Many/most SF lenses vary diffusion by aperture, and with these, wideopen is where they're softest.  You can further change the degree of softness of these lenses by using differing combos of lighting/tonality/distance from the SM.   These lenses don't do the work for you, they force you to work hard and when you get results you like, it's in spite of the limitations of this type of glass.

Some SF come w/a diffusion ring like the Velostigmat, where you can dial in diffusion.   Very few lenses w/their ability to 'dial in' fuzz, compare to the amount of diffusion you can 'dial in' w/the Velostigmat after removing it's limiting screw which was used to limit the front element from being screwed out less than one revolution.  

After the removal of this screw, you can rotate the diffusion ring and thus the front element approx. 3/8" from the barrel which is about 1-2 revolutions before the diff ring/front element will come off.

After some testing, my use of the Velostigmat evolved into establishing a 'sweet spot' which was an intermediate position between the diff ring being flush up against the lens barrel and it's most extreme position of screwed out 3/8 away from the barrel.  I taped off this 'sweet spot', and was content for awhile to leave the lens in this configuration.

It then occured to me that I wasn't using the lens to it's full potential, or at least trying to.   The original idea of the Velo w/diff control was a good idea, the creators of the lens just didn't go far enough, and they limited the original diffusion control screwing in/out less than one revolution.  I then resolved to do the same thing the creators of the Velo did, but w/default positions spanning flush up against the lens barrel, to screwing the front element 3/8" out and away from the barrel.

Just screwing a filter on a lens takes quite a few revolutions, and unscrewing a threaded lens element out 3/8", is a lot of screwing/unscrewing, a lot of revolutions.   I asked myself how I was going to know and be able to return to the exact position of my 'sweet spot' after taking the tape off and screwing the front element in or out to another position?   How was I going have several default positions, and the ability to go back to those positions, if I found that at those positions a particularly 'nice look'.

I have a micrometer somewhere, it's hiding somewhere and won't come out, and it was hard for to use the thing anyway, so I considered that, and then said 'no'.  

I considered counting revolutions/marking down the number of revolutions to any particular spot, and then I tried it, and of course decided I didn't want to go through life w/one of my arms and wrists twice as long and twice as thick as the other one.

I couldn't think of anything, and then I just spent some time looking at the lens w/the front lens element/diff ring screwed out about halfway, and how this formed a groove/gap. 

I thought about the thickness of the gap, and I thought about 'post its', which are the approx. 3 inch square and very thick yellow pads of paper w/adhesive holding all the sheets together at one end which secretaries and legal assts. tear off sheet by sheet and use as notations stuck to documents.

Besides a 'post it' being a number of sheets of paper stuck together to form a pad, I thought of each sheet of paper as a shim, of equal thickness, and how I could stick a thickness of one of these pads/a number of sheets from a pad, INTO THE GAP formed by screwing out the diffusion ring/front element to any one position, and KEEPING that thickness as an EXACT measure to return to the front element to that position.

I took the tape off securing the front ring/front element in its aforementioned 'sweet spot', and guestimated a thickness of one of these 'post it' pads, between my thumb and forefinger and stuck it into the gap created by screwing the front element away from the lens barrel, and kept adding individual sheets until the thickness of the sheets 'popped' snuggly into the gap.  

I then tore that thickness of papers off the pad, and knew that regardless of how I changed the position of the ring by screwing in or out, I could always return to that spot by screwing down to the exact thickness of the pad I just tore off.

I have 4 default positions I've established w/my Velo w/diff control, 2 are the 2 extremes, screwed all the way in, flush up against the lens barrel, and screwed all the way out and about 2 revolutions from fall off.  I don't need the above mentioned technique of using 'post its' to establish those positions.

I have two intermediate positions or 'sweet spots' between the 2 extremes where I've used the 'post its' technique to establish the size of the gaps which correspond to those positions, and so this is repeatable every time, exactly.

The top most image is of a thickness of a 'post it' pad which has been torn off, stuck into the gap of my first intermediate position and the shot below this illustration is an example of the look from this position.

The bottom shot is the front element/diff ring screwed out 3/8" from the barrel. 

I'm sure some folks have developed other systems, but I thought I'd mention this technique because of its simplicity.

Addendum:  The 2 shots below the illustration are test shots put together quickly.   The 12" Velostigmat w/diff cont. was the very first soft focus lens I'd bought, having been inspired by seeing a photo by Chad Davis taken w/this lens many years ago, and I've always thought this lens was underused/unloved/unappreciated for what it can do.  

I've seen quite a few shots via the Velostigmat II w/and w/o the limiting screw in place, and many of those shots including mine have tended to be 'low key', but with the right lighting set-up, this lens can compete the 'sparkle' and 'excitement' of the Semi-Achromats, the Kodak Portrait lens, and other legends out there given the right lighting.

I've had this lens for years, w/several shots on my personal website done w/this lens, so I'm tickled by the new interest in this glass.   The 'cat is out of the bag' about the limiting screw, which is what prompted me to write this journal.

  I'll give one of my shots an encore which was shot with the limiting screw taken off I did a coupla yrs. ago, which i think shows what one this lens can so with some intense backlighting.   

Incidently, speaking of backlighting, and the 'glow' that these lenses tend to produce, nothing's worse to me than shooting a shot and including the 'glow' because you couldn't do anything about it/couldn't get rid of it, ........................it ought to be there because it helps the shot, and if it doesn't, it's got no place being in the shot.   This is what I told myself throughout my learning curve w/this lenses, which is to learn how to use 'em w/the glow, and learn how to get rid of the glow when it doesn't work for the shot.

This encore shot which has plenty of glow/flare which I think works for the shot is I think, representative of when what these lenses do.  

Incidently, I've not photoshopped this pic, I can duplicate any of the shots I've uploaded here, anytime, they'll look the same through the viewfinder as how I shot 'em, if you think otherwise, then by all means, stay away.  This shot is how I saw this SM through the viewfinder, and I love the energy and the 'glow' which of course is has been OVERUSED ad nauseum, ad infinitum, but not in this case.

This is '3 Shot Glasses, which I've uploaded before, it's from my third intermediate position in relation to the diff ring/front element being screwed out and away from the lens barrel.