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what size nd filter do i need

If you’re looking to buy filters, lens caps, or hoods, you need to know the diameter of your lens. But you don’t need to break out a ruler. You just need to know the code.

Lens Diameter vs Focal Length vs Aperture

The lens diameter isn’t the same thing as saying a 50mm lens or a 70-200mm lens-that’s the focal length. Nor does it have anything to do with aperture settings like f/1.8 or f/5.6.

Lens diameter is the physical measurement of the diameter of the front-most part of the lens. With DSLR lenses, it’s often threaded to allow filters and lens hoods to screw in. On mirrorless and Micro Four Thirds lenses, some have threads for filters, and some don’t.

If you have a DSLR lens with a focal length of 50mm, it doesn’t mean you’d use a 50mm filter-they’re referring to two different measurements.

Some of the common sizes for the diameter of DSLR lenses are 43mm, 49mm, 52mm, 44mm, 58mm, 62mm, 68mm, 72mm, and 77mm. A 77mm filter won’t fit on a lens with a 72mm lens diameter (you can sometimes use an adapter, but that introduces other problems).

How to Find the Lens Diameter

But so long as you know what to look for, it’s usually easy to find out because it’s often printed right there on the lens. It might not be easy to spot because, on some lenses, it’s etched into the plastic or metal and not easy to see, but there’s a good chance it’s there. It’s one of the few standards that camera manufacturers stick to. So whether it’s a Nikon lens, a Canon lens, a Sigma lens, or so on, the lens diameter is marked the same way.

There’s a code, but it’s a simple one. And once you know what to look for, it’s easy.

What you’re looking for is something using the geometric symbol for diameter: ø. So, for example, if you see ø52, the lens has a diameter of 52mm, so you’d look for a 52mm filter. Or if you see ø77 it’s a 77mm diameter. And so on.

Lens Diameter Examples

Here are some examples of what you’re looking for. In these cases, it’s clearly marked in white text. Some manufacturers aren’t quite so considerate, though; sometimes you have to look for lightly etched numbers. Sometimes it’s on the outside of the lens, and sometimes it’s just inside the rim. Occasionally a lens won’t have it marked, in which case your best bet is either trial and error or trying to track down a copy of the user manual or lens specs on the manufacturer’s website (or try the lens filter size charts below).

This one takes 72mm filters. Lens Diameter Example

And this one takes 58mm filters. Lens Diameter Example

If Your Lens Doesn’t Have the Lens Diameter Marked

Some lenses don’t have the lens diameter marked on them. In those cases, it’s time to break out a ruler with millimeters marked on it. Or, better yet, some calipers.

What you want to measure is the distance across the widest part of the lens (i.e., going through the middle of the circle) starting from the inside rim of the threaded area on one side to the inside rim of the thread on the other side. That then provides the maximum diameter of a filter that will screw into that thread.

Because it’s a rather imprecise way of doing it, here are some common diameters used in DSLR lenses (all are in millimeters): 37, 39, 40, 40.5, 43, 46, 49, 52, 55, 58, 60, 62, 67, 72, 77, 82, 86, 95.

Of those, the ones between 49mm and 77mm tend to be most common for DSLR lenses. If you end up with a measurement for a size that you can’t find a filter for, chances are the measurement is a touch off. The major filter manufacturers don’t make a 50mm filter size, for example, so in that case, you’re probably actually after a 49mm filter.

If Your Lens Doesn’t Have a Filter Thread

Most DSLR lenses have filter threads, but not all of them. Some lenses, especially on the cheap end of the market, just aren’t designed for them. But even very expensive specialty lenses can lack a filter thread. Some of them, like extreme wide-angles or fisheyes, often have a very curved front element that doesn’t allow a flat filter. Others, like very long telephoto lenses, might have a very large front element that makes a filter impractical. In some cases, they’ll take filters on the other end of the lens at the mount point.

If your lens doesn’t have that option and you still want to use filters, a filter holder system like the Cokin filter system is worth looking into. Some of the holders still attach to a lens’s filter thread, but some can be mounted on the outside of a lens. They hold larger glass or polycarbonate filters in place. These filters are often rectangular or square. While they’re less convenient and more cumbersome to use, they’re especially popular for landscape photographers who have the luxury of very deliberate shooting, in part because you can stack multiple filters for different effects, you can get very high-quality filters with a huge range of different types and effects, and the design is especially well-suited to being able to precisely align graduated neutral-density filters (to darken a bright sky, for example).

