Ultrasphinx help

I switch from ferret to ultrasphinx.

In my table user I have following fields

id, firstname, lastname, login, password, created_at, updated_at

is_indexed :fields => [{:field => :login},{:field => :firstname},{:field
=> :lastname}]

Now what I want is to search with a character
like if you write 'm' then search m in login field where ever it find

In ferret it works.