How to focus stack macro photos
Load your macro shots as layers in Paint by Zaweba, Auto-Align them, then Auto-Blend with Stack images for one picture that is sharp from front to back.
Focus stacking takes three steps in Paint by Zaweba. Load the shots as layers, run Auto-Align Layers so they line up, then run Auto-Blend Layers and choose to stack the images. Paint keeps the sharpest part of each layer, builds the result with layer masks and evens out tone and colour between frames, giving one picture that's sharp from front to back.
Macro photography has a very shallow depth of field. Get close to a flower or an insect and only a sliver is in focus. Stopping the lens down helps a little but softens the picture through diffraction. The answer is to take several shots, each focused a little further back, and combine the sharp parts.
What you need
A series of photos of the same subject, each focused at a slightly different distance, from the nearest point to the furthest. A tripod makes it far easier. Paint by Zaweba is free and offline on Windows.
Shooting the stack
Set the camera to manual exposure and white balance so frames match. Focus on the nearest part of the subject and take a shot, then move focus a little further back and shoot again. Keep going until you've covered the furthest part.
How many shots you need depends on the depth of the subject and how close you are. Overlap the sharp zones generously; too few frames leaves soft bands. A still subject and no wind help a great deal.
Step by step
Load the photos into one document as layers. File > Automate > Load Files into Stack does this in one go.
Select all the layers and run Auto-Align Layers. Focusing changes the framing slightly, an effect called focus breathing, and handheld shots shift too, so alignment matters. Auto usually works well; Reposition only is fine if the camera was on a firm tripod.
With the layers still selected, run Auto-Blend Layers and choose Stack images. Paint compares sharpness across the layers and builds a mask for each, showing only its sharp parts. Tones and colours are blended so the joins don't show.
Fixing problems
Because the result is made of masks, you can fix it by hand. If a hair or an antenna is soft in the blend, find the layer where it's sharp and paint white on that layer's mask over the spot. If something appears twice, perhaps because it moved between frames, paint it out of the masks of all but one layer.
Look at the edges of the frame. Alignment can leave thin strips where not every layer covers the picture. Crop them off, or fill them.
Halos can appear where a sharp foreground edge meets a soft background. Painting on the masks or careful cloning sorts those out.
Getting a good result
More frames with smaller steps give smoother results than a few big jumps. Keep the light constant, since flash recycling or passing clouds make frames differ. And finish with gentle sharpening after the stack, not before, so the blend judges the original detail.
Other uses for the same tools
Auto-Align and Auto-Blend aren't only for macro. Landscapes with a near flower and distant hills can be stacked the same way. The tools also make panoramas, where Auto-Blend builds the seams as layer masks. And Photo Blend Layers can merge a group shot so everyone has their eyes open. Paint by Zaweba handles all of these with the same editable layers, so nothing is ever locked in.
