Autofocus STF

[KevinBarrett]

Here's a fun avenue to explore: Why couldn't Sony put an apodization element (like the one in the manual focus only 135mm STF) in an autofocus prime lens? Naturally it would have to be a lens that had the appropriate architecture to use it, but there is a potential for a really sweet, exclusive, and affordable portrait lens. There's a huge gap in Alpha's prime lens range between 50 and 85... why not fill it with a simplified "A-STF" lens without the complicated aperture tricks?

[Dusty]

Quit using technical terms that I have to Google, Show Off!

Seriously, is this a soft-focus lens you're talking about? Center-sharp with blurring edges? (Google wasn't that helpful). If so, why not just do it now in software?

Dusty

[KevinBarrett]

The apodization filter is actually one of the lens elements, which is a neutral density tented glass that is thinnest in the middle and thickest at the outside. Its effect is not to vignette the picture, but to cause any highly contrasting details in out of focus areas to have a smoother transition, eleminating busy or distracting bokeh.

[Yagil Henkin]

I remember reading something about the STF being impossible to have screw-mount focusing for some reason. But maybe an SSM STF lens, with In-lens motor and no screw, is possible?

[Dusty]

The apodization filter is actually one of the lens elements, which is a neutral density tented glass that is thinnest in the middle and thickest at the outside. Its effect is not to vignette the picture, but to cause any highly contrasting details in out of focus areas to have a smoother transition, eleminating busy or distracting bokeh.

Couldn't the same effect be accomplished with a filter?

Dusty

[KevinBarrett]

Couldn't the same effect be accomplished with a filter?

Dusty

If a filter was made in the same way as an apodization element it would introduce some serious distortion. However, if a filter was made in the same way as an ipodization element, it would be made of shiny white plastic and play your MP3s.

[Dusty]

Okay then, it can't be done with a filter. This is why I don't get too much into arguments about lens designs. I can see the results of good glass, and appreciate it, but don't ask me to design the lens!

Dusty

[David Kilpatrick]

A similar effect could be achieved with a filter mounted in the aperture plane of the lens design. The problem would be getting the filter into the right place in the lens to eliminate darkening to the edges of the frame, you could not just use a centre filter (radially graded) on the lens front, the effect would be very different. Minolta just chose to overcome the problem of fitting a graded filter (using dye or coatings, which would both destroy sharpness) by making grey glass and then using this for a negative power element located near the iris.

David

[KevinBarrett]

I never understood, David, just what the necessity was in using two apertures in the 135mm STF lens. The most immediate benefit I could understand was that each iris has a different number of aperture blades (9 and 10), theoretically yielding a perfectly, more obsessively circular bokeh.