Question on CouchDB View

In my CouchDB application, blog/photo is identified by the type field in the document.

{
    "type": "blog",
    "title": "First Blog",
    "when_created": "01/20/2011 15:30:00",
    ...
}

{
    "type": "photo",
    "title": "First Photo",
    "when_created": "01/21/2011 15:30:00",
    ...
}

To get the latest content, I created a view with map function as below.

// View name: latest
function (doc){
    if (doc.type == "blog" || doc.type == "photo") {
        emit(doc.when_created, null);
    }
}

Now I can sort the view by when_created field.

Similarly I created two other views for latest blogs and latest photos as below.

// View name: latestblogs
function (doc){
    if (doc.type == "blog") {
        emit(doc.when_created, null);
    }
}

// View name: latestphotos
function (doc){
    if (doc.type == "photo") {
        emit(doc.when_created, null);
    }
}

But the view "latest" will have duplicate data, It contains the data which is already available in "latestblogs" and "latestphotos" views.

So I planned to create a single view function with complex key as below.

// View name: latest2
function (doc){
    if (doc.type == "blog" || doc.type == "photo") {
        emit([doc.type, doc.when_created], null);
    }
}

Now I can get list of new blogs/photos by adding startkey and endkey to the view as below

// List of new blogs:
startkey=["blog", {}] endkey=["blog"] descending=true

// List of new blogs:
startkey=["photo", {}] endkey=["photo"] descending=true

To get all the records irrespective of type, call the view without startkey and endkey parameters. But the issue is all are sorted by first element of key not by when_created.

How can I get latest 10 elements irrespective of doc.type. (sorted based on second element of key)