![]() ![]() This, factored in with the previously-noted requirements for focus stacking, resulted in 288 total raw images being shot of the piece. Since a block of kneadable eraser was used to support the lithic first by its base, then by its tip, separate 360-degree rotations were conducted for each object orientation to guarantee full look angle coverage and to avoid occlusions caused by the support. This resulted in a total of 144 shots per complete 360-degree spin which were derived from 36 incremental 10-degree rotations of the lazy Susan. For lithics this small and in the shape of thin projectile points, 4 shots per bracket were normally captured. See the above illustrations for one such example. To date, test objects have included those that have measured as little as 2.71cm across their longest dimension. These were then eventually imported into Agisoft MetashapePro photogrammetry software where 3D data was created from the focus-stacked 2D TIFFs. The resulting composite images created by the program were saved out as TIFF files. Its consistent alignment and blending abilities plus its capacity to work in conjunction with Lightroom where camera raw files were initially organized by brackets and batch edited were key attributes in Photoshop's favor. Following each completed series, I would then manually rotate the object 10 degrees on the lazy Susan and commence yet another bracket from the controller.Īfter testing both Photoshop and Helicon Focus, I chose Photoshop to focus stack each subsequent focus-bracketed series. From that point on, I could shoot each successive focus bracket by simply hitting the touchscreen's start button. Once completed, the controller was finally able to automatically calculate and display the resulting number of steps required to best meet all entered parameters. Next, the beginning and end positions of the series were assigned using the controller to move the Canon 5D III along the rails while monitoring the camera's live view for correct focus through a tethered laptop. This value was then converted into millimeters and entered into the Stackshot 3X controller's distance (of rail travel) setting. In turn, the calculated depth of field was divided by 2 to estimate 50% coverage. In-focus overlap of roughly 50% between adjacent images is a good initial guideline for creating a successful focus stack in post-processing. This combination of factors works against the straightforward capture of sharp, high resolution images of small objects that could potentially serve to create richer photogrammetric geometry and texture. And most camera/lens combinations eventually become diffraction limited when stopped down beyond a certain aperture. Generally speaking, depth of field becomes shallower as one shortens the camera-to-subject distance. First author, Samantha Porter, has also produced an excellent three-part video series that goes into extensive, articulate detail on the specialized post-processing that is required of the raw data acquired from such a system. With this setup, I have been further customizing a photogrammetry technique for small archaeological lithics that I initially encountered in the 2016 paper, A Simple Photogrammetry Rig for the Reliable Creation of 3D Artifact Models in the Field: Lithic Examples from the Early Upper Paleolithic Sequence of Les Cottés (France). A Canon 5D III, my current backup camera, sits atop the Manfrotto head and is mated to a Zeiss Milvus 50mm f/1.4 ZE lens. I've attached the macro rail to a Manfrotto 405 3-Way, Geared Pan-and-Tilt Head that I screwed onto a spare tripod that I normally keep behind the seat of my truck. The resulting kit features an inexpensive popup light tent, an old lazy Susan turntable, and a Cognysis 3X Stackshot macro rail package. In addition, I was also able to checkout a small assortment of gear that I thought I would combine with my own resources at home to create a purpose-built photogrammetry rig in the basement. Small object photogrammetry rig Woodshedding in a basementīack in March during our last on-site work week before the COVID-19 shutdown at UConn, I shot and took with me as much useful raw image data as possible from our lab's automated capture system for later photogrammetric post-processing. ![]()
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