I'm looking at a 70-300mm sigma for the Nikon AF-D and on the specIfication it's said Filter Thread rear:58mm. What does that mean. And will a 58mm wide angle add on lens fit it? Here's the link for the Sigma and Add on lens. Thanks!
http://www.bhphotovideo.com/c/product/549304-REG/Sigma_5A8306_70_300mm_f_4_5_6_APO_DG.html
http://www.ebay.com/itm/0-45x-Soft-fisheye-wide-angle-lens-58mm-for-Canon-T3i-T3-600D-550D-18-55mm-/350605899678?pt=Camera_Lenses&hash=item51a1bd779e
>>> What does it mean by Rear:58mm?