Easiest way to go with 'third party lenses' is by an M42 screw/Sigma adaptor or via Tamron Adaptall/M42/Sigma adaptors. These will give manual lens
Snap from Tamron Adaptall 2, 35-80 mm f2.8-3.8 SP. Cost £30.00.
Generally works well and opens up a shed load of lens possibilities for very low outlay.
Best of luck.