Effective Lighting Techniques in Boreholes, Shafts, Mines and Caves.
GeoVISION Borehole Camera Lights
Videos of boreholes provide a continuous stream of still images commonly referred to as a video or movie.
A video is much better than a single image at providing information of the borehole as continuous stream of images helps us perceive the subject better. For purposes of showing the differences in lighting techniques, we have used several single frames that were "captured" from borehole videos. While these images are not as helpful in studying the borehole as a video, they are useful in comparing different lighting methods.
Limitations of Video Photography in Boreholes
Unlike most nature photography which uses natural light, borehole video camera systems must supply their own light. This is true in boreholes, shafts, mines, caves, and other voids. By supplying the only light the photographer has a great deal of creative control -- literally painting the scene with light; however, the small size of most boreholes severely limits light placement. Most borehole camera manufactures settle for placement of camera lights (LEDs) next to the camera lens. While this location is the most economical, it produces flat images and videos with no shadows and little texture, making the video difficult to understand. This light placement also causes glare when particles are suspended in the water in front of the lens as the light bounces back into the camera.
The best photographic or video images are obtained when there is a primary light to the side or at a substantial angle to the direction the camera is viewing. Any professional photographer can easily explain the advantages of early morning or late afternoon photography and using indirect lighting and off camera flashes.
If the subject is illuminated only by the on camera LEDs around the camera, the borehole or mine shaft will appear two-dimensional and features closer to the camera will be much brighter than those farther away. By moving the light source away from the camera, shapes and forms are better revealed and the video or picture is more likely to show depth.
Off Camera Supplemental Lights
Moving the primary light source to the side is not possible in most boreholes, however when the primary light is placed above the camera, its light bounces off the borehole walls and has the effect of indirect lighting. GeoVISION offers several off camera light sources, the Dual and Quad Dive Lights and the Super Eight Light. They provide indirect light to improve videos. When these lights are used, the on camera light provides fill light to reduce the harsh shows. Sometimes, the fill light is not needed, for example, when suspended particles are in the water. Light from the LEDs around the camera bounces off these particles and goes directly back into the camera. This is a type of glare that reduces the quality of the image in several ways. GeoVISION stainless steel cameras has an on/off switch that allow the operator to turn off the camera lights and use only the supplemental lights.
The GeoVISION cameras also have an automatic electronic shutter (no moving parts) that adjust the light sensitivity of the camera the on camera lights provide fill light which in most cases improves the video; however, with many suspended particle into he water the on camera lights may do more harm than good. Using only the supplemental lights will help considerably in this situation
The camera On /Off switch allows the user to turn the LED's mounted around the lens of the GeoVISION Standard, nano, and micro cameras on or off depending on the situation.