7Artisans has released a new 79mm split diopter filter. As with many filters, it goes on the end of your lens between the subject and the camera. This one doesn’t screw onto the lens, though. While shooting, you hold this one in front of your lens (or try to mount it to a camera cage) for maximum positional control.
The typical application of split diopters lets you film two subjects on very different focus planes while keeping them both sharp. 7Artisans, though, says that they have another less common effect. Split diopters, in bringing the plane of focus closer in the area they cover, also blur out your actual plane of focus. This lets you selectively blur parts of your image to, as 7Artisans describes it, “enhance your visual storytelling”.
Although the company says that creating two separate planes of focus in a single shot is generally the primary purpose of a split diopter, they don’t make any mention that this particular split diopter is capable of that purpose. Instead, they talk about the “silky hazy beauty” of the blur it provides. They show how it makes distracting areas of the shot more blurry to complement your overall composition, but that’s it. So, whether it can actually be used for their traditional cinematic purpose is unknown – although I suspect not. I guess we’ll have to wait for the reviews.
The diopter is available in two strengths. The +1 diopter is for use with lenses having a focal length between 50mm and 105mm. If you want to go a little wider, the +2 diopter is for use with focal lengths between 35mm and 85mm. Both diopters essentially perform the same function of throwing the part of the view that they cover out of focus. The +2 is, naturally, a little stronger than the +1.
It’s similar in technique and principle to other optical effects, such as prisms or filter systems like the Lensbaby Omni. That is, it’s putting something in front of your lens, between it and the subject, to intentionally distort how the light hits the lens and, ultimately, the sensor. It’s another creative tool that may or may not apply to the kind of shooting you do and the images you want to create.
Sample images created using this filter should give you some idea of what it does and how it can be applied to your photography.