Focus Stacking at 1:1: Sigma 105mm f/2.8 DG DN Macro Art
Focus stacking is the technique of capturing multiple frames at incrementally shifted focus positions and blending them in software to produce a final image with greater depth of field than any single frame can provide. At 1:1 magnification, where a single frame at f/8 yields approximately two millimeters of sharp depth, stacking fifteen to twenty frames at overlapping focus intervals produces an image where several centimeters are in acceptable focus. This is not achievable any other way.
The Sigma 105mm f/2.8 DG DN Macro Art for Sony E-mount or L-mount is the lens that makes this practical. At 1:1, the working distance from the front element to the subject is 13 centimeters — close, but workable on a tripod with a subject that is genuinely stationary. The lens’s linear focus motor (LF, in Sigma’s nomenclature) allows precise, repeatable focus adjustments driven either by the camera’s in-body stacking function or by manual rotation of the focus ring in controlled increments.
Sony cameras implement in-body focus bracketing: set the step size and number of frames, lock the camera on a tripod, and the system automatically shoots the sequence at incrementally changed focus distances. Import the RAW stack into Adobe Photoshop (Edit > Auto-Align Layers > Auto-Blend Layers > Stack Images) or Helicon Focus, which offers more control over the blending algorithm. Helicon’s Method B (Weighted Average) handles the smooth tonal transitions in organic subjects — insects, flowers — better than hard-edge blending methods.
The limitation is subject motion. A leaf in any air movement will produce alignment artifacts no software can cleanly correct. Windless conditions, or shooting indoors with still subjects, are the practical domain of this technique. Living insects require extremely fast stacking sequences — some photographers shoot ten frames per second and cull to the frames where the subject held position.
The Sigma 105mm Macro Art is optically excellent and mechanically reliable enough to be the center of a repeatable stacking workflow. The images it produces at 1:1 blended from twenty frames look like they were made with a microscope.