diff --git a/js/geometric-optics-basics-main.ts b/js/geometric-optics-basics-main.ts
index 0335f7a..d0c0f15 100644
--- a/js/geometric-optics-basics-main.ts
+++ b/js/geometric-optics-basics-main.ts
@@ -6,44 +6,26 @@
  * @author Chris Malley (PixelZoom, Inc.)
  */
 
-import GOConstants from '../../geometric-optics/js/common/GOConstants.js';
 import GOGlobalOptions from '../../geometric-optics/js/common/GOGlobalOptions.js';
 import GOQueryParameters from '../../geometric-optics/js/common/GOQueryParameters.js';
-import LensScreen from '../../geometric-optics/js/lens/LensScreen.js';
-import MirrorScreen from '../../geometric-optics/js/mirror/MirrorScreen.js';
-import Sim from '../../joist/js/Sim.js';
+import GOSim from '../../geometric-optics/js/GOSim.js';
 import simLauncher from '../../joist/js/simLauncher.js';
-import Tandem from '../../tandem/js/Tandem.js';
 import geometricOpticsBasicsStrings from './geometricOpticsBasicsStrings.js';
 
 // If enable2F query parameter was not in the URL, change the default.
+// This must be done in geometric-optics-basics-main.ts so that it only affects that sim.
 if ( !QueryStringMachine.containsKey( 'enable2F' ) ) {
   GOQueryParameters.enable2F = true;
 }
 
-const simOptions = {
-
-  credits: GOConstants.CREDITS,
-
-  // pdom options
-  hasKeyboardHelpContent: true
-};
-
 simLauncher.launch( () => {
 
   // ?focalLengthControl is ignored, and the 'direct' focal-length model is used.
   // This must be done inside the callback to simLauncher.launch.
   GOGlobalOptions.focalLengthControlTypeProperty.value = 'direct';
 
-  const sim = new Sim( geometricOpticsBasicsStrings[ 'geometric-optics-basics' ].title, [
-    new LensScreen( {
-      isBasicsVersion: true,
-      tandem: Tandem.ROOT.createTandem( 'lensScreen' )
-    } ),
-    new MirrorScreen( {
-      isBasicsVersion: true,
-      tandem: Tandem.ROOT.createTandem( 'mirrorScreen' )
-    } )
-  ], simOptions );
+  const sim = new GOSim( geometricOpticsBasicsStrings[ 'geometric-optics-basics' ].title, {
+    isBasicsVersion: true
+  } );
   sim.start();
 } );
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