|Aerial Photography From Your R/C Model|
This article is not intended to be an in-depth scientific analysis of vibration isolation methods. Instead, it's a guide to some basic concepts that will help to give you a "gut feeling" for how such systems behave.
Vibration - The Photographer's Curse
While it is possible to reduce blur through the use of high shutter speeds, the result is less latitude with choice of film speeds and aperture settings. Why be forced to use "fast" film that tends to be more grainy and have less contrast? Why be forced to use a wide-open aperture setting that will reduce sharpness? (A lens generally performs best a few stops back from maximum aperture.)
On top of all of this, a vibration, if bad enough, can still blur a photo taken with a high shutter speed. It can also damage your camera. The conclusion: vibration control is imperative!
A Closer Look
But you want to do aerial photography from your model, right? The necessary steps to control vibration depend on what type of vibration is being generated. If it's a plane, we are contending with vibration from the engine and propeller (which obviously should be balanced as well as possible). This is a fairly high frequency vibration. At a throttle setting of 12000 RPM, this equates to 200 Hz (cycles per second).
The situation with a model helicopter is more complex. The vibration sources are engine, tail rotor and, worst of all, the main rotor. In a "sixty" size helicopter, these would be in the vicinity of 240 Hz, 150 Hz and 27 Hz respectively.
You can see that the main rotor is by far the lowest frequency source. Is this significant? Yes, because low frequencies are the hardest to kill. We can all relate to the problem of getting to sleep when the someone in the building has their hi-fi cranked up, and all you can hear is the bass. Only the bass gets through, because low frequencies are better able to overcome the inertia of mass - in this case, the walls of your room.
To summarize these points:
Applying This To Our Situation
Soften the mount further, and you'll get to the point where the camera does not feel the engine vibration at all! The vibration movements are happening too quickly for the soft mount to transmit them and overcome the camera's inertia.
If it's a plane, then all well and good. A helicopter, as we've mentioned, has additional lower frequencies. We have to support the camera with a soft enough mount that will filter out all the frequencies down to that of the main rotor. This requires a softer mounting method than a plane.
A firmer mounting method will be acceptable, thanks to the high mass and resultant inertia of the system. The extra firmness will also be necessary to prevent the system from swinging excessively (like the brick).
Your next question is probably "Well, how do I know if it's too soft or too hard?"
It's easy to answer. Make it as soft as you are comfortable with, given the need to restrict excessive movement. As a guide, you probably wouldn't ever want your camera equipment to move more than an inch in any direction.
The actual design will depend on how much control you wish to have over your camera. For example, if you only want a forward-looking camera, with no pan or tilt, you obviously have a simpler task.
I have even seen cameras taped to aircraft with foam wedged in between! However, such a crude arrangement may carry the risk of losing the camera, or causing injury. This is a good time to point out a safety concern: any system where a camera is attached to a model aircraft must be made to be absolutely safe. It must be impossible for the camera to be dropped. This will often involve a back-up support method such as a safety line.
When weighing up different options, I would be looking at simplicity, elegance, ease of construction, and how much the assembly will weigh. As long as you can keep it safe and reliable, lighter is always better!
Next time I'll be experimenting with an unusual method of getting your camera airborne.
Contributed by Richard Shelton at HiCam.
Web Site: HiCam Aerial Photography
(These articles first appeared on the Hi Cam web site
and have been reproduced with the owner's permission).