Problems with The Columnist and custom fields

I am trying to switch my theme over to The Columnist (http://thecolumnist.info/ and http://theme.wordpress.com/themes/the-columnist/) and I am unable to get the images to show up as instructed. The documentation says to place the URL of the image you want in a post in the custom fields. However, when I do that, nothing shows up.

For example, the documentation says “You can define which image you would like to use by entering the URL in the custom field titled: ‘Large Image (625×390)’.” So, I put ‘Large Image (625×390)’ in the custom field and then the full URL of the image I want as the value, and nothing shows up. (I’ve put ‘Large Image (625×390)’ in the name with and without the apostrophe.)

It doesn’t look like the theme’s author is participating in any support. I was wondering if anyone had a similar problem or can provide any suggestions.