Stacks of fun!

Close-up (or macro) photography is great fun, but when working very close to your subject it’s often hard to get everything in focus.  You lose what’s called “depth of field”.   You can increase the depth of field by making the lens aperture smaller (stopping down), but that doesn’t always give you enough that’s properly in focus.

"Blue flower: single image at f20" by Derek Gale

Here’s an example of a blue flower taken in the studio.  I used a single electronic flash to light it.  The distance from the front of the flower to the ends of the petals at the back is quite large, so even with the small aperture (f20) that this image was taken at, the petals at the back are not in focus.  I could make the aperture even smaller, but that then needs more flash power, and the image quality can degrade due to diffraction softening.

So how do we get round this?  The solution, for a non-moving subject at least, is to take a series of images where each image is focused on a different part of the subject, and then join them together, throwing away the out of focus bits.  You’re left with a composite image made up of all the in focus bits.  It’s called “focus stacking”.

So what do you need to do this?  The exposure needs to be constant so you need a controllable light source such as an electronic flash, or constant daylight.  It’s best to set your camera on manual exposure.  You also need a tripod to give good camera stability.  That’s needed to make sure the images can be aligned properly.  Finally you need some software to do the hard work for you.  I used Photoshop CS5, but other focus stacking software is available.

"Blue flower: 5 stacked images" by Derek Gale

Here’s the result.  You can see that the rear petals are now nicely in focus, and the focus is all the way through the flower.  There are 5 images, each taken at an aperture of f6.3.  I could have used lots more images with smaller focus differences, but there’s a compromise between sharpness and image processing time.   Lots more images =  lots more processing time.

As the title says, it’s “Stacks of fun”.  Why not give it a go?

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