through the viewfinder to a distance object, focus the lens to see if the infinity mark aligned. Don't forget to check the image quality at the edges of your viewfinder. Focus your lens to a close object and check if the view is clear.
  
  
• Zoom to long range, fix the focus at an object, adjust the zoom from long to wide to see if the focus will change or not. As far as I know for all OM Zooms, the focus will not be changed during zooming, but for some vary-focal-length lens (like the old Vivita Series 1 28-105mm zoom), the focus will vary during zooming.
  
  
• Turn to minimum aperture, look from the lens front, release the shutter to see if the diaphragm works.