echo multiple custom fields

Maybe this is simple but I can’t find the answer – I’ve got multiple custom fields called photo1, photo2, photo3 etc., and I’m trying to print them all in single.php but the code I am using only prints 1 – can anyone help? (php newbie) I thought $single = false would work but it doesn’t seem to.

<?php
if(get_post_meta($post->ID, "photo1", $single = true) != "") :
?>

<img src="<?php echo get_post_meta($post->ID, "photo1", $single = true); ?>" alt="<?php the_title(); ?>" />

<?php
endif;
?>