Copy Composer´s renderTarget

Questions
1

I have 2 EffectComposer - both rendering same scene but with different effects. I now want to copy final effect of EffectComposer 1 (-> this.composer) over to EffectComposer 2 (-> this.blendComposer)… I fail miserable!

Is there an example I could check or see how it is done right?
I thought I “just” use renderTarget of composer1 one as “input” (-> tComp) in a shader for composer2 … but #fail

this.blendComposer = new EffectComposer( this.renderer, blendRenderTarget );
this.blendComposer.addPass( new RenderPass( this.scene, this.camera ) );

let simpleCopyShader1 = {
      uniforms: {
        tDiffuse: { value: 0 },
        tComp: { value:1 }
      },

      vertexShader: [
        'varying vec2 vUv;',

        'void main() {',
        'vUv = uv;',
        'gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);',
        '}',
      ].join('\n'),

      fragmentShader: [
        'uniform sampler2D tDiffuse;',
        'uniform sampler2D tComp;',
        'varying vec2 vUv;',

        'void main() {',

        'vec4 color = texture2D( tDiffuse, vUv );',

        'vec4 color1 = texture2D( tComp, vUv );',
        'gl_FragColor = color1;',

        '}',
      ].join('\n'),
    };

    simpleCopyShader1.uniforms["tComp"].value = this.composer.renderTarget2;

    let simpleCopyPass1 = new ShaderPass(simpleCopyShader1);
    this.blendComposer.addPass( simpleCopyPass1 );