What Is Lens Filter Thread Size and Why Does It Matter?

If you have looked at a camera lens and seen markings such as 49mm, 52mm, 58mm or 67mm, that number is often the filter thread size. It matters when you want to attach a screw-in filter or another compatible front accessory.

What is filter thread size?

Filter thread size is the diameter of the threaded section at the front of a compatible lens, usually measured in millimetres. A lens marked 58mm is designed to accept compatible 58mm screw-in filters.

Why can two lenses have different filter sizes?

Filter size is a physical lens specification and can vary between lenses even when their focal lengths are similar. Front-element design, barrel size and optical construction can all affect the required filter diameter.

What happens if your filter size is different?

A filter that is smaller than the lens thread will not screw directly onto it. Step-up or step-down rings can sometimes be used, but the ring and filter must be compatible with the lens and intended setup.

How to find your lens filter size

• Check the marking around the front of the lens.

• Look for the diameter symbol followed by a number, such as Ø58.

• Check the lens specifications if the front marking is difficult to read.

What should you check when buying a used lens?

If you already own filters, check the used lens's filter thread size before buying. Also inspect the front thread for damage, dents or cross-threading and make sure a filter or lens cap can be fitted normally.

Filter thread size is a small specification, but checking it before buying can save you from ordering the wrong filter or discovering that an accessory you already own does not fit directly.