Lens Filter Thread Size: Step-Up Rings and Fit Checks

Updated October 19, 2026 · CameraGear editorial · Contains affiliate links

A screw-in filter must match the thread on the front of your lens, and that size is usually printed on the lens itself. Look for a diameter in millimeters beside the circle-and-line symbol on the front ring or the barrel. If you own lenses with different thread sizes, a step-up ring lets one larger filter fit smaller lenses, so you can buy a filter once instead of once per lens.

This guide is about sizes and fit. For the choice between filter types, see our filters explainer and screw-in versus magnetic systems.

How to find your filter thread size

The filter diameter is the diameter of the filter's male threads, according to Wikipedia's photographic filter article. The same article says the size is commonly marked on the front of the lens with the diameter symbol, so a marking such as "55 mm" with that symbol means a 55 mm filter or hood. Three places to look:

1. The front of the lens, on the ring around the glass or just inside the front rim.
2. The lens barrel or the box, where the specifications often repeat the filter size.
3. The manual or the maker's product page, under "filter diameter" or "filter size".

Write the sizes down for every lens you own. A short list in your phone settles most buying questions before you open a shop page.

Thread pitch is a second check

The thread also has a pitch, which is the spacing between ridges. Wikipedia says 0.75 mm is the most common pitch, that some makers use 1.0 mm, and that filters with different pitches are incompatible with each other's lenses. It also says a few sizes come in more than one pitch. Most lens and filter listings do not state the pitch, so the practical step is to buy a filter that names your lens or your thread size, check the return terms, and test it on the lens when it arrives.

If you cannot find a marking

Some lenses, such as ones with a rear filter slot, a bulbous front element or a built-in hood, take no screw-in filter at the front at all. Others are marked only on the lens cap, so check the cap too. If the size is not printed anywhere, search the maker's spec page by the full lens name, and avoid guessing from a similar-looking lens. A near-miss size will not screw on, and forcing it can damage the thread.

What a step-up ring does

A step-up ring screws onto the lens and has a larger thread on its outer side, so a bigger filter can attach. A filter maker's FAQ gives an example of a 77 mm filter on a 67 mm lens. You choose the ring to match both the lens size and the filter size, screw it onto the lens, and then screw the filter into the ring.

The benefit is cost and convenience. If your largest lens has the biggest thread, buy filters at that size and step each smaller lens up to it. You carry one polarizer or one neutral density filter instead of several, and you can swap it from lens to lens in the field.

The step-down trap

The same filter maker calls step-down rings less common and warns that they can cause vignetting, so use caution, especially with wide-angle lenses. Vignetting means dark corners in the image because the filter or ring blocks part of the view. The sensible rule is to buy filters for your largest lens thread and step up for the others, instead of buying a small filter and stepping down.

Hoods, caps and wide-angle lenses

Adding rings and filters changes how the front of the lens behaves. Wikipedia says that a lens hood fitted on top of one or more filters can sit far enough forward to cause vignetting, and that omitting filters may be necessary to avoid vignetting with wide-angle lenses. It also says not every filter has the thread needed for a screw-in hood, and that a clip-on hood may not attach to some filters.

From that, check four things when you add a ring and a filter:

• Hood. Does it still attach, and does it show in the corners of a wide shot?
• Lens cap. A cap that clips onto the lens barrel may not fit over a ring and filter. Check whether your cap attaches to the filter thread, and get a cap for the filter size if you need one.
• Stacking. More than one filter plus a ring adds thickness, so check wide shots for dark corners.
• Weight and stress. A large filter on a small lens sticks out further. Handle it with care, and screw it on gently and without force, as the maker advises.

If you use a variable neutral density filter, the vignette check matters more. Our article on variable versus fixed ND filters covers that choice, and our polarizer guide covers the other common filter that you might share between lenses.

A buying routine for several lenses

1. List every lens and its filter size. Note the largest one.
2. Decide which filters you want to share, such as a polarizer and a neutral density filter. UV protective filters are optional; our ND versus CPL comparison covers the two you are most likely to carry.
3. Buy those filters at the largest thread size. Leave out lenses that cannot take a filter at all, which includes some designs with a bulbous front element.
4. Buy step-up rings for each smaller lens. Match each ring to the lens thread and the filter thread.
5. Test every pairing. Attach the ring, then the filter, and take a wide shot at the widest zoom setting to look for dark corners.
6. Keep the rings with the filters. A small pouch for the rings saves hunting in a bag.

If you keep swapping filters across many lenses, a magnetic system may suit you better than a stack of rings; the screw-in versus magnetic guide linked above compares them.

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