A rather late follow up. One

Home Forums Meteors Liquid crystal shutters for meteor observing. A rather late follow up. One

Bill Ward

A rather late follow up. One of the issues that originally confused me was the duration of the meteor from video compared to the duration determined by the chops in my still. After some tests with my system and an oscilloscope there is an effective doubling of the chops due to the way the crystals in the shutter work.

In this case the function generator was producing a square wave at 20Hz (20 times per sec) HOWEVER the crystals seem to switch with every reversal of voltage so a 20Hz rate from the function generator gives 40 chops per second. What this boils down to is that the meteor was only half as long as I originally thought but now it fits much better ;-))

Further digging around reveals that driving them this way, with a pos-neg-pos-neg voltage etc signal a: makes them work properly and b: if you use, say, zero-pos-zero etc it can cause the crystal to degrade much quicker (according to the manufacturer’s bumff.)

So, beware if you use these LC shutters, they might not give you what you think they should be giving you…!

I am now confident it was the same meteor.