Camera Vibration or "Don't shake it like a polaroid picture"

A very valid concern of filming by helicam is - how smooth can/will the resulting images be? While a blog is obviously not the best venue for an in-depth technical discussion, one cannot properly address this particular issue without at least briefly touching on some of the technical aspects. Vibration is commonly described as the periodic displacement (movement) of a body (camera in this case) from a position of rest. The vibration frequency (period) is defined as the number of cycles (times body moves from rest to each extreme and back to rest) and is often expressed in cycles per second (CPS). Amplitude is defined as the distance that is traveled during each vibration cycle. Velocity is another term used to measure and analyze vibration but we will leave that another discussion.

All helicopters, both large and small, generate a wide range or spectrum of vibration frequencies as a result of all the various rotating parts. To complicate matters further, unwanted camera movements can result that don't fit the standard definition of vibration as they occur randomly due to abrupt movements of the helicopter airframe and/or aerodynamic forces and wind buffeting for example. The latter type of movement can usually be reduced or virtually eliminated by a well designed mechanically or electronically stabilized camera mount or gimbal. At high forward speeds, the aerodynamics of both the camera, mount and helicam airframe all come into play also. Okay, enough of the technical stuff already!

The challenge for the helicam builder is to design and build an airframe where all the rotating components are as perfectly aligned and balanced as humanly possible. The problem here is that most of the commonly produced components do not have nearly the exacting tolerances required to achieve rotational nirvana. So to accomplish this lofty goal, a combination of precise measurements, material selection, structural design, damping and vigorous static and dynamic balancing is required.  Even further, once achieved, the final design must be robust enough to hold the tight tolerances required and keep operating smoothly after numerous flying sessions. Considering this, it is easy to understand why a helicam builder/pilot might want to avoid extremely high risk situations and would likely possess a particular brand of hatred for heavy-handed baggage handlers! 

Each helicopter airframe produces its own unique range of vibration frequencies, displacements and amplitudes. If you built two identical airframes, side by side, the resulting vibration signatures produced by each would be similar, yet not identical.  Complicating matters further, not all camera types respond to vibrations the same. 35mm film cameras are far more forgiving in this regard than video cameras for example. Conversely, SD cameras are more forgiving to vibration than HD cameras. This is due to many factors such as sensor type, image stabilization along with camera size, weight and construction. Another example is CMOS sensors do not respond well to high frequency vibrations as CCD types and can often display the unsightly "jello" effect as a result. Multicopters are particularly prone to rolling shutter artifacts generated by the numerous high rpm electric motors and their inherent tendency to produce either non-synchronus or sub-synchronous vibration due to the interaction between the large number of nearby rotating motors and propellers . This does not mean that they are unsuitable, it merely means a higher level of tuning is required by the designer/builder to make them work. It should become quickly apparent that not all cameras would perform equally well on all types and sizes of helicopters. Our particular experience has shown that the smaller the helicopter, the more high frequency vibrations will be produced. This presents a very real challenge if a CMOS based camera is being used.

Gimbal stabilization can be accomplished by means of electronic gyros, mechanical gyros, inertial management units or by some combination. These can provide either active or passive stabilization, or some combination of both. If the camera movement is not to fast or severe, most unwanted, low amplitude camera movements can be removed in post using stabilization software. Some popular examples are Smoothcam in Final Cut Pro, Warp Stabilizer in Adobe Premiere Pro and Mercalli. For advance stabilization there are also motion trackers such as Syntheyes and the Foundry plug-in for After Effects. Use of post stabilization comes at the expense of some loss of resolution and image cropping but if used in small amounts it can be very effective. This is another huge advantage of using ultra high definition cameras like the Red Epic for aerial filming as there is so much resolution head room. Currently this type of stabilization does still have difficulty removing high frequency vibrations, especially using wide angle lenses. This problem can be somewhat corrected however by removing lens distortion in software.

The most exciting advancement in the area of camera stabilization is direct drive gimbals. Advances with this technology are currently moving at near light speed. Very soon you will be able to shoot close range aerials, full size aerials and ground level steady cam type shots, all with the same mount.

The bottom line is however, the less vibration the helicopter produces - and the camera sensor sees, the better! This is why Perfect Perspectives uses only the most advanced vibration monitoring/dynamic balancing equipment available to ensure smooth footage. This is not referring to the vibration app on the iphone or vibration logs off of flybarless controllers here, but rather industrial grade, precision FFT vibration spectrum analyzers, multichannel accelerometers and laser alignment instrumentation.

For more info please visit http://www.perfectperspectivesaerial.com