Selection of a lens for great depth of focus and short focal length

I designed my own night vision system with a DVD player screen + electronics, a 11.1 VDC lipo battery, two action camera mounting systems, a 2-7×32 riflescope, a PVC coupler (for eye relief), one CCTV camera and a lens a streamlight IR LED spotlight.

The lens is a Pentax Cosmicar C31631PL C1614ER C Mount 16mm CCTV Lens. The camera is a samsung scc-b2391 day and night digital camera.

Here is my problem. The setup works, I can display a picture successfully as planned, but I can not focus the picture clearly on the net and the target. I too have a bit of a fisheye effect. I suspect that a fixed focus and a mismatch in the format (camera 1/3 super HAD CCD lens 2/3 is) or are each to blame. Another point I may be able to contribute is my inexperience in setting up the Auto Iris, which was also a struggle for me. It works constantly now, without flickering or completely closing with changing light. My earlier setup was able to get a sharp, sharp image of both the crosshairs and the target. The problem was again that the image of the screen did not take up enough. The 16mm CCTV lens provides a nice full screen, but not sharp enough. How can I focus the crosshairs and the target? I know that someone who knows how to set up photographic equipment can tell me what to do.

UPDATE: I have now switched to a Pelco F1.6 / 5-40mm C surveillance camera lens for surveillance cameras. This has solved 90% of my problems. I am sure that I still have room for improvement so we would be happy to receive additional information.