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



Ken Lee
6-Apr-2007, 07:27
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
6-Apr-2007, 08:10
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
6-Apr-2007, 09:34
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
6-Apr-2007, 10:57
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
6-Apr-2007, 14:04
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
6-Apr-2007, 14:17
Hi, just to note, the ring moves the front element outward from the zero position.

Jon

jnantz
6-Apr-2007, 16:31
thanks jon
didn't mean to dis-inform :)

john

Ken Lee
6-Apr-2007, 17:45
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
8-Apr-2007, 06:07
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
8-Apr-2007, 08:10
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

Paul Fitzgerald
8-Apr-2007, 08:12
Ken,

Simply answer is warm it up, the grease is dried out.

Real answer is you have to dismantle the front lens cell completely. You may be able to reach the front set-screw by removing the rear glass of the cell and then unscrew the adjustment ring. On most you must remove the front beauty ring/ nameplate to access the set-screw. No idea who to send it to.

Have fun with it.

Mark Sawyer
19-Jun-2007, 11:08
Forgive my bringing up an old thread, but I'm a bit confused still as to how the diffusion should be used. In Clive Warren's thread, he states:

"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."

(He cites the original source as a 1914/1915 Wollensak catalog describing the Velostigmat Series II f4.5.)

However, in the same thread, there's a scan of an undated Wollensak catalog that indicates you do refocus after setting the diffusion ring. (The pertinent section cropped below). Anyone with the definitive answer?

Ken Lee
19-Jun-2007, 14:33
For what it's worth, I returned mine to the seller. I'm sure it has or will make someone else very happy.

I discovered that what I want is a silky smooth rendition (http://www.kenleegallery.com/html/gallery/mht180.htm) of areas that are purposely out-of-focus, rather than a soft-focus effect over the entire image.

But that's just me.

Toyon
19-Jun-2007, 15:19
Ken, before you go for some fancy lens, try a tessar or rectilinear lens. They have much nicer out of focus definition than many modern designs, but can be plenty sharp.

Jim Galli
19-Jun-2007, 15:33
Forgive my bringing up an old thread, but I'm a bit confused still as to how the diffusion should be used. In Clive Warren's thread, he states:

"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."

(He cites the original source as a 1914/1915 Wollensak catalog describing the Velostigmat Series II f4.5.)

However, in the same thread, there's a scan of an undated Wollensak catalog that indicates you do refocus after setting the diffusion ring. (The pertinent section cropped below). Anyone with the definitive answer?

Now I'm really confused. I've been happily doing it wrong but this seems to be the gospel straight from the apostles doctrine. Anybody got the tech help line for Wollensak so we can call and ask?

Ken Lee
19-Jun-2007, 15:44
Thanks -

I ended up acquiring some older Tessars and Heliars. They do very well in this regard, the Tessars being the best - for my taste - as illustrated in the photo to which I linked in the previous post. As you point out, they really are plenty sharp when they want to be, even wide open. Were it not for their comparatively limited coverage, I wonder whether other lens designs would have ever flourished after the invention of the Tessar.

The Heliar has something else, for which I haven't quite found words. I have not found its OOF as smooth as the Tessar, but it has... something else.

On the other hand, I have found that some of my modern lenses do quite well too - when shot wide-open. For example, the Fujinon 240A and 300A, when shot wide open at f/9, have superb OOF rendition. The same is true of the Fujinon 450C when shot wide-open. Because they have 5-bladed diaphragms, however, their OOF rendition suffers, as soon as they are stopped down even a little.

Most interesting to me, is that my 150 APO-Sironar S has rotten rendition of OOF when shot wide open. In fact, it is the worst among the lenses that I have tested.

Mark Sawyer
19-Jun-2007, 16:21
BTW, the Velostigmat *is* a Tessar, and I think a very nice one with pretty sharp resolution, very smooth transitions and lovely out-of-focus rendition. Forget the mysterious diffussion ring and it's still an under-rated keeper for me!

(But I'd still like to know how I'm supposed to use the damned thing...)