ti lenjo lo gusni lo darno
This lens focusing light has a long focal length.
Correct?
Now what about lenjo2?
lenjo = x1 is a lens/glass [focussing shape/form] focussing x2 to focus/foci x3 by means/material x4. (adjective:) x1 is optical; focussing may be optical or otherwise, hence x2 which may be light, sound, X-ray, etc., default is light/optical lens; ka is refraction. See also kacma, minra.
Can it be other than {LE gusni}?