Hi Lads&Ladies, I want to get a bit closer to my model at times but my 80mm lens can't focus for a head shot since it won't go closer than than a meter.

Now can I just screw any extension tube from Hasselblad on the camera or should I go for a certain lenght? I can't find much info on this.

And how bad is the balloon effect with and 80mm lens for portraits I hear people speak about?