Extended Depth Of Field

How deep would you like your depth of field? The choice is yours. Today, there are virtually no limits. You can extend depth of field beyond the physical limitations of any lens/camera system with multishot exposure practices and software that composites multiple exposures.


1) Foreground in focus


2) Background in focus


3) Two exposures combined to achieve infinite depth of field

To do this, you first need to make a set of focus-bracketed exposures, optimizing focus in different image areas. How many exposures you’ll need will depend on how much depth of field a scene contains. At a minimum, make two exposures: one focused on the foreground and another focused on the background. Making three exposures is better, one each for foreground, middle ground and background. When dealing with extreme depth of field, like macro photography, you’ll want to make more exposures, at least three, probably six, possibly more. When in doubt, make more exposures than you think you’ll need; you don’t have to use them all when you stack the separate exposures, but they’ll be there if you need them. Unlike bracketing for HDR, it’s almost impossible to automate these types of bracketing sequences in-camera as focus needs to be adjusted for each frame. However, for tethered shooting, you can use software such as Helicon Remote to take control of your camera and automate this process and other bracketed sequences like HDR and time-lapse. Whenever possible, use a tripod to make focusing during exposure more precise and registration during postprocessing easier. While using a tripod always delivers more reliable results, don’t let this stop you from trying this technique handheld, especially with simpler sequences, like those used in landscape. You may notice that in cases involving extreme depth of field, the relative size of objects may change between individual exposures. These effects will be adjusted automatically during the merging process.


4) Photoshop’s auto-masked layer stack

Before you combine a set of focus-bracketed exposures, make all the RAW conversion adjustments you’d like to make to the final file. It’s quick and easy to process a focus-bracketed series of files; process one file in the series ideally and then sync the other files to it. Once a RAW file is rendered, you can’t reaccess the data in it, such as "recovering" highlights or "filling" shadows, without re-rendering it. While you can adjust lens distortions after stacking with Photoshop’s filter Lens Corrections, it’s much easier, faster and more robust to apply Lens Corrections during RAW conversion, before focus stacking 16-bit TIFFs. And while you can make adjustments to files in Photoshop that are similar to Adobe Camera Raw’s or Lightroom’s white balance, noise reduction and Clarity, they’re not identical.

Once you’ve processed a set of focus-bracketed exposures, you can automate the process of stacking and blending them into a single file in Photoshop. Take these steps:

1. Select the exposures to merge— File > Automate > Photomerge.
2. Choose the blending method or let Photoshop choose for you; Auto usually works well.
3. Click OK, and Photoshop will do the rest, making each file a layer in one document, aligning them and masking them to reveal the sharpest information.


5) Helicon Focus’ main window

If this method fails (sometimes it does, unpredictably), try this route:

1. Select the exposures to merge—File > Scripts > Load Files Into Stacks, checking Attempt to Automatically Align Source Images.
2. In the Layers palette, highlight the separate layers by Shift- or Command-clicking them.
3. Go to the Edit menu and select Auto-Blend Layers.
4. Photoshop automatically will mask the layers to reveal the sharpest image areas.

You then can further refine these results, including manually adjusting the automated masks or distorting layers, but this is rarely necessary. Photoshop does a fine job for a majority of applications.

When you’re looking for the highest quality, consider focus stacking with Helicon Soft’s software, Helicon Focus. It delivers superior sharpness consistently and can be used to batch-process multiple focus-bracketed sequences. Take these steps:

1. Click the Add Images icon; select the exposures to be combined.
2. Click the Render button to save a combined result.
3. Option: Choose a Method other than the default Method B (Depth Map)—Method A (Weighted Average) or Method C (Pyramid).
4. Option: Use the Radius slider; this helps refine the software’s search for focused sources by specifying a line width to favor.
5. Option: Use the Smoothing slider; lower settings generate sharper results, while higher settings create smoother transitions between sources.
6. Option: Use the Autoadjustment dialog to refine image alignment.


6) Helicon Focus’ Autoadjustment panel

Why not just selectively sharpen images to achieve similar effects? Digital sharpening skills aren’t a substitute for focusing skills, rather they’re an enhancement to them. Optical sharpness is superior in quality to digital enhancement—plus, it’s more flexible. You’ll be able to achieve superior digital sharpening results with better focused image sources. After all, no amount of digital sharpening wizardry will make truly out-of-focus images appear to be in focus—yet. In the not-too-distant future, focus stacking will be performed automatically in-camera during exposure, and depth of field will be controlled by sliders during postprocessing. Today, it still pays to know how to focus. You can go way beyond autofocus with focus stacking. You can surpass the limits of traditional tools and techniques with these new practices. Focus stacking works more like our eyes and mind work together in concert with one another than the camera eye does on its own. In fact, you can do what’s impossible to do with either eye or lens at one moment in time, like focus two parallel planes at significantly different distances.

You can get highly technical with this technique, but I recommend keeping it as simple and practical as possible—so that you’ll use it more frequently. Develop this new habit, and you’ll quickly find many situations where focus stacking will help you make images of superior technical quality, sometimes subtly superior and other times dramatically superior.

Visit this url to read more on depth of field: www.johnpaulcaponigro.com/downloads/technique/exposure.php.

John Paul Caponigro, author of Adobe Photoshop Master Class and the DVD series R/Evolution, is an internationally renowned fine artist, an authority on digital printing, and a respected lecturer and workshop leader. Get his enews Insights with access to hundreds of lessons at www.johnpaulcaponigro.com.

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