A Gitzo is not really so expensive when you've been using it for over 30 years, just a few dollars for each year. My only problem with it now is I'm getting too old to carry it very easily. But the model I have I used to support an 8x10 field camera and never had a problem even with some very long exposures, which an 8x10 often requires stopped down to f/32 or even f/45.

EFX,

Thanks for your comment. The fact that I cannot go under 1/60 s at 300 mm (with DX format) is the main problem. I've used long exposure with lenses below 50 mm with success. I've visited my local photoshop yesterday (again) and they say again that a tripod cannot give more than 2 stops... It's hard to beleive. I'd rather go to with a vibration control lens instead of lugging a cumbersome tripod if this is the case! I still think that a better equipment might do the job. The question is: which and what would be the gain (f stops)?

One of the factors to consider with very long lenses using a tripod is that if the camera alone is the connection base, the weight of the lens is cantilevered well beyond the point of connection and this permits more movement and vibration than if the whole, both camera and lens was supported closer to its weight center of gravity. Some long lenses have collars available for mounting, and should be used - or there are cradles which will accomplish the same thing mounting both camera body and lens close to the weight center of both. This steadies the system considerably and can eliminate most of the usual vibration affecting image sharpness shooting with very long lenses.

It's even annoying just to compose a picture: as soon as I let go the hand that was holding the lens while composing after blocking the head, the perceptive flow lens tilt down a bit... I'm considering upgrading to a Gitzo GT3540L with a Kirk or Really right stuff ball head. But the prize is kind of scary