Originally posted by carpents
My invention is this: take this idea of putting strangely-shaped cover over the lens and replace it with a graduated neutral density filter. The filter must have the gradations in a concentric circular pattern - darker towards the edges than in the middle. This will result in a softening of those out-of-focus highlights, creating a nice Gaussian blur instead of the typical hard edges. This might also help correct axial chromatic aberrations, which we've established here are pretty common.
What do you think?
I think you have "invented" the opposite of the filters used for fix vignetting (as with the Hasselblad Pan-X).
I'm not educated, nor an autodidact, when it comes to design anything optical. I'm happy by just using them... But my thoughts are that by placing something gradually in front of the lens it has a gradually visible effect. Think about these grad ND filters for landscape shooters.
I don't fully understand the details about why the Minolta 135mm STF lens works the way it does. I guess it has a lot to do with where the extra aperture is placed. Then again, sometimes one can get surprised so one should never say never... I have seen reports saying that placing a baffle (or an extra aperture opening between the lens and camera) can lessen flare from very fast primes. It sounds strange to me and the reports are a bit contradictory, as so often.
The extra set of aperture blades in the STF lens also closes the lens down, but with another effect than the ordinary aperture blades. The more a closed down, the lesser of bad effects from CA should be visible in the picture as the rays hitting the front element at it's outer areas are stopped. But that is basic, somewhere inside the lens all those rays of light are bent and diverted and I don't know what.
But the DIY stuff is interesting and if something can be done in this area I'm certainly interested.
Originally posted by d.bradley Sean,
Your idea does work, I'm currently digging up a thread on dyxum where some users had posted results from such a setup. The good news is that bokeh is largely improved, the bad news is that it someone else got to the idea first. My understanding is that the users created the graduated ND filters by printing on acetate. They also mounted the 'filter' inside the lens (closer to the back element). Something to do with vignetting? When the mods at dyxum find the thread, I'll post it here.
D
Very interesting. I look forward to learn more about this!
Thank you,