It’s difficult to get a soft-focus image that looks good – that’s why lens designers have created special lenses like the Pentax 85mm f/2.8 Soft. Lenses like this are designed deliberately to exhibit large amounts of Spherical Aberration, producing the soft look common to lenses from the early days of photography. Spherical Aberration means that the lens focuses light from its periphery at a different distance than light from near its center.
Filter makers have made various filters that attempt to emulate this look and photographers have tried many home-brew filtration techniques with the same idea: smearing Vaseline on a clear filter or stretching nylon stocking material over the lens (the latter technique was used to shoot many of Ingrid Bergman’s close-ups in Casablanca). None of them can truly duplicate the look of spherical aberration, though that doesn’t mean they aren’t useful.
Lately Photoshop has come to the aid of photographers wanting to get the soft-focus look. Like the mechanical filters, it can’t really duplicate the look of spherical aberration from a true soft-focus lens, but with a little work it can come closer than the filter/Vaseline/stocking approaches and has the added advantages of being controllable and undoable. With a filter (or a special lens) once you take a soft-focus shot you’re stuck with a soft focus shot. With Photoshop you can get a sharp photo and several different intensities of soft-focus photo from the same shot.
Open the image you want to edit in Photoshop. If it’s a multi-layer image you’ll need to flatten it and save the flattened copy under a different name.
Start by making two copies of the background layer. The fastest way of doing this is with the Control-J (Win) or Command-J (Mac) keyboard shortcut. Use it twice and you should see something like this in your Layers panel:
Hide the top layer (by clicking the eye icon to the left of "Layer 1 copy" in the Layers panel) and select the middle layer, "Layer 1".
We want to brighten this layer a lot, but to make this brightening adjustable later, we’re going to do it with an Adjustment Layer.
Make sure you’ve selected the middle layer (Layer 1 in our example). Then click the Adjustment Layer Icon (the half-black/half-white circle in the middle of the row of icons at the bottom of the Layers panel). Select "Curves" from the pop-up list that appears. This will add a Curves Adjustment Layer just above Layer 1.
By default, Adjustment Layers apply to everything beneath them in the Layers panel, but we want this adjustment to affect only the middle layer. To achieve this, place your mouse pointer on the dividing line between Layer 1 and the Adjustment Layer above it in the Layers panel. Press the Command and Option keys (Mac) or Control and Alt keys (Win) and the cursor should change to a pair of interlocking circles (as shown at right). Click with the mouse and the Adjustment Layer will be linked to Layer 1 alone and won’t affect the background layer. (Put your mouse pointer over the image at right to see the before/after of this step.)
If the Adjustments Panel isn’t showing, go to the Window menu and select Adjustments. Click once on the Adjustment Layer ("Curves 1") in the Layers panel and you can then adjust the Curves in the Adjustments panel. Drag the handle at the lower left end of the curve upward a little and add a handle somewhere in the middle of the curve and drag it upward. A typical curve is shown at right, but the optimum setting varies widely from image to image. Experiment: This is an Adjustment Layer, so you can change it as much as you like at any time without damaging your original file.
Now we need to add some blur to this middle layer. In order to make it adjustable later, we’re going to use a "Smart Filter", so we first have to convert Layer 1 into a "Smart Object". Make sure Layer 1 is selected (not the Adjustment layer) and, from the top menu, click Filter > Convert for Smart Filter (if a confirmation dialog pops up just click "OK").
Now click Filter > Blur > Gaussian Blur from the top menu. The optimum amount of blur varies with image size: For a web image an 8-15 pixel radius could be right; with a 6-megapixel image, try a radius setting around 20-30 pixels; with a 25-megapixel image, a 50-60-pixel radius is likely to be closer. Image characteristics play a big role – Portraits can take more blur; shots with a lot of fine detail can withstand less. The range that works for images of various types and sizes is huge (5 pixels to 75 pixels) — Experimentation is the key.
Next we want to change the Blend Mode of our lightened/blurred layer. Select "Overlay" from the Blend Modes options in the Layers panel as shown at right. You may want to lessen the effect by reducing the opacity of this layer. (If you’re familiar with the blend-if sliders in the Layer Style panel you may want to try making the darkest and/or brightest pixels semi-transparent, but that’s a topic in itself that I don’t have space or time for here.) An opacity setting between 50% and 100% usually works best for this layer.
Now lets go to the top layer, which we’ve kept hidden until now. Select this layer and turn on the layer visibility (the eye icon in the Layers panel). If you want you can also convert this layer for Smart Filters, but this layer is less critical, so a standard filter will probably suffice. Add some Gaussian Blur (Filters > Blur > Gaussian Blur), but much less than you applied to the middle layer: a web-size image may need a radius of just 1 or 2 pixels and a really big image rarely needs more than 10-15, depending on image size and the amount of detail present. No tricky Blend Modes to play with here, just dial down the opacity until you get the effect you want. An opacity setting between 10% and 50% usually works best for this layer.
You can experiment with the opacity of the two image layers to get a variety of "looks". You can also tweak the Curves Adjustment Layer and the Gaussian Blur filter of the middle layer to vary the effect. Color balance and saturation can be affected by this technique, so if you’re really picky you can add a Hue/Saturation Adjustment Layer to the overall image to tweak it to perfection.
It takes a little practice to get the hang of this process but it’s not terribly difficult and gives you a wide range of soft-focus intensities in a controllable format. My preference is for fairly subtle effects (the example below is deliberately overdone for emphasis) that give the final image a little "glow" but some portraits can benefit from a fairly heavy approach. Give it a try.