Quote Originally Posted by Emmanuel BIGLER View Post

However the when the shapes of this perforated disk are projected in out-of focus highlights, the visible shape is definitely non-natural and somewhat disturbing, I agree.

So with the Imagon, you should only take pictures of flat subjects with no depth, focused with the outer holes closed and then re-opened, if you want to see the added fuzziness but do not want to see the disturbing shapes in the background
Sorry, Emmanuel, but again I don't agree with the out-of focus-theme.
The main thing for creating disturbing shapes is direct light - of course in the out-of-focus-areas.
But it's not the out-of-focus area herself.
Again I read the manual of the Imagon, written by Michael Neumüller in his great book "the praxis of softfocus" from around 1950.
He describes " a special case is direct light, which requires closing the disk to avoid spreading highlights" (bedbucks).

He also describes the effect of increasing and decreasing the sharpness AND the glow by playing with the bellows distance but doesn't give a warning concerning spreading shapes in this situation.

I have learned to work with my Imagon exclusively from this book, so unfortunately I haven't more to say by own observations than this :-)

Concerning the iris of a shutter, let me throw in that Neumüller describes why it is best to put the iris in front of a meniscus (the Imagon is a kind of meniscus).

If the iris is behind the lens, this may give an effect which I can't translate exactly by word, but this may give problems at the edge between shadow and light.

I didn't use a meniscus with a shutter iris, but the resulting effect is described as a similary effect like burning a print in a bad way.

This effect seems to be more little, so I have problems to follow his examples given by pictures, but I want to spread the old news :-)

I didn't found the formula for the distance lens/front iris at this moment, but I remember nearly 10 percent of the focal length was given as the best distance.
I try to refind this formula.