Checking of Telephoto Lens

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



• Turn the focusing ring to see if it is smooth.



• Point the lens (lens mount side) to a fluorescent lamp*, look through the lens from the 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.
  
  *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-releaseto see if it works then carefully mount the lens to a camera (use your own camera if possible, since you know your camera well) 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 close objects and check if the view is clear.
  
  *For long telephoto lens of up to 300mm or more, the infinity mark may not be exactly aligned, but the lens should be able to focus to infinity.
  
  
• Turn to minimum aperture, look from the lens front, release the shutter to see if the diaphragm works.