I like the framegrab. The contrast is great but maybe it's a little too hot for my taste. It's all subjective though and dependant on the context.

For this particular frame, I would not worry too much about CA. And if it does worry you, just stop down the lens. A stop or more should be enough to get rid of CA and make the DOF manageable as well!

im guessing if there is (and there isnt) any CA in that image, it wouldnt be from the slr lens though. More likely from the achromat. I supposes reducing the CA from the achromat, if there were any, could be done by moving the camera further from the GG and zooming more to use more of the center of the achromat.

Thanks for the recommendations, everyone. If I understand correctly, you can't stop down a Canon FD prime when it's attached to the Letus. So it looks like a Nikon lens is the answer? I found this thread which explains how to switch from the Canon to the Nikon mount on the Letus:

http://dvinfo.net/conf/showthread.php?t=87885

Looks a little dodgy...

naw, just stick a little thing in the back of the lens to keep the iris lock bar in place. or if you have the older metal lenses the iris lock can just get locked into place to give you control of iris