150 mm lens For wha is that knob?

[flashmxfreak]

I would like to know for what is that know I marked with the red rectangle.

Lens:
150mm f4 T*

Thank you

 

[jotloob]

That knob is for deth of field control .
If you push the button down , the aperture closes to the chosen value .
Now you can see the DOF for your focused distance .
If you then press the lower part of the button , the aperture returns to it open position .

 

[wbulte]

That knob is for deth of field control .
If you push the button down , the aperture closes to the chosen value .
Now you can see the DOF for your focused distance .
If you then press the lower part of the button , the aperture returns to it open position .

Time to go buy a Wildi

Wilko