Just solved it myself! Here’s the answer (might conceivably be of use to someone else):
<!-- slideshow -->
<?php if( have_rows('news_slideshow') ): ?>
<!-- data-ratio="820/542" -->
<div class="the-slideshow slideshow-news">
<div class="fotorama"
data-width="100%"
data-ratio="820/542"
data-minwidth="285"
data-loop="true"
data-swipe="true"
data-click="true"
data-nav="false"
data-transition="crossfade"
data-transitionduration="1500"
data-autoplay="4000">
<?php while ( have_rows('news_slideshow') ) : the_row(); ?>
<?php if( !empty(get_sub_field('news_slideshow_image')) ) : ?>
<?php
$slideLarge = get_sub_field('news_slideshow_image');
$size = 'full'; // (thumbnail, medium, large, full or custom size)
?>
<?php echo wp_get_attachment_image( $slideLarge, $size ); ?>
<?php else: ?>
<?php echo 'something else'; ?>
<?php endif; ?>
<?php endwhile; ?>
</div>
</div>
<?php endif; ?>
<!-- end slideshow -->
