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Foreground in focus

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Background in focus

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Two exposures combined to achieve infinite depth of field

How deep would you like your depth of field to be? 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 multi-shot exposure practices and software – by compositing multiple exposures.

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 or microphotography, 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 post-processing easier. While using a tripod always delivers more reliable results, don’t let this stop you from trying this technique hand-held, especially with simpler sequences, like those used in landscape. You may notice that In cases involving extreme depth of field, you may notice the relative size of objects may change between individual exposures. These effects will be automatically adjusted during the merging process.

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 re-access 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.

Once you have a processed set of focus bracketed exposures you can automate the process of stacking and blending them into a single file in Photoshop. (Unlike HDR and Panorama merges, you can’t make a focus stacked merge in Lightroom – currently.)

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Photoshop’s Auto-Blend Layers dialog

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Photoshop’s auto-masked layer stack

Take these four steps.

1          Using Adobe Bridge highlight all of the files you’d like to combine.

2          Go to Tools > Photoshop > Load Files Into Photoshop Layers

3          In Photoshop’s Layers palette highlight the layers

4          Go To Edit > Auto-Blend Layers, check Stack Images and click OK

You can then 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.

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Helicon Focus’ main window

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Helicon Focus’ Autoadjustment panel

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Today’s cameras (including smart phones) can create great looking HDR images on the fly, but to get optimum results it’s best to do this manually. In camera solutions render artifacted JPEGs and give you little or no control over how the results look. For optimum results, make separate Raw exposures and render them manually. While the technology at work is wizardry, this four step process is easy to practice. It’s an essential skill for all photographers.

light

+2 stops

normal

average

dark

-2 stops

1       Expose

Today’s fast burst auto-bracketing cameras combined with software alignment make hand held HDR possible. However, it’s recommended that whenever practical you use a tripod to eliminate any alignment issues between frames that might arise; it’s necessary if exposures are long.

HDR merges require multiple bracketed exposures. The goal is to produce at least one exposure with great highlight detail and another with great shadow detail. You may need additional exposures in between your lightest and darkest exposures to help smooth tonal transitions between shadows and highlights. The most common number of images used is three, because this is the default number for auto-bracketing on DSLRs. However, there is no ideal number of exposures for all scenes. Some scenes need as few as two, while others need as many as eight. In general, it’s best to have more than you need, not less. The wider the dynamic range of the scene the more exposures you’ll need. Make sure that separate exposures are between 1 and 2 EV (exposure value)(equivalent to one f-stop) apart. It’s typically recommended that you fix f-stop and change shutter speed to avoid depth of field issues, but other changes in EV will work.

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Merge in Lightroom

2       Merge

After producing multiple bracketed exposures, the next step is to combine them with software into a single 32 bit file.

Simply select the exposures you wish to include (You don’t have to use them all.) and use the software of your choice. The software you use to merge exposures will compensate for alignment and ghosting, from motion of either camera or subject. (Lightroom and Photoshop do excellent jobs.)

Rather than rushing to render this file at the same time, save it – you may want to render it multiple times.


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