When shooting macros, particularly when using a macro lens on a DSLR at anything approaching wide open, depth of field may be less than a centimeter. Even at higher apertures like f8 or f11 depth of field can be extremely shallow.
The cure for this is a technique called stacked focus. Basically, you focus on various parts of the image, moving from closest to further way, and shoot a frame for each. Then back in the computer you “stack” these images to form a single, in-focus image.
- You MUST use a tripod
- You MUST use manual mode and use the same exposure values for each image in the series (you can cheat on this, but you risk the camera doing something stupid)
- You SHOULD shoot in RAW for best results
- The subject MUST be absolutely still. Any movement at all will ruin your results.
- In general, more shots in a stack will give better results than two or three. Just make sure some other part of the scene is in focus for each exposure.
Photoshop has an automated routine to help with the stacking process. Here are instructions on how to do it. NOTE: I didn’t write these, and I haven’t been able to find out who did., so if you read this, whoever you are, let me know so I can give credit where it is due.
HOW TO STACK
- With the camera on a tripod so it doesn’t move, shoot a number of frames using the same aperture setting but with different parts of the image in focus. Try to make sure that everything you want to be in focus is in at least one shot.
- Process the images in Lightroom or Adobe Camera RAW (ACR) using the same settings for each one, and load the photos shot at different focal points into Photoshop as a single layered document.
- In Photoshop, in the Layers Palette, select all the layers and choose Edit > Auto > Align layers to make sure all the layers are in alignment (even a tiny amount of movement on the tripod could ruin the focus stack).
- In the Auto-Align dialog, make sure to choose Auto as the projection method.
- To blend the images with different points of focus, choose Edit > Auto-Blend Layers.