Dimmer Laws - Demux 48

[sp]

I've seen it a few times that the Square Dimmer Law is "for use with video cameras." What exactly is meant by this?

 

Also, for usual theatre generics, is it best to use the S or Linear Law? Looking at the curves in the Demux 48 manual, it would seem that linear is best? I can't see it in the manual - is it possible to set a dimmer law for all channels simultanously on a demux 48?

 

Thanks,

sp

[Paul]

Video cameras are more sensitive than the human eye to variations in intensity at high light levels. The square law is intended to compensate for the response curve of a video camera, so that the brightness as seen by the camera varies linearly with the control input to the Demux. I'm not sure if this is so much of an issue with modern CCD cameras as it was with old tube cameras, maybe a google around the subject will find you the answer.

 

The nature of phase control on a sine wave (how all triac dimmers work) will give you the S-Law (sometimes called Normal) curve if no correction is applied to the control input. This is quite acceptable in most situations.

 

The linear law, which should strictly be called the linearising law, applies an inverse S curve so that the output of your dimmer will respond linearly to the control input.

 

As to which law is "best", it depends on your lamps, whether it's for TV or live, what kind of effect you're trying to create etc. etc. Experiment and see which works best for you.

 

Unfortunately there is no way on a Demux48 to set the law for all channels at the same time. You can do it on the newer Demux24 though