1) The first step is to consider your subject. What is it you are trying to study? Whether you are trying to capture cracks, dents, minute changes in topology, or macroscopic changes in topology, the absolute smallest detail you need to capture can be no smaller than 25 pixels. Taking your camera’s resolution into consideration, calculate if the details you are trying to study are at least 25 pixels. This can be done by taking test shots, then bringing those test shots into a photo editor such as Photoshop, or even a free paint program such as Gimp or Microsoft’s Paint. All of these programs have the ability to measure distance in pixels.
If there is not sufficient detail, either move closer to the subject, change lenses, or do both so that optimal resolution is achieved.
2) Once your distance from the subject and camera lens are chosen, a horizontal line of known length needs to be placed in the frame with your subject. This allows for accurate distance measuring and scaling in the 3D mesh. A great way to do this is to place Dennison Dots equidistant and level all the way across the subject. Not only do Dennison Dots placed onto the subject help in scaling and measuring along the mesh, but it also helps in the capture process by giving visual cues for the amount of distance to move along the subject. For this to be effective, the distance in between dots should be roughly one third of the total horizontal distance of your photo.
3) The distance from the subject to the camera and the distance in between your Dennison Dots should now be established. Pick a line that will run the horizontal length of your subject and place the Dennison Dots along this line. Make sure that these dots are not only equidistant, but are also perfectly level.