These devices are useful for looking into crevices and cavities inside trees. They are essential for inspecting trees for the presence of bats (in accordance with the laws applying to bats).
They consist of a cable (obedient or non-obedient), a handle assembly which houses the batteries, light source and focussing control. They are available in different lengths and the serious bat inspector will need a cable length of around 1m.
The 'obedient' term refers to the cable type, where it can be moulded into a shape and it remains fixed. Non-obedient is just as flexible but it will always try and spring back into a straight state. Both types have their uses for differing situations although 'obedient' is most useful if using a longer cable length.
The scope cable consists of a bundle of fibre optic cables with a glass window at its tip. The fibre optics are organised so that light, from a bulb housed in the handle assembly, is sent down the outer ring of cables to illuminate the crevice. The viewing takes place with the inner fibre optic cables where the image is received and focussed using the eye piece. The system works very well and is best when using a higher power halogen light bulb.
In use I found the tip of the cable occasionally became clogged with dirt, moss etc. This would need cleaning carefully with a match stick or similar as the tip of the cable is actually enclosed in a small recess. The light operates with a trigger button to save battery life.