Exponential slider query...

Hi there - 'May the fourth' be with you all...

I’m having some trouble figuring out how to get a slider to control an effects property in the precise way I want it to. I’d initially thought I could just use the linear() function, but clearly I hadn’t thought things through properly…

Describing the actual scenario would probably be unnecessarily long-winded to go into, so I’ve just come up with an analogous hypothetical situation, which should help explain more simply the basic principle that eludes me…

Let’s say that I want to link a layer's opacity value to a null's slider control and have it translate the input in the following way:

When the slider is set at zero, opacity = 50
If we turn the slider up to 1.0, opacity = (50* 1.05)
And then if we turn it up another notch to 2.0, opacity = (50* 1.05)*1.05
… And so on, multiplying the previous value by the same amount each time. It also needs to work in the opposite direction – if the slider is set to a negative value, it should divide the previous value by the same amount each time, so if the slider = -1.0, opacity = (50/ 1.05).

Thanks in advance,

DP