You don't want to save weight with the tri-pod, You want a very steady tripod. I am using a 645 AFD/P45 with a Manfrotto 3021 tripod and 410 head and still feel that it is not heavy enough for that system. I do have both the Manfrotto and
Gitzo carbonfibe tripods, I really think they are too light for sharp images. They are good for indoor with strobes.
The Mamiya 300mm f/2.8 lenses is very sharp, I have one and use it for my system. I do used it on a very heavy tripod, a Gitzo 555. with a number 5 head. Keep checking on Ebay, you could get one at a very good price.
There are many reasons, why you do not get a sharp image, one of them is keeping the camera system steady enough. A good tripod is always a good way to start.
I am looking for a lightweight tripod for my ZD. Has anyone have any experience with the Manfrotto 055 series and/or the neotec. I will use my 029Manfrottto head with it. Are these smaller ripods steady enough with long exposures? Apart from the weight advantage are the carbonfibre tripods sturdier than the metal equivalents?
How sharp are the mamiya 300mm lenses. I am talking about the (older) manual focus lenses.