Hi Carsten,

No want or need to list the Top Ten and start a bidding war but I will try to explain the types to look for.

First, the simple magnifying glass, completely uncorrected and a pain to place an aperture in front of BUT can have an interesting look to it.

Next, the simple meniscus, very popular as a portrait lens, these can run from very soft to more than sharp enough, usually expensive. Spencer Port-Land, Grundlach Portrait Meniscus, Pinkham Smith, Straus, Imagon, Fuji SF, Kodak Portrait Lens 4.5.

Next, Petzval, not really soft-focus but do have a curved field and lovely fall-off, a very nice look, from historically collectible expensive to fairly cheap.

Next, oversized RR/Aplant, purpose built to f/4 for portrait work. These are the most highly prized and expensive SF lens and are too large for a field camera. Pinkham-Smith, Hyperion, Eidoscope, Nichola Perscheid, Portrait Euryscope.

Next, oversized modified RR/Aplant, purpose built to f/4 for portrait work. These are highly prized and fairly expensive SF lens and are too large for a field camera. Verito, Veritar, Photoplastic Portrait, Plastigmat Portrait.

Next, the Cooke Triplets, these were very popular and made by most companies, from f/3.5 - f/5.6, with or without adjustable soft-focus, and from very highly prized to unknown, unloved and unwanted. TTH Cooke, Varium, Cassar, Hypar, Sigmar.

Next, the modified Cooke Triplets, Heliar and Tessar. These are not soft-focus lenses, actually professionally sharp but the OOF rendering is soft and smooth. They usually come with mega-blade apertures for a perfectly round iris which makes the transition from the focus plane to the OOF very distinct leading to a very 3 dimensional rendering. Most of the 360mm and longer appear to be optimized as studio portrait lenses. This could be why they are THE most popular portrait lenses used across the planet. Heliar, Tessar, Ektar, Xenar, Ysar, Raptar.

Last, the dialytes, Unar and Dogmar. These are normal lenses but B&L did make an adjustable soft-focus Portrait Unar and the Goerz Dogmar is triple convertible and very soft when converted. The process lenses may have a nice look but they are not soft-focus and usually too dark for portraits.

All of the above will lose their soft-focus look by f/11 and should be completely sharp by f/22.

Hope it's a help.