Slider that goes from 0 to 50 to half and after half from 50 to 1000

Not exactly like the Gaussian Blur, but close to what you ordered.

The center and end values can be changed as desired.

var m1 = 50;   // center value
var m2 = 1000; // max value
var exp = Math.log(m2/m1)/Math.log(2); 


var dialog = new Window("dialog");
dialog.text = "EXAMPLE";
dialog.orientation = "column";
dialog.alignChildren = ["left","top"];
dialog.spacing = 10;
dialog.margins = 10;


var panel1 = dialog.add("panel", undefined, undefined, {name: "panel1"});
panel1.text = "EXAMPLE";
panel1.orientation = "column";
panel1.alignChildren = ["fill","top"];
panel1.spacing = 0;
panel1.margins = 0;

var panel2 = panel1.add("panel", undefined, undefined, {name: "panel2", borderStyle: "one"});
panel2.orientation = "row";
panel2.alignChildren = ["left","top"];
panel2.spacing = 10;
panel2.margins = 10;

var slider = panel2.add("slider", undefined, undefined, undefined, undefined, {name: "slider"});
slider.minvalue = 0;
slider.maxvalue = Math.pow(m2, 1/exp);
slider.value = 0;
slider.preferredSize.width = 268;

var edittext1 = panel2.add('edittext {properties: {name: "edittext1"}}');
edittext1.text = slider.value;
edittext1.preferredSize.width = 50;

slider.onChanging = function () {

var x = Math.pow(slider.value, exp);

if (x > 10) x = Math.round(x);
else if (x > 1) x = Math.round(10*x)/10;
else if (x > 0.1) x = Math.round(100*x)/100;
else  x = Math.round(1000*x)/1000;

edittext1.text = x;
}

var statictext1 = panel2.add("statictext", undefined, undefined, {name: "statictext1"});
statictext1.text = " px";

dialog.show();

P.S. I'm not sure if the values in the other points of the slider will suit you. : )