Focus stacking

Blend sharp parts of close-ups to extend depth of field

Although the smallest aperture available on a lens – such as f/32 on Canon’s 100mm f/2.8l IS USM macro lens – will give the maximum depth of field possible, this doesn’t translate into the sharpest pictures.

Fine details and edges in an image will appear soft due to diffraction. This is where a larger proportion of the light rays entering the lens are bent out of shape by the edges of the small aperture.

Even then, the smallest aperture may not give you enough depth of field to cover all of the subject you’re photographing. To get around this problem, macro photographers use a ‘focus stacking’ technique to combine the depth of field from several images. This process involves taking a sequence of pictures from the same position, but with the lens manually focused on a different part of the subject in each shot. The separate images are then blended in specialist focus stacking software or in photo-editing software such as the renowned Photoshop.

The trick with focus stacking is to adjust the focus position in small increments so there’s enough overlap of the depth of field between each frame. Using the x10 magnified Live View image can help with see where the band of sharpness falls as you adjust the focus.

To combine the images in Photoshop, use File > Scripts > Load Files Into Stack (Tick the ‘Attempt to Automatically Align Source Images’ box). This loads each image into separate layers in the Layers Palette. Now select all the layers and use Edit > Auto-blend Layers, setting Stack Images as the Blend Method.

This technique requires some practise, and it’s only a viable option for inanimate or stationary subjects.

Be prepared to shoot lots of pictures and leave some overlap, or you’ll get soft spots appearing in the middle of an area that should be sharp

the magnification of the leaf changes as the focus is moved from the front to the back. Bear this ‘focus breathing’ in mind when you compose Final Back focus

Focusing on the front of the leaf sees sharpness drop off before reaching the back. this is even with the depth of field offered by aperture f/16 Front focus

if you shoot in raw, you can change picture styles in DPP. if you shoot in JPEG, you cannot