Things to Watch For

There are a few things to bear in mind when buying screw-in filters for lenses.

  • While the threads are mostly quite standardized, it is possible to come across outliers with a slightly modified thread. It’s also possible to damage the thread from over-tightening the filter. Plastic threads are especially vulnerable to damage, but some lenses also use a softer metal that is quite easy to damage.
  • A common issue with adding screw-in filters is getting vignetting at the corners and edges of the frame. It’s especially likely when stacking two or more filters on top of each other, so it’s often a good idea to keep the number of stacked filters to a minimum. With wide-angle lenses, slim-profile polarizer filters can be a good option to reduce the risk of vignetting.
  • Screw-in filters don’t always work well with lens hoods. That’s especially true of circular polarizers, where you need to rotate the filter to get the proper polarizing effect.
  • Many filters have a coating applied to reduce glare.

Lens Filter Size Charts

I’ve compiled some lens filter size charts, starting with some of the most commonly used and current lenses. You can find the corresponding chart here:

  • Canon lens filter sizes
  • Nikon lens filter sizes
  • Sony lens filter sizes
  • Fujifilm / Fujinon lens filter sizes
  • Olympus lens filter sizes
  • Pentax lens filter sizes
  • Sigma lens filter sizes
  • Tamron lens filter sizes

Things Worth Knowing About Lens Diameter

Does the diameter of a lens matter?

The larger the opening, the more light that can enter, and the larger the lens elements that can be used internally. Those can potentially contribute to better optical quality, with potentially less light fall-off at the edges (vignetting) and potentially sharper images at wide apertures. You’ll notice in the tables above that the more expensive “pro-level” lenses tend to have larger lens diameters than less-expensive consumer versions at the same focal lengths.

But there’s a reason I keep saying “potentially,” and that’s because you can’t tell the quality of a lens from its lens diameter. There are many other aspects that contribute to a lens’s quality, including its optical design, the type and quality of the glass, and the manufacturing precision.

Wide-angle and long telephoto lenses also tend to have larger lens diameters, the former to allow a wider perspective of the scene and the latter to allow in more light.

A further complication is that lenses are designed for particular sensors. Because full-frame sensors are obviously larger than cropped APS-C sensors, the lenses that are designed for full-frame cameras tend to have larger lens diameters than their equivalents designed to go on cropped-sensor bodies. Lenses for smaller sensors, like Micro Four Thirds, are typically smaller still.

So, in short, yes, the diameter of a lens does matter in the sense that it’s an important part of the optical design of a lens. But you can’t look at the lens diameter and determine the quality of a lens, and it’s not really a spec that is worth factoring into the decision on which to buy.

What size filter will fit my lens?

The first thing to determine is whether your lens has a filter thread on the front. While many lenses do, there are also more than a few that don’t.

If your lens has a filter thread, you’ll need to find out the lens diameter. In many cases, it’s marked on the lens itself with the ø followed by a number. That refers to millimeters. So ø58, for instance, would mean it will take 58mm screw-in filters.

If your lens doesn’t have a filter thread, it doesn’t necessarily mean there’s no way to use a filter. In some cases, a filter mount system might be a good option (there’s more about those above). In a few cases, the camera manufacturer might have released a dedicated filter to attach to the lens/camera combination (GoPro cameras are a good example of this because they use a non-standard lens port).

How do you remove a filter that’s stuck on a lens?

Sometimes filters can become stuck on a lens. It might be screwed on too tightly, or salt spray or grit might be jammed in the filter thread. And because the filters are so thin, there’s often not much opportunity to get a good grip with your bare hands. Especially if your hands are cold or wet (or both), which is common in landscape photography.

Two quick options are to use a clean cloth to try to get a better grip. I find that a rubber band wrapped around the filter works even better.

If you find yourself putting filters on and off a lot, you can also get inexpensive filter wrenches that are an elegant solution that have the benefit of reducing the risk of getting fingerprints on the filter or lens’s front element. They’re especially useful when your hands are cold or wet.

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