In macro photography we are supplied with a variety of components for fine-tuning focus. This equipment includes focus slider rails and built-in sliders as part of a bellows. All of these devices facilitate changes in focus by moving the camera closer or more distant from the subject.
All of these components work quite well; some better than others. A well-made slider (above) can provide infinite adjustments in focus with extremely small changes in distance. These are ideal for gross specimens or single shot macro images.
Bee head. 53 images stacked in Helicon Focus. Nikon D2Xs, 50 mm flat field EL Nikkor lens on bellows, two SB-800 flashes, tripod. Image magnification in camera: 1.6X.
However, when enhanced depth of field of tiny subjects is required through focus stacking, moving the camera may not be the most ideal method of changing point of focus. With very small insects like the bee above for instance, many exposures–perhaps 50 or more– must be produced over a distance of less than one centimeter.
Several problems are presented. First, the mass of the camera, bellows, and lens assembly is great. Moving it smoothly and accurately may not be possible. Second, the focusing rack and pinion may have coarse threads, not suitable of minute adjustments. Further, the camera, bellows and lens combination when moved is subject to unwanted vibrations. The answer therefore, is to move the subject, leaving the camera solidly stationary.
Macro subjects like those encountered for focus stacking are most frequently tiny and present no above mentioned problems. They are small, lightweight and can be easily and smoothly moved. And making repeated movements at uniform dimensions is practical. All this suggests that moving the subject instead of the camera is an ideal solution.
In my photography, I use two devices. For single shot macro I have converted an Olympus microscope stage for an X-Y-Z motion platform in the image below. It has a movement of 3 inches in left-right and fore-aft directions and a vertical movement of just under 1 inch. In addition, it has a 2 x 3 inch hole for sub stage illumination. All movement controls are under the stage so they are perfectly out of the way.
For focus stacking I use a single-axis micrometer linear positioning stage. Movements are possible along the lens axis for focus stacking in uniform increments as small as 0.001 inch. The movement for this stage is only one inch, but that is more than adequate for most focus stacking tasks. To center and align the subject, I use the gear head on my heavy duty Gitzo tripod. As illustrated in the photograph below, everything is locked down tight. Consistent, vibration-free images are possible with this set-up.
For the ultimate in focus stacking, a motorized linear positioner like StackShot® by Cognisys makes life easy. The price is affordable if a lot of focus stacking photography is required. Even with the StackShot it still makes perfect sense to move the mole hill not the mountain!
© 2013 Brian Loflin. All rights reserved.