Rock engravings can vary in size from a few centimetres to many metres. To photograph large designs from directly overhead can be challenging. We use a method of planar mosaic imaging. This involves taking a series of smaller images and then stitching all of these images together to make up a large composite image of the entire engraving. This is similar to photographing a panorama, but instead of rotating the camera around a fixed point the camera is moved in a plane parallel to the rock surface. To ensure successful stitching, each image needs to overlap the next so that the stitching software can find how to align and join the images. Photographing a single engraving may involve taking hundreds or even thousands of these overlapping images.
Setting The Camera
The camera should be set so that the exposure is identical for each of these smaller images. The best way to achieve this is to put the camera into manual mode and turn off any exposure compensation. The focal length, ISO and shutter speed should not change over the course of shooting a series of mosaic images. If your camera can shoot RAW then this is the best option, otherwise shoot at the best quality possible, preferably with a prime lens. A zoom lens pointing towards the ground may change focal length under the influence of gravity or vibration. The camera should be kept the same distance from the rock surface as you take these images. This can be done by reverse mounting the camera under a tripod. A remote shutter release can make things easier when the camera is under a tripod. Avoid placing a foot, your shadow or a shadow of the tripod into any image as these things will prevent the stitching software from being able to join the images correctly. Don’t take too long to shoot the set of images or the ambient light may change or the angle of the sun may introduce unwanted shadows.
If the engraving has insufficient contrast to photograph successfully under the current ambient light conditions then you may want to consider using remote flash.
It is better to shoot rock surfaces when conditions are dry. If there has been recent rain and the rock face is wet you may need to use a polarising filter as a wet surface can introduce glare which can reduce detail in the photographs. Very rarely will the ambient conditions be perfect for photographing rock engravings, so be sure to allow for the local conditions and pack whatever equipment you might need accordingly.
If you shoot in RAW then you can adjust the contrast, saturation, sharpness and exposure values before you stitch the images together. Ensure that all of the images are adjusted by the same amount by making the adjustments on a single image and then copy the recipe and paste it to all of the other images in the series. If you are shooting in JPG then make any of these adjustments after you stitch the images together. Many rock engravings are very difficult to discern from the surrounding rock surface and careful post processing is important to achieve successful images.
This is a short list of the type of equipment that you might need to successfully be able to photograph rock engravings.
- DSLR camera capable of shooting RAW format
- Large capacity memory card for camera
- Tripod with reverse mount
- 50mm prime lens
- Polarising filter
- ND filter
- Remote flash
- Remote shutter release
- Spare batteries