Problems using macro lens

Hello everyone,

I tested my new macro lens (in my living-room...) this week-end, and I quite worried about the quality on the shots using the DS 125.

Combo : Canon G2 in Ikelite Housing and single DS 125 in TTL

In order to get rid of vignetting, I used the longest focal length (21mm). But while the upper left parts of the shots (on the strobe side) are usually well lit by the strobe, the lower right parts are in the shade... I tried to put the strobe in different positions, closer to the subject, forward, backward... nothing changed. Where does this shade come from?

Here are my question :

1. What's the best strobe postion to take a macro shot ?

2. What can I do to insure an homogeneous lighting, and prevent these shaded colors?

Thanks a lot

Test the lens in water. The results in air are probably not indicative of the actual results.

Also, it would help if you attached a sample photo.