URL through custom field returning null

Refer ACF link : Link

And use

<?php echo get_field('aboutus_img'); ?>

Choose option image url

This example demonstrates how to display the selected image when using the Image URL return type. This return type allows us to efficiently display a basic image but prevents us from loading any extra data about the image.

<?php if( get_field('image') ): ?>
    <img src="<?php the_field('image_field_name'); ?>" />
<?php endif; ?>