Image enlargement caption vs filename

Hi,
I keep finding new ways to enjoy this theme. Thank you.

I also find things I don’t understand. For example: I’m using links to media two different ways so that there is an image enlargement when clicking on a thumbnail. One way is in a gallery situation such as this:
http://olufnielsen.dreamhosters.com/portfolio/abstract-textural-paintings/

And the other way is from a portfolio item such as this.
http://olufnielsen.dreamhosters.com/portfolio/moving-up/

What’s happening is that in the first case, the caption for the enlargement is from the “caption” field in the media library. In the second instance, it is grabbing the “filename” for the caption of the enlargement. I need these to be from the caption info that goes with the image. Any suggestions for doing this without having to go through the hundreds of images to change the file name?

Thank you!