I've had the opportunity to try out the Sony 100mm f/2.8 STF GM lens over the last few days, amd can't help but get the feeling that they took a useful, if situational, technology and put it in the wrong lens.
Yes, it's a ridiculously sharp lens, with very smooth bokeh wide-open. But what is it for? Specifically, why put the STF element in a lens like this?
As a portrait lens, 100mm f/2.8 doesn't really blur the background enough. The fact that the bokeh is smooth doesn't change that. Even for head shots, or head-and-shoulders shots, where you'd often be shooting at f/4 or so for depth of field, you'd often want a longer lens for telephoto compression and increased background blur. If you're shooting in a studio or don't have a busy background to deal with, the STF is superfluous anyway.
It would seem that the STF element would have been much more useful in a 105/1.4, 135/1.8 or 200/2 lens, where the smoothness of the bokeh could be combined with adequate overall background blurring. Or in a supertelephoto lens (say, 500/4) for shooting wildlife against busy backdrops (especially leaves or grass).
Furthermore, STF is a very situational feature. It's fantastic when you have a shot that can benefit from it (masking and applying Gaussian blur in Photoshop to achieve the same effect can be difficult and time-consuming) but, when you don't need it, it just sucks up two stops of light. Would it not be more flexible either as an element that can be swung in or out of the light path (like an inbuilt teleconverter) or, even better, as a radial GND filter, with a clear centre and dark edges, to be attached to the front of the lens or used as a drop-in filter in larger lenses?
Anyone else used it and have other thoughts on it?