Re: Apple video bandwidth question

[MdntTrain <js@cimmeri.com>]

> The reason that risetime is important for Apple monitors is that the
> appearance of a pattern with single-line horizontals and single-pixel
> verticals will have noticeably different brightness of the horizontal and
> vertical parts if the risetime of the monitor limits the amount of time
> that a pixel is at or near 100% response.

Michael, thanks for the very informative tech brief.

Yes, I observed these line brightness differences in the Sony PVM-1910
(the one you helped me fix) when connected to a IIe, even just in HGR
mode.  Horizontal lines are nice and bright (due to DC level of
signal), whereas vertical lines were somewhat dimmer.   If I plot a
second vertical line right next to the first, suddenly, they both
become as bright as the horizontal... of course now due to the longer
phosphor energizing time.

I did another experiment feeding in a pure sine wave to its RGB port
try to find out the effective resolution of the whole monitor (the
point at which I see a solid screen unchanging with frequency change)
-- screen became solid at around 4mhz.  Feeding in a square wave
resulted in a much brighter picture, but one that dropped rapidly in
brightness as I again arrived at 4mhz.

Everything you just stated explains all this phenomenon.

Thank you.
 jS