Velostigmat soft focus

[swmcl]

I have one of the aforementioned lenses.

When I go to twiddle the soft focus dial, I notice I can use the refocus control to bring the sbject back into focus.

When I dial in 0 soft focus and use the defocus control I seem to get a similar effect to using the previous method.

Can someone tell me that the soft focus control does something other than defocus the lens ?? Can't I do that with any old lens ?

Has someone inserted some lens elements out of a different lens ??

Cheers,

[Paul Fitzgerald]

"Can someone tell me that the soft focus control does something other than defocus the lens ??"

No because that is exactly what is happening. It works the same as 'scale focusing' with an old roll film folder, moving the front element to change focus distance.

"Can't I do that with any old lens ?"

Yes, you can. The advantage to the Wollensak is you can dis-assemble the front cell for cleaning & service and leave out the stop pin. You can now dial the softness to '15' (3 complete turns) and get true soft-focus without a chromatic focus shift. Works well if you like the effect and can be reset to (0) for normal use.

Have fun with it.

[goamules]

Paul, I'm not sure I agree that the soft focus setting on Velostigmats (or Cookes) is just defocusing. I believe they actually increase the spherical aberration, causing an overall softness that cannot be undone by refocusing. For example, if we go to maximum level diffusion (or more, as some people alter these lenses to unscrew beyond the 5 mark), you will have a soft image. You cannot adjust the focus at that point to get it sharp again.

[Brian C. Miller]

Since spherical aberration comes from the shape of a lens, how can it be induced with the turn of a lever? An element would need to be swapped out to change the spherical aberration.

[goamules]

Since spherical aberration comes from the shape of a lens, how can it be induced with the turn of a lever? An element would need to be swapped out to change the spherical aberration.

Because for every lens design the different refractive indices of different types of glass, and their shape, and their spacing, controls spherical aberration. Changing that spacing "messes up" the optimal, sharpest setting.

What do you think happens when the spacing is changed using the adjustments on a Velostigmat or Cooke?

[Paul Fitzgerald]

"Paul, I'm not sure I agree that the soft focus setting on Velostigmats (or Cookes) is just defocusing. I believe they actually increase the spherical aberration, causing an overall softness that cannot be undone by refocusing."

In it's factory arrangment it only re-focuses the image. Have not noticed spherical aberration (curved field, non-rectilinear) If you leave out the stop pin and crank the 'fuzz-U-lator' to 15 it becomes a true soft focus.

The Universal Heliar, Portrait Unar and Cookes move an internal element changing the focal length, inducing spherical aberration and inducing a slight visual - to - film focus shift. Verito, Varium, Kodak Portrait and modified Unar have the same shift wide open, stopping down helps all of them BUT may ruin the image you're after so these all take some time to play with and learn.

[Mark Sawyer]

Here's a thread with probably more information than you want:

http://www.largeformatphotography.in...ad.php?t=57385

[Nathan Smith]

As I recall, Jim Galli did some tests like this using a standard Velostigmat & adding extra space between the elements. Darned if I can find that thread now though.

[goamules]

...In it's factory arrangment it only re-focuses the image. Have not noticed spherical aberration (curved field, non-rectilinear) If you leave out the stop pin and crank the 'fuzz-U-lator' to 15 it becomes a true soft focus...

So you are saying changing the lens separation a little does not induce more spherical aberrations, but doing it more does? I don't think so. Just because one cannot easily see the effect, doesn't mean it's not there. All the writing about the Velostigmat that I've read going back to the 1910s explains the 0-5 adjustment as diffusing and softening the image via Spherical Aberration. (Now the Vitax is a different matter, on that one I can get the original sharpness back by refocusing).

...There are three anastigmats which lend themselves very well to the production of pictorial work with softer definition. The Dallmeyer is so calculated that by unscrewing one of the lenses a uniform softening of the image takes place through the introduction of a small amount of spherical aberration. The Cooke also has this property when the front glass is loosened normal lenses notwithstanding will give microscopic sharpness when this is desired. The Wollensak 4.5 [Velostigmat] has a diffusing device in the larger sizes...Certain special generally known as soft focus or semi achromatic lenses are particularly designed to possess an amount of spherical aberration."
The Elements of Photography, (1919, Fraprie)

I propose it's a linear diffusion. I imagine what you are seeing as focus shift occurs anytime you change the configuration of a lens, so yes, there is a focus change too.

[Marko Trebusak]

While adding diffusion on these things the focal length changes as well. So if you focus sharp and add diffusion, you'll get out of focus image and not soft focus. Same is true for Cookes. So if you focus soft and don't see much happening, that's because there isn't much in the objective to happen.

But I urge you to read the thread Mark pointed to. As he said there is more in it that you would like to know ;-).

Cheers,
Marko