Stack for sharp­ness

Get the ul­ti­mate depth of field in your out­door shots: Rod Law­ton shows how to stack a se­ries of frames with dif­fer­ent fo­cus points

NPhoto - - Contents -

Don’t risk dif­frac­tion from a tiny aper­ture, try fo­cus stack­ing in­stead

If you want the max­i­mum depth of field, or near-to-far sharp­ness, in your out­door shots, the usual ap­proach is to set a very small lens aper­ture. How­ever, while this does in­crease the zone of sharp­ness in your pic­tures, there is a draw­back. At aper­tures of f/16, f/22 or smaller, the im­age de­tail starts to soften due to ‘dif­frac­tion’ ef­fects.

There’s no way round this. It’s caused by the way light rays bends as they pass through small aper­tures. In the days of film it was less ob­vi­ous be­cause the re­solv­ing power of film was lower than the dig­i­tal sen­sors we use to­day, and it was harder to mag­nify im­ages to the lev­els at which we can view them at on a com­puter screen. Now, though, the drop in sharp­ness at small lens aper­tures is quite ob­vi­ous. To get the best qual­ity with to­day’s cam­eras and lenses, you don’t want to shoot at aper­tures smaller than f/11 if you can avoid it.

To solve the prob­lem of dif­frac­tion, here’s a tech­nique bor­rowed from the world of macro pho­tog­ra­phy. It’s called ‘fo­cus stack­ing’, and it means tak­ing a se­ries of shots with the lens

Dif­frac­tion is caused by the way light rays bend as they pass through small aper­tures… To get the best qual­ity with to­day’s lenses you don’t want to shoot at aper­tures smaller than f/11

fo­cused at dif­fer­ent dis­tances, then com­bin­ing them in Pho­to­shop.

In macro pho­tog­ra­phy, fo­cus stack­ing is a painstak­ing process be­cause the depth of field is very shal­low at short fo­cus dis­tances – you may need to take as many as 50 shots to make sure ev­ery part of the sub­ject is sharp in at least one of them. But when you’re shoot­ing out­doors, you’re fo­cus­ing on ob­jects fur­ther away. As long as you use a medium aper­ture of f/8, the depth of field for each shot should over­lap enough to leave no ‘fo­cus gaps’ in your fi­nal pic­ture.

Our fin­ished pic­ture is made up of just four frames. They’ve been blended us­ing Pho­to­shop’s au­to­matic Pho­tomerge and layer blend­ing tools – there’s re­ally noth­ing to it.

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