Hi @wickywills
The get_field_object function only works with parent fields. To find a sub field object, please use the get_sub_field_object function.
This function is documented below and was added in v4:
http://www.advancedcustomfields.com/resources/functions/get_sub_field_object/
Perhaps for now, you could use a work around like so:
<?php
$field = get_field_object('repeater_field_name');
$sub_fields = $field['sub_fields'];
// debug variable to find the sub field key ($key)
echo '<pre>';
print_r($sub_fields);
echo '</pre>';
die;
$sub_field = $sub_fields[ $key ];
?>
