Why Focus Stack?

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Today’s Question: Why would you even focus stack in the first place? This is the first I’ve ever heard of this process. And why is an app like Helicon Focus advisable?

Tim’s Quick Answer: Focus stacking enables you to achieve greater depth of field when it would otherwise be impossible with a single photo. Focus stacking is especially helpful in macro and closeup photography, but can be helpful in other scenarios when you are focusing relatively close to a subject.

More Detail: Today’s question is a follow-up to a recent question about assembling HDR images that include focus stacking. Focus stacking is somewhat similar in concept to exposure bracketing. The difference is that with focus stacking you are essentially bracketing the focus setting, rather than the exposure. You can then assemble the “bracketed” focus captures into a single image with extensive depth of field.

When you capture the original images for focus stacking, you adjust the focus for each exposure. For simplicity, let’s assume you’re focusing on a close subject and even stopping down to the minimum aperture size you achieve one foot of depth of field. Let’s further assume you want to achieve five feet of depth of field.

You could start focusing at the very front of the subject. Then adjust the focus manually to shift the depth of field further away from you, overlapping with the depth of field from the first shot. Repeat this process until you have covered the full range of desired depth of field with your focus stacking captures. With this example you might initially assume that to cover five feet of depth of field you would need five photos that each of one foot of depth of field. In reality, you would need more shots, because you need to overlap the depth of field.

After capturing the focus stack images, you of course need to assemble them into a single image that includes the extended depth of field. It is possible to assemble the focus stacked image in Photoshop, by my experience has been mixed (but mostly not great) using Photoshop to assemble a focus stack. I have had excellent experience, however, with Helicon Focus, which you can find here:

https://timgrey.me/helicon