Is There An Optical Device That Lets You Preview Different Lenses Without A Camera?

I don't know too.

That 's why I'm used to do simulations with 3D softwares. In most cases It's rarely 100% perfect but you will know what focal to choose and what FOV size you will get approximatively with even better .. pixel density to avoid big mistakes, and that using background google earth maps or cad.

Second good points: you build a professional situation map with all your camera and settings for future deployments and maintenance .. Mandatory for Identification and Recognition situations (most important..)

Have a look: Computar View Finder

Back in ye olden dayes, before varifocal lenses were cheap enough to be practical, we used a viewfinder formatted for surveillance lens sizes, so you knew which lens you would need before getting on a ladder (this is when we used portable TVs as test monitors, and climbing up a ladder with one of those was a pain). I have a pretty nice one from Pentax, and of course Alex K already mentioned the Computar. I've never seen one that goes lower than 4mm, because lenses wider than that were incredibly rare back then, and besides, the resolution of cameras was so low, no one would use a super wide anyway. If you wanted to cover a large area, you might install a second camera, or, more likely, you'd put a scanner (a motorized camera mount that slowly swept back and forth) instead.

That's right. Cameras, and camera installation, was so expensive, it was cheaper to get a motorized head than to install a second camera. Of course, Murphy ensured that the camera was always pointing in the wrong direction when something that would have justified installing CCTV in the first place.

I hate Murphy so much.

Apparently they got them for 35 mm lenses, now I just need an adapter, or as Alex will point out an Avigilon PRO lens will "do It right Out of box"