What is Apodization?

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Not exactly a brand-new technology, apodization has taken off in recent years, with major manufacturers releasing new lenses that use the fancy filters. A relatively simple idea, apodization works without all that much tech behind it. However, it gets tough to explain the effects and potential drawbacks to these optics. Basically, it’s all in the name of good bokeh.

What is an Apodization Filter?

In the simplest terms, an apodization filter is a radial graduated neutral density filter, and it’s usually concave. In layman’s terms, this means that the very center of the filter is clear and it gets progressively darker as you move toward the edges. You will also find it tucked away inside the optical design. It isn’t simply another filter you can slap on the front of your lens and call it a day. This means that in a well-designed lens, the element should not have an impact on overall image quality—your images will still be tack sharp—though it will affect the lens’s light-gathering capabilities.

Manufacturers understand that the discrepancy between the aperture and actual transmission can be confusing, which is why many opt for a double aperture ring of sorts, with two sets of numbers. One is the physical aperture. The use of an apodization filter does not affect this figure, so an f/2 lens is still an f/2 lens, especially when you are calculating depth of field. The other set of numbers is the T-stop, or transmission stop. More commonly found in video/film applications, the T-stop refers to the actual transmission of the lens and is used to calculate exposure. An interesting tidbit is that since the apodization filter is most effective toward the edges of the lens, when you stop down, the difference between the f-stop and T-stop will lessen and, in some instances, disappear.

If you want to see some apodization lenses in action, you should view this video, produced by the B&H Online Videos team!

If you want to begin your search for an apodization lens, you should know there are multiple terms out there, much like the way there are various names for image stabilizers and autofocus motors. Fortunately, companies have been direct about whether their lenses use an apodization filter, although Sony and Venus Optics opt for the term Smooth Trans Focus, or STF, while Fujifilm uses the simple “APD” designation. Canon has also announced the development of a Defocus Smoothing, or DS, lens, which I would assume at this point refers to an apodization element, though we can’t be 100% sure until the official launch. Basically, do your research, and note that some manufacturers produce the same lens both with and without the apodization element.

The Effect

What exactly is better bokeh? Great question, though I think if you went with smoother and rounder, most photographers would agree. Standard optics can fall victim to undesired flaws in the bokeh they render. Cat-eye bokeh, onion rings, and polygonal bokeh are good examples. Apodization filters can correct for many of these issues when combined with the proper optics. As the filter darkens as you move toward the edges, it will soften the edges of the bokeh. In many instances, this results in the bokeh “balls” slowly fading out and, since the filter is circular, it can help ensure that the bokeh remains circular.

When you look at a lens with standard bokeh, you will have a hard edge on any bokeh circles. These circles aren’t always circles, either. Sometimes a lens will produce oval shapes, or you can clearly make out the aperture blades if you stop down. Apodization changes that, for better and worse. Sometimes the distinct look of a lens and its bokeh can be attractive. For example, so-called cat-eye bokeh around the edges of the frame can mean that the lens will create a swirling effect around the edges in out-of-focus areas and, for some photographers, this may be a desired look. Apodization has its own distinct look that will be loved by some and hated by others.

Bokeh becomes ultra-smooth when an apodization element is used. Bokeh is about the out-of-focus elements of an image, and smoother bokeh is generally considered better. That is the goal of apodization and it is very successful. Point light sources that are out of focus slowly fade out from their centers, matching the look of the apodization filter. For everything else, it just turns into a smooth blur, especially in distant backgrounds. It is beautiful and not distracting, very helpful when you want to draw attention solely to your subject. This is what makes apodization lenses appealing for portraiture, because they ensure that your photos highlight the individual in the image and reduce the impact of any foreground or background elements.

There are a few options on the market today that feature apodization technology. Sony offers the FE 100mm f/2.8 STF GM OSS for full-frame E-mount cameras, where it benefits from full autofocus support. Sony A-mount shooters can pick up the 135mm f/2.8 STF, with its manual focus design and, interestingly, two aperture diaphragms. Fujifilm offers its XF 56mm f/1.2 R lens in an APD version and, for DSLR fans, Venus Optics has you covered with the Laowa 105mm f/2 Smooth Trans Focus Lens in Canon EF, Nikon F, Pentax K, and Sony A.

Sony FE 100mm f/2.8 STF GM OSS Lens

Intrigued by the advantages of an apodization lens? Looking to add one to your kit? Sound off in the Comments section with any thoughts or experience you have with apodization optics!

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