getting images from ACF relationship Field

Hi,

i use the the Advanced Custom Field Plugin, and want to show articles using the
Field Type “Relation”.
Like shown here:
http://www.advancedcustomfields.com/resources/field-types/relationship/
(Basic loop (without setup_postdata),
and it worked fine in other Projects.

Now with Timber i have Problems getting the Featured Image of a blog Post. (and the Permalink as well). All the other Stuff like Title, Excerpt, Date works fine.

here is my Code:

{% set relations = post.get_field('my-custom-fieldname') %}
     {% for relation in relations %}
	<div class="span7">
	     <article class="focus">

		<a href="{{relation.post_link}}" >
		<h2>{{relation.post_title}}</h2>
		<p class="intro">{{relation.post_content|excerpt(30)}}...</p>

		<img src="{{relation.post_thumbnail.src}}" alt="" />

		 <p>{{relation.post_date|date('j.d.Y')}}</p>
		 <p>Article by {{relation.author_name}}</p>
		 </a>

		</article>
     </div>
{% endfor %}

i tried everything i could find regarding images in timber, but without no luck.
thanks for feedback.
riikk

https://wordpress.org/plugins/timber-library/