Sunday, 13 September 2015

Focus Stacking

FOCUS STACKING
by John Nichol

DEPTH OF FIELD. The area of the “shot” that’s in focus.


As you know; the closer you get to a subject with your camera the shallower the depth of field. When you move in extra tight (macro shots) the depth of field can become very shallow.
Shallow depth of field can be good if you are looking to highlight a subject, a particular spot or small area of the subject with the rest in soft blur, but if you want a larger area of the subject in focus, depth of field can become a big issue.
THE ANSWER TO THIS IS FOCUS STACKING


Focus stacking simply put is a technique that combines multiple shots of the same subject, varying the focus point (in even steps) with each shot, from the closest point (first shot) to the furthest point (last shot), then combining the “focus area” of each shot into one pin-sharp photograph of the entire subject.
This technique can be used from landscapes, combining two or three shots, up to micro photography of microscopic subjects with several hundred shots required!

“Stepping” along the focal plane can be done manually or the camera focus can be driven with software from an attached computer tablet or smart phone, or for extreme close work the camera can be mounted on a macro rail and driven (moving the camera not the lens) by a powered “stepper”, this can take the focus steps down to very precise increments as little as  0.01mm or even less with custom built “steppers”.
I use Helicon software. Helicon Remote to drive the lens and Helicon Soft to combine the “stack” into one shot.

The hardware used can be many and varied; Macro lenses deliver great detail, but I achieve even better results using Macro and various other lenses (depending on what I am looking for) with Kenko “powered” lens tubes. These are lens mounting rings (no glass involved) that moves the lens further away from the cameras sensor; this reduces the minimum focusing distance of the lens allowing you to get closer to the subject while still maintaining focus (and/or increasing magnification). The set comes with 3 tubes-12, 20 and 36mm, they can be used individually or combining any two or all three.
They have the necessary connections to allow the camera to maintain normal lens control (you can get cheaper ones with no electronic connections but you can only adjust the lens manually). Lens tubes are also a great inexpensive way of converting any lens into a macro lens for normal field work.
Some of these tube/lens combinations in my opinion outperform dedicated macro lenses.

Another method that allows even closer shooting is a technique called reverse lens macros, Using a lens mounted to the camera in reverse (with a reversing ring)
A lens focuses light from the subject far away; the resulting image is much smaller and can be recorded by the sensor, when you reverse the lens the opposite occurs. The lens magnifies what it sees, resulting in a very large reproduction of a tiny subject.
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You can take this one step further using a coupling ring to attach your reversed lens to the front of another lens. By mounting a lens to the camera in the normal way (this is the primary lens) then mounting the reverse lens (the secondary lens) to the front of the primary lens you increase the magnification power dramatically, this also maintains the benefit of camera control over the primary lens for focusing.