I spend some time now exploring Zenphoto and do really like it.
Although I still have some difficulties understanding filters and plugins....

Can anybody please give me directions how to write a plugin/filter to add more Album Fields like AlbumLocation or AlbumCustomData. For example AlbumArtist and AlbumExhibition.
I saw that the filter-custom_data - filter but don't know how to add new fields.

sbillard gave an advice to me that was a little too vague for me: You should probably be familiar with the Zenphoto themeing tutorial and object model at this point.
Then take a look at the create_album plugin ( http://www.zenphoto.org/news/create_album ) for an example.
Looking at the create_album plugin didn't get me further.

Thank you

Well, you need to know how Zenphoto works before you can extend it. And the object model is absolutly necessary for that. We have a tutorial for that that you should have read. Reading the theming tutorial also does not hurt for the basics. There is also a lengthly article about the plugin system. All to be found on the user guide naturally.

Here is an example plugin for extending the custom fields:
http://www.zenphoto.org/news/filter-custom_data
It's actually dividing the existing custom data field and does not add further. If you need further you can of course add them to the db but better is to use the plugin_storage table. And again you need to know the object model to connect those entries with an actual item. Especially if you want to use them via meta data embeded in your images (if I recall right).

Do you use all fields like "location" at all? I mean you don't need to use the location field for a location...