'Apodization' sounds like a terrible disease, but it is actually some cool technology to give us more of what we love. And the technology isn't digital, it's analogue!
The 56mm f1.2 lens for the Fujifilm X-series cameras is a portrait lens, equivalent to an 85mm mid-telephoto on a full-frame DSLR. And with a maximum aperture of f1.2, you can get some beautifully sharp portraits against some severely out-of-focus backgrounds. The 'bokeh' is beautiful.
But wait, there's more coming! The new Fujinon XF 56mmF1.2 R APD lens incorporates an apodization filter to create even more blur in your backgrounds.
Fujifilm says the apodization filter smoothes the bokeh's outlines. But it doesn't say much more!
I remember Minolta (and then Sony when Sony bought Minolta) had a 135mm soft-focus portrait lens and, as I understand it, it also used a apodization filter.
The apodization filter essentially looks like a circular graduated neutral density filter - probably better described as a 'radial' ND filter which is dark around the edges and clear in the middle. We used to use filters like this on the front of our ultra wide-angle lenses for large format photography, but this was to even out the exposure..
So what does this filter do? When a lens creates its bokeh or out-of-focus blurs, the resulting mish-mash of tones can appear a little contrasty and brighter towards the edges of the frame. The apodization filter reduces the exposure towards the edges of the frame, darkening down these areas and smoothing out the bokeh. Don't ask me more than that!
According to reading I have done (and I'm no expert), you can get a similar effect with a filter screwed onto the front of the lens, but optically you get a superior result if the filter is next to the diaphragm (aperture) itself. This is what Fujifilm has done.
The result is also similar to the gaussian blur filter you find in Photoshop and Lightroom, but of course, when you're blurring in post-production, you're blurring absolutely everything, including your subject. And masking out your subject doesn't work without a lot of extra work. In comparison, with the apodization filter in the lens, your subject remains crisp and sharp and only the background is blurred.
I haven't used the XF56mmF1.2 R APD yet, but perhaps Fujifilm will send me one to play with when they read this! I have the non-APD version of the lens and it is truly beautiful to behold!