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Apodization filters seem to be used to improve bokeh. They also seem to be able to improve sharpness and increase depth of field. But they also reduce light transmission.

While thinking about how an adjustable apodization filter could be made, I thought about translucent aperture blades. Could they have benefits similar to apodization filters (improving bokeh)? What else might be expected to happen if a lens had translucent aperture blades?

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An apodization filter improves bokeh and sharpness by blocking some of the light coming from the periphery of the objective lens which are prone to greater lens errors. This is effectively the same as how stopping down can improve sharpness and bokeh characteristics.

Translucent aperture blades would be the opposite effect, and they would restrict your ability to control exposure.

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  • STF lenses have a transmission rating (T-stop) much lower than their aperture rating (F-stop) because a portion of the objective area periphery is partially masked... – Steven Kersting Jan 2 '19 at 17:22
  • Opaque aperture blades block all light from passing through them. Apodization filters block some light passing through the periphery. This allows them to, for instance, convert the the bright edge of a bokeh ball into a gradual fade. Perhaps making the aperture translucent could similarly reduce the hard, shaped edge of bokeh balls into a gradual fade, regardless of the aperture setting. Also, light transmission would be increased, compared with opaque blades. Though DOF might be reduced. – xiota Jan 2 '19 at 23:17
  • If the blades were completely translucent it would have the same effect as shooting at the maximum aperture (blades invisible to the objective lens). If they were partially translucent they would have the effect of a reversed apodization filter... and that would have the opposite effect of what you are wanting. – Steven Kersting Jan 6 '19 at 17:34
  • Translucent, not transparent. Why oppoaite effect? – xiota Jan 6 '19 at 18:25
  • Because the errors an apodization filter minimizes are greatest at the periphery... i.e. vignetting, astigmatism, etc. And it does that by reducing the contributing light from the periphery. I.e. stopping down a lens increases the quality of bokeh, but that is different from "amount of blur." I found an article on simulating the effect that might make it more clear: petapixel.com/2018/02/12/… – Steven Kersting Jan 6 '19 at 18:38
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It looks like there exist lenses that do pretty much what you are describing - the Sony 135m/2.8 [T4.5] STF (originally a Minolta design) and the Sony 100/2.8 STF GM OSS. I don't own either lens, but from the descriptions I've read both lenses produce pleasing bokeh. I didn't see anything about an increase in depth of field, but the reports did talk about a loss of light transmission (the 135 uses T Stops instead of F stops because of this). Note that the lenses have "circular graduated neutral density filter" so it isn't just one density across the disk. I'm not an optics person, so I have no idea why that was done or what the consequences are.

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  • STF lenses have apodization filters in them. I am asking about a different method (translucent aperture blades) to attempt to achieve an effect similar to that of apodization filters. – xiota Jan 2 '19 at 16:59

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