If at last you've found the answer, press the title to give it below.

I'm done to many things at last,

To the first bottle went down fast,

To the main lights and focus view,

To time as there's nothing to do

About it, near it, closing in

For I may be a mortal sin.

'Are you also done to cork screws? And fountain pens?'
'I'm done to many things, but not them. Though what the cork holds or the nib flows perhaps.'

Riddle Answer A Kill

Riddle Explanation
to the first bottle went down fast - to kill the bottle, or to drink it all up.

to the main lights and focus view - to kill the lights, or turn the lights off.

to time as there's nothing to do - to kill time or to have time to kill.

about it, near it, closing in for I - to close in for the kill.

for I may be a mortal sin - according to the Catechism of the Catholic Church murder is a mortal sin, though, unless avoidable or without proportionate reason, accidental killing is not.