The fz4/5 adapter needs help. 1) Plastic threads have a short life span. 2) They are recessed 1-2mm into the front of the adapter hendering a secure connection with most threaded add-ons. 3) The adapter is too long and places converters - particularly wide angle - futher from the camera lens than is advisable. There is a rather envolved and intrusive modification at http://www.ishots.net/fz5/modified_fz5_adapter.htm that gets add-on very close to the fz5 lens but in the process removes the lens hood channels and intereferes with the locking mechanism.
Here is another, less stressful solution that replaces the 55mm plastic threads with 52mm metal threads 2mm closer to the extended lens than the stock adapter. (The above rt5264p modification shortens the adapter by another 2mm.) Take a 52mm filter (uv or otherwise ~$5 on ebay) and remove/break the glass. There is an interior ring/rib that is part of the body of the filter casing and seperates the 52mm male threads from the 52mm female threads. That ring may interfere with lens extension. If the 52mm filter w/ glass removed does not slide freely over the front portion of the extended lens, file away some of that aluminum rib with a curved metal file (~$5 at home depot, etc). You won't have to remove much if any. Slide the filter into the fz5 adapter. You'll notice that the front of the filter is about 2mm deep into the adapter. That 2mm of plastic needs to be removed. This will not effect the connection of the lens hood with the adapter. Take a sheet of fine grit sandpaper (#100) and place it on a hard flat horizontal surface and rub the front of the plastic fz5 adapter against it until the front of the inserted filter and the front of the adapter are flush. The filter can be secured with silicone sealant or by wrapping a strip of electrical tape around the outside of the filter casing to increase its outside diameter so that a tight pressure fit is accomplished. I used two thicknesses of tape and it's real tight. I took off a little bit of extra plastic and tape with a wallpaper knife after the filter was in there securely.
FZ5 adapter modified with a 52mm metal uv filter casing inserthttp://www.ishots.net/fz5adapter6600/medium/0001.jpg
Comparison with a Raynox rt5264p modified adapter on the left
http://www.ishots.net/fz5adapter6600/medium/0000.jpg
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Fred
FZ5 & FZ1v2
http://www.ishots.net