Lecturing should be like theatre - not cinema.
The best way to lecture is in real time - as one person to others, in the same
room, in direct sensory contact, and with the living voice; and writing in real time on a black- or white-board; therefore not
through a microphone; not using slides nor other pre-prepared material.
Electronic amplification and imaging interpose between lecturer and class.
Can you imagine sitting talking to a friend or family member, and
that family member was talking to you through a microphone, so that you heard only their amplified voice! Imagine
how that would distance the other person from you even if they
were sitting right next to you.
Consider the difference between seeing a person on something like Skype, and in real life?
And with writing there is a difference between somebody writing you a
note - here and now, done for you - and handing you a printed leaflet which they prepared earlier.
And there is a difference between looking at that note as it is
sitting in front of you, and seeing an image of that note - enlarged on a screen, several or many yards away.
The technologies of imaging and amplification interpose
between one person and another - they just do; always they block (to some significant extent) direct, real time, here-and-now interaction.
Somehow, this even applies to electronic books or readers such as the Kindle, when compared with paper copies. It just does - even despite that in theory the electronic page looks almost like a printed page.
To some extent we can be-fooled and can fool-ourselves that electronic reproductions are 'the same' as direct perceptual contact - but only to some extent.
If we use electronic media to experience reality, it sets a cap on the reality of real life. When lecturing is an electronic experience, then there is a cap on its perceived reality.
Electronic amplification and imaging interpose between lecturer and class, therefore amplification and imaging should if possible not be used; and if amplification or imaging must be used - then it should be acknowledged that these technologies are necessarily diminishing and sub-optimal.