Ordinarily, with the F250 camera, you'd need a CCU to remotely control the iris, but you can build your own basic remote control unit. Pin 32 on the 32-pin camera connector, connects directly to the iris control circuitry, and all you need is a few basic components. Other camera controls use a time-multiplexed serial data system, which is a lot harder to home brew. Though adding a working tally input isn't difficult.
When the auto/manual switch on the camera lens is set to auto, the lens can be remotely controlled by the voltage on pin 32. Grounding the pin sets it into auto-iris mode. Raising the voltage to about 2 volts, closes the iris. Raising the voltage to about 9 volts, opens it. And varying it between those points gives you direct manual control. It is real manual iris control, rather than offsetting the auto-iris by a variable amount, providing that your lens is one of the types with a potentiometer in it. If your viewfinder gives you F-stop readings in the on-screen-display, as you manually control the lens, you have a lens with a potentiometer in it (it senses the position of the iris ring).
For an easier to use iris control: Connect a 6.6kΩ resistor between a 12 volt power supply an the clockwise pin of a 10kΩ pot, and a 3.3kΩ resistor between the anti-clockwise pin and ground. And connect a switch between ground and the pot wiper, leading to the iris control pin. This gives you a pot which uses the full rotational range of the pot for manual iris control (from fully-closed to fully-open), and a switch to change between auto and manual iris control.
The 12 volt supply needs to have a common ground with the camera.
As a slight improvement, you could replace the resistors with trimpots, so you could tweak the range of the pot, precisely. Perhaps you want the pot to go from F22 to open, but not completely close shut. Or, use full-sized pots, to allow custom preset open and close limits to the main iris control, giving you fine control between a small range of iris positions.