I've previously owned Canon's 85mm f1.2 mkII but sold it on due to frustrations with its minimum focussing distance, and it not suiting my wanting to take head and shoulder portraits.
I have a project coming up soon which I think the 85 would ideally be suited, but I will still need to get closer that the lens allows, and so I have been considering extension tubes.
By my calculations, if a 25mm extension tube was used the 85's minimum focussing distance would be reduced from 0.95m to approx 0.3 - is this correct?
Also, how will image quality be affected?
Finally, is there a specific extension tube people would recommend for portraiture work?