ttl (through the lenses) loupes TTL style: rhe loupes Through The Lens are light weight, and laconic appearance. It has fashionable design and comparable with designer frames 250s/TTL with very small and light weight lens, providing wide field of view Items: 250sR/TTL, 250sL/TTL Power: 2.5X Working distance: 340mm(S),500mm(L), Depth of view: 90mm (S); 110mm (L); Field of view: 90mm (R); 100mm (L) Interpupillary distance: 59-61mm; 61-63mm;63-65mm Weight: 58.5g Frames: Ni-alloy or Titanium 2.5X normal TTL loupes Items: 250S/TTL, 250R/TTL, 250L/TTL, 250XL/TTLL Power: 2.5X Working distance: 340mm(S), 420mm(R), 500mm(L), 550mm(XL, Depth of view: 80mm (S); 90mm (R); 110mm (L); 120mm(XL) Field of view: 90mm (S); 100mm (R); 110mm (L); 120mm(XL) Interpupillary distance: 59-61mm; 61-63mm;63-65mm Weight: 60g Frames: Ni-alloy or Titanium 3X TTL loupes Items: 300S/TTL, 300R/TTL, 300L/TTL, 300XL/TTL Power: 3.0X Working distance: 340mm(S), 420mm(R), 500mm(L), 550mm(XL, Depth of view: 50mm (S); 60mm (R); 80mm (L); 90mm(XL) Field of view: 60mm (S); 70mm (R); 80mm (L); 90mm(XL) Interpupillary distance: 59-61mm; 61-63mm;63-65mm Weight: 69.5g Frames: Ni-alloy or Titanium 3.5X TTL loupes Items: 350S/TTL, 350R/TTL, 350L/TTL, 350XL/TTL Power: 3.5X Working distance: 340mm(S), 420mm(R), 500mm(L), 550mm(XL, Depth of view: 50mm (S); 55mm (R); 60mm (L); 65mm(XL) Field of view: 50mm (S); 55mm (R); 65mm (L); 70mm(XL) Interpupillary distance: 59-61mm; 61-63mm;63-65mm Weight: 73g Frames: Ni-alloy or Titanium