Vitax de-focussing knob

[Stephane]

I dont understand what am I supposed to do with this knob. I focus on something, then turn the defocus know. But I can re-focus the image by moving the standards. I have not shot, just looking at the effect on the gg.
So my question is: one must focus on a subject, then defocus and leave it like that, or once the defocus knob has been turned, one is supposed to re-focus on the subject?
Any enlightenment would be greatly appreciated
By the way, the vitax is mounted on a sinar board, without cutting the flange (no magic trick here). I use it with a sinar p 8x10 and it is strong enough.

[Paul Fitzgerald]

Stephane,

either way works, you just choose which way works for you. I usually just leave it at 0 and adjust by focus and f/stop.

[goamules]

I have found the same fact; if you use the "soft focus" on a Vitax or Dallmeyer petzval, you can still refocus and remove all that softness. To me, it appears to do little, yet I still read in period publications about the soft focus features on these lenses. I still haven't looked carefully at negatives with a loupe, perhaps the effect is minor and I'm missing it with wet plate. The rear element was invented by Petzval to make more corrections for the front element, so you would think altering the lenses that "correct" would do more...

[Mark Sawyer]

I've had similar experiences with my 13.5" Vitax, but noticed that the edges remain softer with the soft focus dialed to full and the center refocused. My speculation is that moving the inner element increases the field curvature, as it's more out-of-focus than an aberrational soft-focus. I do find it a lovely Petzval to use, regardless.

[Stephane]

Glad not to be the only one. I will first opt for refocusing after setting the diffusion knob. Not refocusing makes the image out of focus, which for me does not mean "soft". Maybe on the 1 is enough without refocusing... Will see... Thank you guys.

[Louis Pacilla]

Hi Folk's

This is what I have noticed both on the G.G. & negatives when using this feature either w/ Dallmeyer's, Eastman Portrait, Vitax's.

If you look (you have to look) both on G.G. & negatives. The center of the negative(The REALLY sharp part) will be well just a little less cutting sharp.

I think the portrait artist was pleased to have this center area of the Petzval lens less sharp. To any degree. This Petzval lens as you well know is among the sharpest in the central portion of the projected image. so any softening of this area was a big plus.Who wants the crows feet, forehead wrinkles, pimples, warts and all the rest to be Petzval shard.

I Don't believe that fuzzy type lenses had been invented at this point.. so the designers idea of SOFT FOCUS was quit a bit different than ours.

Peace
Louis

[eddie]

it takes bit of study to see the subtle differences.

it is most easily seen on the highlights......have fun.

eddie

[jnantz]

stephane

you can also use the defocus knob to remove the bite
if you have the lens stopped down ( too much light for 3.8 ) .
the rear group moves around in the barrel, and gives a much better
effect than just focusing infront of the subject ...

have fun, i love my vitax too ...