is there a way to find out specs of lenses just by inspecting visually?

[foretpaulgmj]

I recently acquired some CCTV lenses like the one in the picture. there is no writing on it, I was wondering if there is a way to figure out the specs by inspecting visually.
thank you

 

[VorlonFrog]

Check to see if the mm rating is hot-stamped into the ring around the lens somewhere

 

[bp2008]

Maybe with specialized equipment you could tell, but I wouldn't even know what to suggest.

Chances are the quality of random unmarked lenses isn't very good anyway, so even if they turn out to be compatible with a modern IP cam, they might not focus very well and might not be IR-corrected. Also some lenses have permanent IR filters built in.

 

[pozzello]

If you have other lenses of known specs, ie, one that's known to be 4mm, etc, you can compare by shining a laser-pointer type light thru it from the back end and see how far it disperses (at a fixed distance from the projection surface, of course). So, holding the lens 6" above a sheet of paper or other surface, the 4mm lens will throw a narrower image than a 2.8, for example...