Breakdown of Мы фокусируем луч на экране посредством этой линзы.
мы
we
этот
this [f: эта, n: это]
на
on, at / by (transport) / to (a place) / to (in answer to)
экран
screen
луч
beam
посредством
by means of
линза
the lens
фокусировать
to focus (optics, camera, attention)
Questions & Answers about Мы фокусируем луч на экране посредством этой линзы.
Why use the formal preposition посредством here instead of just putting 'this lens' in the instrumental case?
посредством (meaning 'by means of') takes the Genitive case (этой линзы). While you could just use the bare instrumental case (этой линзой) to show the instrument used, посредством is highly formal and precise. It fits perfectly in scientific or technical contexts like optics.
Could we swap посредством with the other compound prepositions from this lesson, с помощью or при помощи?
Absolutely. с помощью этой линзы and при помощи этой линзы both mean exactly the same thing and also take the Genitive case. посредством is simply the most formal and academic option among them.
Why doesn't the word луч (ray) change its ending, since it is the direct object of the verb?
It actually is in the Accusative case here! Because луч is a masculine inanimate noun, its Accusative form looks exactly like its Nominative (dictionary) form.
What is the infinitive of фокусируем and why does it have that -у- in the middle?
The infinitive is фокусировать (to focus), which is an imperfective verb based on a foreign loanword. Like most Russian verbs ending in -овать, it drops the -ова- and replaces it with -у- or -ю- when conjugated in the present tense (for example, я фокусирую, мы фокусируем).
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