Thank you @jaomul & @bratkinson for saving my other gear's life. The infected lens is now good after a service which costs about $100. such a great punishment for not taking care of my equipment. Not only the rear and 2nd rear glass but a glass in the middle was also replaced. the lens can now...
Is it possible to get the same depth of field with different lens? Let say If I want to get as shallow DOF as a 50mm can do at f1.8, but I only have a 24-105mm f4, so I zoom in to 105mm @ f4, will the DOF be the same like the 50mm @ f1.8? There might be a perspective compression difference but...