nested partials parameters

Hi

I have presently the following view :

<div>
  <p><%= f.label :tz_area, I18n.t("label.form.tz_area") %></p/>
  <div id="tz_area_selector">
    <p>
                   <%= f.label :timezone,
I18n.t("label.form.timezone") %><br />
        <%=
f.time_zone_select :time_zone, /"#{@instructor.tz_area}"/, :default =>
@instructor.time_zone %>
    </p>
  </div>
</div>

As I need to modify the time_zone_select when another field is
modified, I'll use an Ajax request , so I am using a partial and
replaced this code with

<div>
  <p><%= f.label :tz_area, I18n.t("label.form.tz_area") %></p/>

  <div id="tz_area_selector">
              <%= render :partial => "tz_selector", :locals => { :f =>
f } %>
  </div>

</div>

the Ajax request is performed, and my controller try to replace the
partial
....
    render :update do |page|
      page.replace_html 'time_zone_selector', :partial =>
"time_zone_selector", :locals => { :f => f }
    end

but obviously I get an error ,as f is undefined :

NameError (undefined local variable or method `f'

how can I replace this piece of the form ?

thanks

erwin