Macro photography - part 5: Focus bracketing and stacking

Robber fly images stacked into a single photo.  Zerene Stacker software was used.

Photo stacking is a way to get more depth of field than what can be achieved through aperture alone.  Even if a really small effective aperture (f/45 for example) will get everything in focus, a photo will come out better if it is stacked.  The reason has to do with a lens' best aperture setting for sharpness.

There is a sweet spot in every lens - an aperture where sharpness is at its maximum.  This tends to be one or two stops past its minimum value.  For a macro lens with a minimum aperture of f/2.8, that may be at f/4 or f/5.6.  As the aperture gets smaller there are more diffraction issues that reduce image sharpness.  The advantage of using a wider aperture is an increase in sharpness; the disadvantage is that there is less depth of field.  Stacking offers a way to get the best of both worlds.

The best way to do stacking is to use a tripod for your camera setup and mount your subject in a well lit, easily accessible place.  If the subject is alive it will likely hamper your shots as all the images have to be the same.  There is a way to remove ghosts when stacking, depending on the program.  I am never fond of killing creatures, with the possible exception of mosquitos.  However, if you want to do stacking well, the creature generally has to be dead.  Some things, like fungi, minerals, and certain creatures (spiders in a web for example) will be plenty cooperative.

I use a tripod for my camera and a monopod for the subject.  The monopod has a ball head on it to allow me to move the subject in any position I want.  I may also include a background; sometimes it is just a white paper plate so that I get the subject without any extras.  That's what I did in the above photos.

How many photos are used?  That depends largely on how much depth of field you need and the base depth of field for any one shot.  You don't want to go edge to edge, rather you can overlap focus by 50% or so to ensure the greatest quality.  I did 7 in the above photo (4 are shown), but I have seen stacked images using 300 or more images.  When the depth of field is practically non-existent, you need more images, especially if the subject has any depth to it.

The trick with stacking is to make tiny advances in point of focus.  This can be done by hand, but it is at best a guess and likely to miss a few areas.  You can mount your subject or your camera on a rail system.  There is even motorized rails that automatically advance.  You can also set it up so that the system shoots an image, advances, shoots another image, and goes on repeatedly without your input after setup.  You can imagine that such equipment is pricey.  I would recommend it only for individuals that are passionate about precision macro photography.

Lighting is a big issue in macro photography.  I will do a blog on it later; the information there will apply to stacking.

Thanks for reading.

Eric Svendsen     www.ericspix.com