##UPDATE! I think that this plugin is now obsolete. I haven't tested it yet but I think now you can use the zoomDelta property in native leaflet
This is a simple plugin that makes use of a new feature in the leaflet 1.0 beta, fractional zooming. You can now zoom by any increment.
demo: http://turbobuilt.com/leaflet/fractional-zoom-control/demo.html
Usage of the plugin is just like the regular leaflet fractional zoom plugin, except you need to tell it what the zoom increment should be. To use, YOU MUST BE USING LEAFLET 1.0!
First, replace your current leaflet installation with the 1.0 beta:
<script src="http://cdn.leafletjs.com/leaflet-1.0.0-b1/leaflet.js"></script>
<link rel="stylesheet" href="http://cdn.leafletjs.com/leaflet-1.0.0-b1/leaflet.css" />Then add zoomControl:false to your map. Then create the zoom control with a zoomIncrement parameter like so:
map.addControl(L.control.fractionalZoom({position: 'topright', zoomIncrement:.2}));Here is a complete demo file
<!DOCTYPE html>
<html>
<head>
<script src="http://cdn.leafletjs.com/leaflet-1.0.0-b1/leaflet.js"></script>
<script src="leaflet-fractional-zoom-control.js"></script>
<link rel="stylesheet" href="http://cdn.leafletjs.com/leaflet-1.0.0-b1/leaflet.css" />
</head>
<body>
<div id="map" style="width: 800px; height: 600px"></div>
<script>
var map = L.map('map',{
zoomControl:false
}).setView([40,-100], 12);
L.tileLayer('http://tile.osm.org/{z}/{x}/{y}.png', {
//maxZoom: 18,
attribution: 'Map data © <a href="http://openstreetmap.org">OpenStreetMap</a> contributors ' +
'<a href="http://creativecommons.org/licenses/by-sa/2.0/">CC-BY-SA</a>, ',
id: 'mapbox.streets'
}).addTo(map);
map.addControl(L.control.fractionalZoom({position: 'topright', zoomIncrement:.2}));
</script>
</body>
</html>