What Is A Filter Thread?

Almost all lenses have a threaded section on the front that allows you to screw on filters to achieve certain effects.  When referring to a lens’ specifications, it should tell you the diameter of the filter thread and then you can purchase your filters in the same diameter.  Common thread sizes include 52mm, 72mm, 77mm and 82mm.  If you have a filter that you would like to use with a lens that has a different filter thread diameter, this can be achieved with a step-down ring that adapts one diameter to another.  If you do not wish to buy filters for all the different sizes of lens that you own, it is best to buy a filter to fit the largest lens, and then use these step-up rings to adapt the large filter to the smaller lenses.  You cannot really use a small filter on a lens with a larger diameter since the filter would become visible in the image.  If you already own the lens, usually the lens manufacturer will include the thread diameter on the front, as in the photo below.

If you do use a screw-on filter with your lens, you also have the choice as to whether the filter itself has a thread on it.  If you get a filter that also has a thread on it, it means you can screw a second filter on to ‘stack’ them.  The disadvantage to this is that filters that have threads on them are thicker and therefore more likely to cause vignetting at wider angles.
 

 

Additional Reading

  • What Is Vignetting?
  • What Is  A Screw-On filter?
  • What Is A Polarizing Filter?
    what is a filter thread

Thread size is usually marked on the front of the lens.  Here you see a 77mm lens and an 82mm lens.