First developed to inspect the bore of rifles and other firearms, the borescope allows the user to closely examine small, confined spaces by providing a lens system and light source that transmits images up to the eye piece. The ridge rod borescope uses an inflexible rod that is inserted into the machine to be examined. Other scopes use flexible, fiber optic material to carry images up to the eyepiece. Some come equipped with video cameras and LCD screens that display their images on a monitor held by the user.
But, suppose you want to capture the image viewed through a scope as a still photographic image.
How, exactly would you accomplish that?
That was the question one of our clients posed to us here at Joyco.
First a little research was in order. A borescope, specifically ones with an optical eyepiece, create what's called an "aerial" image, meaning the images you see through it, are not visible until your eye focuses them on your retina. This is a very difficult type of imaging device to work with photographically, since there is no image focused on surface, like a projector focuses an image on a screen.
So to complete the assignment, I had figure out what combination of lens or lenses would take the place of the human eye and allow photographs to be made through the aerial eye piece of a borescope.
Another problem needed to be solved, but it was much more mechanical.
How do you hold the borescope/lens/camera combination and still be able to point the rig in the right direction to photograph the features inside an engine that are of interest for this investigation?
Fortunately, I had some experience putting together professional camera and speciality lens supports using common hardware store items and basic metal working. Drawing on this accumulated knowledge, I was able to come up with solutions for all these questions.
Through testing, I discovered that ordinary DSLR lenses would not focus the aerial image correctly to produce a clear picture. Secondly, because of the shape of the eye piece ambient light would leak in, around the eyepiece, and degrade the image.
But then it occurred to me that a macro, closing focusing lens might be better suited for the task.
As it turned, a long time ago, I purchased a used Micro-Nikkor close focusing lens for personal use. Could that type of lens solve my problem? That lens turned out to be a God send. First, by being able to focus down to a few inches from the front element, the lens was able to produce a clear, detailed image, despite the less than stellar optical performance of the borescope itself.
Even more importantly, because the front element of the lens was deeply recessed into the barrel of the lens, the borescope eyepiece fit perfectly into the barrel of the lens without actually touching the front element, thereby sealing out extraneous light. Now we were getting somewhere!
Next I had to think of a way of holding all this equipment together. Not surprisingly, the manufacturer of the borescope, never intended the device to be used as photographic instrument, so they neglected to add features like a threaded ring for filters or other such mounting niceties.
So how do you hold all these pieces together?
Using something camera techs call a "cheese plate," I was able to make a stable rig that kept the borescope eye piece, lens and camera body all properly aligned and stable enough to allow the borescope to be positioned correctly to photograph the desired details inside the engine.
The "cheese plate" was simply a 1/4" thick piece of aluminum plate with a number of holes drilled and tapped in it, that allowed accessories to be attached to it to form a rigid unit. Usually a cheese plate is employed to hold a camera, lens, matte box, monitor, recording equipment or other devices stably as a unit so the entire rig can be either be hand-held or mounted on a tripod. Using an unusually long cheese plate created for use with Joyco's DSLR cameras and audio equipment, I was able line up everything, and create a stable camera/lens rig. Previously, I had created a number of plates at home in my garage, for various Joyco shoots, so all I had to do for this shoot was to make one to accommodate the length the borescope, lens, camera body.
Once we had a stable rig in-hand (thanks to the ever-creative Josh Bernhardt), photography of the engine went smoothly. All angles were covered and the client was pleased with the final results.
And that's what it is all about, after all.