Focus stacking by Heather Angel
Focus stack of African glory lily (25 frames)
If you have struggled to gain extra depth of field you need for some three dimensional shots, have you considered focus stacking? This a perfect way for revealing fine details. I began taking stacks three years ago and have done hundreds.
While it is possible to take a stack outside, by refocusing the camera slightly further away for each shot, without a focusing slide it is difficult to gauge the distance between each shot remains constant. This is why I prefer to work indoors and mount the camera on a focus slide / rail.
Focus stack (21) of gentian taken in the field with a focus rail
For a perfect stack ensure the following:
• manual focus is selected
• subject is static
• lighting is constant
• camera is advanced in fixed increments
Essentially mount the camera on a focus rail. I use the Really Right Stuff Macro Focusing Rail but cheaper models are available; you just need a 2-way one which moves forwards and backwards, not a 4 way one. and focus manually on the nearest part of the subject. The camera is then moved forward at equal intervals so a series of focus slices are taken. Decide before you start whether this is ½ or a full turn of the focusing rail advance knob and mark it with white adhesive tape in two places so it is easy to judge a full turn and half a turn. In essence it is a scaled down version of a CT scan. The number of frames needed will depend on
• the magnification used
• the depth of the subject
It can be anything from 10-40 frames and my record is 72 for a very deep tubed flower!
Common toadflax focus stack (33)
When you get towards the end of the stack, carefully check (by enlarging the image on the camera’s LED screen) that the last essential part is sharp. This is important for flowers which have pockets at the back. After downloading, the stack of partially focused images is blended into a single focused image using a software programme
Screen grab of the chocolate vine focus stack in progress. Image numbers on left, left image being added to stack. Right image shows stack building up.
Two more things to remember before you start
• check the camera battery is fully charged, because you may not be able to remove the camera easily once it is mounted on the rail. If so the stack will then have to be aborted
• check if using a flash it does not need recharging because this could upset the set-up too
A word of warning – focus stacking can become very addictive!
Completed focus stack (22) of the chocolate vine (Akebia) – a shrub from Japan and China
© Heather Angel 2013