Vishy Moghan on "Making the featured image link to original jpeg file"

Hi all

On my newly revamped photo folio site I decided to use Gridly. I really like the look of the front page and it suits the way I want to present my photography (http://f5.fluxink.com). I have made several mods to the template to customise it for my purposes. But there is one thing I can not work out. I have a Fancybox plugin which is great, I would like to change the featured image thumbnail link from taking me to the post into a link that would open the image in full size in the fancybox. But also leave the title to guide the user to the post page if they choose.
Now I tried changing the class in the a href of the index php successfully to fancybox, but this popped the whole post in a pop up.

Can anyone tell me what to write and where to make the featured image pop up when clicked showing the original size image file?

This was the simple mod I did that worked to an extent as mentioned above:

<div id="post-<?php the_ID(); ?>" <?php post_class(); ?>>
		 <?php if ( has_post_thumbnail() ) { ?>
         <div class="gridly-image"><a>"><?php the_post_thumbnail ( 'summary-image' );  ?></a></div>

		  <?php } ?>
       			<div class="gridly-copy"><h2><a>"><?php the_title(); ?></a></h2>

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Thanks