One of my biggest challenges is maintaining a constant range to the subject when taking a macro panorama.
This comes up, for example, when photographing tree stumps for dendrochronology. There is a large tree stump and the photographer needs to take a mosaic of macro shots to document the face of the tree stump. So, for example, the tree stump might be 30 inches in diameter and photo will cover a 5-inch square area or so. Therefore, there might be around 20-24 different shots total which all must be stitched together to get a master image of the entire stump.
The problem arises as to how to keep the range to the stump constant. If the height of the camera above the stump surface varies even a little, then the apparent ring sizes will be different which is bad. Using stands or rails does not work because often the stump will not have an even surface and the ground will be very uneven, so trying to use any kind of fixed structure is not really feasible. Also at the edges of the stump there is no place to set the stand anyway. Even assuming I spent hours setting it up, a 4-way 40 inch precision macro focusing rail system would cost like $10,000 which is way out of budget for me. Also, these stumps are sometimes in remote areas, so simply carrying a 40-inch rail system up some mountain is out of the question.
Ideally, what I think is the right type of solution is to use a set of registration targets and then adjust the camera so that the targets have the exact same dimension in each frame, but I do not know exactly how this is done. How do I know that a dimensional target is the same size in different shots?
Currently I use a D200 with a Nikon AF Micro-NIKKOR 60mm f/2.8D lens.