JVC TK-S340 lens; how do I change it??

Hi all ;- )

I´m a complete newbie to cctv, and I need to be able to monitor a cnc milling machine from a distance (50 feet) where I have my PC, away from the workshop area, while the machine mills a piece in stone, which can take hours. So I just got a JVCTK S-340, analogue camera second-hand, at 15€. It came with 2 lenses.

I also have an old B&W tv monitor, which works ok. When connected, the image quality is acceptable.

I´d like to be able to change lenses to see if image quality improves: there is a “BF” lock adjustment screw on one side, and there is a knurled wheel which sticks out of the case slightly, which gets freed once you unscrew the screw; what´s its use? I thought it might be lens release, but the lens only revolves about 200º, and stops, without coming off the camera. I don’t want to force it.

The second lens has fine threads on it.

Also; I assume the “video iris” is the shutter?

The “video iris” connections on the back; Ground, Video and +9vdc; there is a 9vdc tension on that pin; what´s all that for?

I assume the L H Level adjustment on the side is for ......light level of the scene?

I can imagine what Sync In is, but how do you connect it and where/why?

“Phase”; there are 3 DIP switches, (BLC (Back Light Compensation) , AES (Auto Electronic Shutter) , and Int/Ext LL Sycn) and an adjuster; the first 2 are self explanatory, but whats the importance of the Int/Ext LL Sync; ?

So any information would be greatly appreciated.

I tried to upload some shots, "too big" will try again.

Regards!

Frank