Markers Only At One Zoom Level

Hiding markers outside of a specific zoom level
<!DOCTYPE html>
<html>
<head>
<meta charset=utf-8 />
<title>Markers Only At One Zoom Level</title>
  <meta name='viewport' content='width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no' />
  <script src='//api.tiles.mapbox.com/mapbox.js/v1.4.0/mapbox.js'></script>
  <link href='//api.tiles.mapbox.com/mapbox.js/v1.4.0/mapbox.css' rel='stylesheet' />
  <!--[if lte IE 8]>
    <link href='//api.tiles.mapbox.com/mapbox.js/v1.4.0/mapbox.ie.css' rel='stylesheet'>
  <![endif]-->
  <style>
    body { margin:0; padding:0; }
    #map { position:absolute; top:0; bottom:0; width:100%; }
  </style>
</head>
<body>
<div id='map'></div>
<script type='text/javascript'>
var map = L.mapbox.map('map', 'examples.map-zr0njcqy');

map.setView([38.90, -77], 13);

// the function given to this callback will be called every time the map
// completes a zoom animation.
map.on('zoomend', function() {
    // here's where you decided what zoom levels the layer should and should
    // not be available for: use javascript comparisons like < and > if
    // you want something other than just one zoom level, like
    // (map.getZoom > 10)
    if (map.getZoom() === 13) {
        // setFilter is available on L.mapbox.markerLayers only. Here
        // we're hiding and showing the default marker layer that's attached
        // to the map - change the reference if you want to hide or show a
        // different markerLayer.
        // If you want to hide or show a different kind of layer, you can use
        // similar methods like .setOpacity(0) and .setOpacity(1)
        // to hide or show it.
        map.markerLayer.setFilter(function() { return true; });
    } else {
        map.markerLayer.setFilter(function() { return false; });
    }
});
</script>
The code and documentation to mapbox.js is hosted on GitHub where you can contribute changes and improvements.