Hi
Some years ago, I performed a series of practical tests using a set of Celestron vibration suppression pads (VSP's) to:
- better understand how they perform and;
- measure their contribution to suppressing vibrations for visual observing.
APPROACH:
A red LED was observed to oscillate in a Vixen ED 102mm f9 refractor using an illuminated reticule, (6 concentric circles), whilst a tennis ball suspended on a fixed length of string was made to strike the focuser under controlled conditions.
- The tennis ball was made to strike the focuser.
- The LED was initially displaced to circle 5 in the illuminated reticule.
- Two measurements were taken for each strike.
- Measurement 1 - the time for the LED image to stabilise within circle 4 was taken.
- Measurement 2 - the time for the LED image to become completely stationary was taken.
CONCLUSION:
The VSP's had no discernible effect on the amplitude of the displacement.
However, the VSP's significantly reduced the dampening times.
See the results and methodology that follow, for details.
WITHOUT VSP's:
Measurement 1 - Five separate strikes; LED image stabilized with circle 4, after 3 seconds had elapsed.
Measurement 2 - Five further strikes; LED image came to rest after 6 seconds had elapsed.
WITH VSP's FITTED:
Measurement 1 - Five separate strikes; LED image decayed to inside circle 4, after less than 1 second had elapsed.
Measurement 2 - Five further strikes; LED image came to rest within 1 second, i.e. the LED returned to its stationery position in one second, without oscillating within circle 4 as previously.
RESULTS:
Based on 20 individual strikes, and within experimental error, the VSP's had no discernible effect on the amplitude of the displacement. However, the VSP's significantly reduced the dampening times. Timing measurements relied on hand/eye co-ordination to start/stop the timer.
EQUIPMENT:
Vixen GP-DX GEM.
Vixen ED102S f9 refractor.
100mm focuser extension tube.
Vixen GA-3 illuminated guider (built-in 3x Barlow, 6 concentric circles)
Vixen 10mm Plossl.
3.9kg dec shaft weight.
Orion Optics (UK) pier with adjustable feet. 1.1m long.
Feet are terminated with metal plates that are slightly smaller than the VSP central pad.
OTA/MOUNT CONFIGURATION:
Dec shaft was horizontal.
OTA was horizontal.
TESTING SURFACE:
Concrete floor.
LIGHT SOURCE:
Red LED approx 25 metres away.
MECHANICAL STRIKER:
Lawn tennis ball suspended on a piece of string 30 inches long. The ball was pushed back with my extended arm, to a marker, and then let go to strike the focuser tube with a single hit to produce a reasonably consistent and repeatable striking force.
TIMER:
A kitchen LCD timer with press to stop/start button.
METHOD:
The red LED was acquired in the GA-3 illuminated guider with 10mm Plossl eyepiece. The reticule has 6 concentric circles. The largest circle (6) was visible just inside the edge of the field of view. When the focuser was struck by the tennis ball, the initial LED displacement was out to circle 5.
The first measurement was taken when the LED's amplitude was wholly within circle 4.
The second (stationary) measurement was taken when the LED ceased all movement.
Cheers
Dennis Simmons
(Just love debunking myths!)
