I am confused about the exact purpose attachment.php ( and image.php) . I notice many themes dont have them. If single.php displays the image the way I want then is it OK to leave it out. On the other hand could i just make a copy of single.php for attachment.php and leave out the sidebar.
The other thing that confuses me is that when I add a gallery to a post I get the option to open images in an attachment page but when I add a single image to a post it only gives me the option to open the image as an image file (outside of the theme - ie without menus etc). I cant understand the point of this. What is the point in having an attachment.php file for images (or an image.php file) if it isn't going to get invoked when someone clicks on an image.
Ideally what i need is a good tutorial on attachments but I cant find any and i can find very little info in the codex.