Why etree.find doesn't find the element for the provided example

Lets suppose it has this:

xml_as_str = '''
<v1:Header>
    <v2:Person>Foo Bar</v2:Person>
    <v2:Email>foo@bar.com</v2:Email>
</v1:Header>
'''

from lxml import etree
tree = etree.fromstring(xml_as_str, etree.XMLParser(recover=True))

How could it get the value of certain tag, e.g "Foo Bar" for v2:Person ?

I've tried this:

 >> tree.find('.//v2:Person')
 >> tree.find('.//{Person}v2')

in order to get the element and then .text, but .find doesn't find the element, why?.