Velostigmat w/Diffusion ring: How to tell if it works ?

[Ken Lee]

I just got a 12 inch Velostigmat Series II with the diffusion ring.

With the lens wide open, I focus on a subject. The in-focus area is sharp, and bokeh is quite smooth.

When I change the diffusion ring, I can either refocus or not, because the image is now a bit blurry.

If I don't refocus, then the image is soft. If I refocus, then the image looks the same as the original image.

Is that what the diffusion ring is supposed to accomplish ? If so, why not just leave the lens out of focus in the first place ?

... Or should I return the lens as defective ?

[Ash]

That kinda sounds like "my soft focus lens makes things look blurry". I can't help but by the sounds of it the diffusion ring effectively softens edges, and that makes an image blurry.

[Ken Lee]

Jim Galli has contacted me off-line, and alleviated my worries.

As you are suggesting, that's how the lens is supposed to work: don't refocus.

[C. D. Keth]

The ring on the velostigmat just changes the focal length very, very slightly. The idea is to throw the whole thing a tid bit out of focus.

[jnantz]

ken,

if the ring is like the ring on a vitax
it moves the back group, so if you have to stop down,
you can still de-focus and get a soft image.
my vitax is in a studio shutter, and the defocus knob comes
in handy if i am not in dim light ...

have fun !

john

[Jon Shiu]

Hi, just to note, the ring moves the front element outward from the zero position.

Jon

[jnantz]

thanks jon
didn't mean to dis-inform

john

[Ken Lee]

I found this info posted by Clive Warren at http://www.f32.net/discus/messages/6/99.html?1054486436:

"This diffusion adjustment is operated by revolving the front mount(numbered 0-5) AND THEN STOPPING DOWN to obtain the necessary degree of depth. Do not refocus after having set the diffusion adjustment at any number, as this will have a tendency to do away with the desired softness. It will be found that when the lens is used in this way, it will not throw the subject out of focus, or change the general effect in any way, except to eliminate the sharp definition and give that softness or roundness so much desired in portraiture."

[Ken Lee]

The diffusion ring is quite stiff. Is there a simple repair procedure ?

If not, to whom should I send the lens for CLA ?

[Jon Shiu]

Hi, the whole ring/front element screws completely off. Maybe take it off and clean and lube the threads. Mine will just unscrew completely off the lens by just turning the ring.

Jon