OpenLayers - Control zoom level granularity?

I am not sure if this is meant to be an OpenStreetMap question or an OpenLayers question. If it is an OpenLayers question then this is the wrong place to ask; therefore I'll treat it as if you were asking for OSM specifically.

OpenStreetMap data on the OSM tile server is rendered to tiles on the fixed zoom leves that you see. You have two options:

• interpolate - i.e. take the zoom level 5 tiles and reduce them a bit, or take the zoom level 4 tiles and increase them a bit. This is what the web site http://www.khtml.org/ does, where you can select intermediate zoom levels.
• render your own map (enter "render map" in the search box above to find details) - if you do that then you can specify exactly which area and size you want and the renderer will do its best to fulfil the request.

Another noddy way of getting a map at half-zoom-level, is to tell your browser to zoom. 'View' menu. Zoom out.

This works with firefox and safari. Not sure about I.E. It amounts to the interpolation technique federik describes, which introduces unpleasant scaling artefacts. In fact because the browser is scaling quickly on-the-fly, it'll not do a particularly nice job of it. It can even result in spurious gridlines appearing (pixel gaps between tiles). In other words this is a completely half-assed solution :-)

Having said that, I've actually found this handy on a number of occasions when trying to get a quick map screenshot (usually for creating cake diagram images) Don't forget to do view -> zoom -> reset afterwards though.