[Alex KL-1]

You can use the lens effect and reduces Vg1, but you can need to compensate raising the Vg2 (screens), and also needs more video amplitude, if you wanto to maintain same contrast ratio. Perhaps a little loss of contrast can be compensated for taste sake with the sharper picture.

For me, for example, my delta-gun TV, I swears that it have more bright when it are critically focused. I not measured it, but I have a DMM with luximeter that I already measured some TV brightness, including that. Someday I measure it.

But I assume that being a side product (impression caused) of the focusing.