Diffusion and out of focus

[tkamiya]

I'm putting this question in MF forum because that's the format I intend to use for this... but it really applies to ANY format.

What's the difference in results between:
1) soft focus lens
2) regular lens with out of focus image
3) regular lens sharply focused with soft focus filter attached
4) soft focus lens that comes with diffusion disks (like RB lens)
5) printing sharp neg with various diffusion technique at the print time

concerning 5, I do know, at the print time, use of diffusion makes shadow defuse into highlight. My understanding is, use of diffusion filter at the shooting time results in highlight diffusing into shadow.

 

[jp498]

1/2. Many soft focus lenses are both in focus and out of focus at the same time. They have a mix of sharp in-focus and other aspects that render with out of focus or glow or whatever. This is caused by various optical means, the basics being spherical and chromatic aberration to blend the focus. Stopping down usually corrects these, so soft focus is usually done at the wider apertures. Essentially the lenses are imperfect by design.

3. The soft focus filter doesn't provide the same sort of bokeh provided by a traditional SF lens and may handle the glow differently compared to what you're comparing it too.

4. I think the diffusion disks allow the SF lens to be used a smaller apertures than traditionally wide open or close to wide open.

For the long answer, google "russell young thesis pictorialism"

 

[ic-racer]

Some of the questions are answered here: http://www.trenholm.org/hmmerk/TIAOOFe.pdf

 

[David A. Goldfarb]

Just to add to the above, the idea of the "sink strainer" discs on lenses like the Imagon and star-shaped apertures on some of the traditional soft focus lenses is not to cause diffusion, but to preserve the spherical aberration of the lens while reducing the exposure. It could be interesting to compare that effect to the effect of an ND filter, so you would get the spherical aberration without the sink-strainer shaped highlights.

Stopping down with a traditional round iris reduces spherical aberration, so lenses like the Verito have most of their glow in the range between wide open and f:8, though you'll still get chromatic aberration at smaller apertures.

Another thing is that each of these lenses has its own unique look. You can try to make one thing look like something else, and you might get something interesting, but it won't be quite the same.

 

[jp498]

If you want to get all crazy with soft focus stuff, LF is where it's at. Of course you can use a MF back with LF, but most prefer the sheet film.

 

[tkamiya]

I don't want to get ahead of myself.

I started wondering about soft focus because I had a model who showed up with skin imperfections. It could have been covered up with some make-up but she didn't and I didn't notice it while shooting. I was wondering about various options available.

 

[removed account4]

TK

in the printing stage you can pass a sheet of the plastic paper that
wraps tea boxes to diffuse the image a little ... 1 pass under the lens goes a long way !
you can also look for an old folder or junk box camera and use one of those lenses
instead of a sharp enlarging lens ... or put nylons on the enlarging lens with a hole burned through it ...
all the things you can do at the taking stage to soften an image can also be done in the enlarging stage -

have fun !
john

 

[tkamiya]

John,

Yeah, I know. I acquired some of that materials and I was going to try it. I'm going to have to learn a lot of new techniques and quickly! I have some junk enlarging lens that I might try - that's a great idea.

By the way, I'm trying not to add any more equipment. I have enough. Time to learn how to get the most out of what I already have!!

 

[jeffreyg]

Pertaining to #3. B+W has two types of soft focus filters each with 2 grades of softness. One is called "special effect attachments Soft Focus I & II. It has concentric rings in the glass surface. The intensity of of the effect is influenced by the aperture with the larger the aperture the softer. It also reduces contrast and increases flare. The second is the classical Softars I and II which have tiny lenses incorporated in the filter's glass surface and is not affected by aperture.

There is also a Soft Image filter that is softer than the Soft Focus II that is also independent of the lens opening. Other brands probably have similar filters.

http://www.jeffreyglasser.com/

 

[Sirius Glass]

Dodge the blemishes with a nylon stocking. Several layers if necessary. That is assuming that you can find a nylon stocking.

 

[David A. Goldfarb]

The soft filter with the etched concentric rings is generally known as a Duto filter.

 

[olwick]

I know this isn't appropriate for this forum, but if you go to the hybrid forum and search for Portrait Professional you'll find what you need.

 

[tkamiya]

Thanks for the tip. I know the product but that's not what I want to do.

 

[polyglot]

I'm putting this question in MF forum because that's the format I intend to use for this... but it really applies to ANY format.

What's the difference in results between:
1) soft focus lens

These are usually lenses with high (and sometimes adjustable) spherical aberration (SA), which means two things:
- your bokeh will look better either in front of or behind the plane of focus because its edges will be rounded
- the focused image will be a blend of focused and unfocused light, so it glows a bit

2) regular lens with out of focus image

Assuming no SA, the image is a convolution of the scene with a disk, the diameter of the latter being a function of the aperture size and how far out of focus each item is. So a point light becomes a disk, a 0-width line becomes a fat line, a non-zero-width line becomes a fatter line with penumbra. Note that because the disc has sharp edges, your defocused areas in the image will still have sharp edges. Focused areas in the image are effectively convolved with a 0-diameter disc, i.e. they remain focused.

To go back to (1), the presence of SA means that your bokeh discs no longer have hard edges, so the bokeh can look a little more pleasing. However, overcorrected SA means you have nisen bokeh (hard rings of light with dark centres), which are ugly and can result in nasty effects like line-doubling. With the adjustable-SA lenses (e.g. the Nikon Defocus Control lens), you can set it for good performance for the background or the foreground but often not both - you'll get good bokeh one side and nisen bokeh on the other.

3) regular lens sharply focused with soft focus filter attached

I think this is a diffusion effect, which gives you a blend of focused and unfocused light. I haven't tried it though and there are many ways of constructing such a filter (circular etching, microlenses, nylon stockings, vaseline on a clear filter) and they all give subtly different mixings of light.

4) soft focus lens that comes with diffusion disks (like RB lens)

These (the sink strainers) are not diffusion disks but (as far as I know) something between an ND and an apodisation filter made out of metal, though it's possible that maybe the outer, tiniest holes will have diffraction. Their purpose is to reduce exposure while still giving you access to the full diameter of the aperture, which will maximise the diameter of the blurred areas of the image and the presence of any SA. They have no effect on in-focus parts of the image (except for maybe some diffraction but I'm not sure), and the out-of-focus parts will become a convolution of the scene with the holes in the sink strainer, so instead of getting a single disk from a point-light, you will get a bunch of smaller discs.

The natural evolution of this approach is to use a continuous-tone apodisation filter in the lens so that your bokeh has a gaussian form instead of a disc; that's what the Minolta/Sony 135mm STF does. It introduces no additional diffraction, has practically no SA and therefore no reduction in sharpness for the focused area (and no glow), but it gives you perfect bokeh front and back with no sharp edges at all.

5) printing sharp neg with various diffusion technique at the print time

This is a mixing of light, but negatively. Unless you're printing from a slide onto Ilfochrome or some other reversal-paper

concerning 5, I do know, at the print time, use of diffusion makes shadow defuse into highlight. My understanding is, use of diffusion filter at the shooting time results in highlight diffusing into shadow.

Yes. As you observe, you get anti-glows from this technique.

 

[tkamiya]

Thank you.