I am trying to get a macro lens, and affordability is a real issue for me. I've been looking at & pricing used Sigma 150mm and 105mm F2.8 EX DG OS HSM lenses. Having no experience with macro lenses, I was hoping I could get some advice here as to the difference in the distances I can be from an object. How far away can I be from my object with each lens? Thank you in advance for any help.