These notes are from a short talk given to the Nelson Camera Club, an introduction to the technique of ‘focus stacking’.
‘Focus Stacking’ is the term used when we combine several photographs in an attempt to get more of the final image really sharp. It’s often used in macro photography, where the depth of field is very often quite shallow. The example I’ve chosen however is an image of a relatively large object, “ Lantern Fish I ” by artist Bruce Derrett. Overall, it measures about 50-60 cm from front to back.
That initial image was taken at f/8 with my AI-S 105 mm f/4 Micro-Nikkor lens, with the camera mounted on a tripod. Focusing and exposure were done on manual, using ‘Live View’. I focused on the closest part of the artwork, the “teeth”. They’re nice and sharp:
but the tail is definitely not:
Next I took another six images, each one with the focus point further back.
If we look at the last one in that sequence, you’ll see this the tail is quite sharp
but the teeth are very blurry
Next came the magic. I loaded all seven images into a software package (Helicon Focus, see below for link) , clicked on “render”, and watched an image gradually appear. It was sharp throughout:
(The image has been worked on a little in Photoshop, to remove the base and lighten the background. It is available as a limited edition, Giclée print on 13 x 19 in Epson Ultra Smooth Fine Art paper, complete with certificate of authenticity. Contact me here for further details.)
Macro work (some links)
For macro work, it is usually advisable to move the camera or subject, not the focus ring on the lens. I use a simple focus rail by Manfrotto:
For fine, precision work others have created some wonderful rigs, such as the ‘Bratcam‘ by Chris Slaybaugh. Coarse adjustments of the camera and subject position are handled with a pair of microscope focusing blocks, while a precision linear translation stage is used for the actual exposures. With such rigs it is possible to use a microscope objective (lens) which, while extremely sharp, has a depth of field of only 10 microns or so. 2000 exposures would be needed to cover a subject 10-20 mm long!
If you would find that too tedious, then the ‘Stackshot‘ is for you. It uses a microcomputer and stepper motor to automate the whole process.
You can find many more examples of macro rigs, try searching for “macro rig”, or “extreme macro rig”. The Photomacrography forums are a wonderful source for high magnification macro work.
Software
Once you have the sequence of images, there are various applications which can be used to combine the sharpest parts of each image into one composite, overall sharp image.
It’s possible to do it in Photoshop (although I’ve never tried). Here’s a tutorial.
Wikipedia has a good list of the available software. Some of them are freeware, although I haven’t found any free software that matches the bought ones.
Zerene Stacker seems to be the one preferred by serious focus stackers.
Helicon Focus is the one I use. It has a 12 mth trial, with the option to upgrade to a permanent licence at a cost only a little more than if I had bought the permanent version straight off. I liked that approach.
Addendum: Addtional notes on Photoshop
A few days after these notes were posted, Daniel Wong sent an email to club members with more detail on the use of Photoshop for focus stacking. Because emails eventually seem to disperse, I have reproduced his note here:
There are endless youtube videos and articles on the internet about how to achieve focus stacking in Photoshop. Do take the time to look at them. Briefly, there are two main ways to achieve focus stacking in Photoshop, either through Photoshop’s automatic process or by manually blending images.
For the first method which is simpler load your separate photos as layers into Photoshop, select all your layers in the layers panel, then select Edit, then “Auto-align layers” and use the “Auto” option. Then select Edit, then “Auto-blend layers”, and use the “stack images” option with “seamless tones and colours” ticked.
The second method is to use masks to mask in sharp areas of your image, which can be tricky if you have a really thin depth of field and have lots of images to combine, but allows greater control over the blending process.
Daniel Wong March 2015
A few cautions for those not using the ‘CC’ version of Photoshop:
I believe the ‘auto-align, etc’ facility was only introduced to Photoshop in CS4 (and according to some, it only became usable in CS5). People (like me) still using CS3 will be out of luck and forced to use layers and masks.
There are some interesting comparisons of the merits of Photoshop versus the dedicated applications listed above. It seems that for most situations apps like Zerene Stacker or Helicon Focus are faster or give better results, but not always. For some images (e.g. those with changes in alignment or exposure within the stack), Photoshop can give a better result. Here are some links you might find interesting:
http://www.dennisgoulet.us/focus-stacking-image-comparision/
http://photography-on-the.net/forum/showthread.php?t=1075776
Macro example
Finally, here’s an example of the technique applied to a smaller object. This is taken with my 105 mm Nikon AI-S Micro lens. It’s a composite of 25 images, taken at f/4.
