Re: confused about contrast ratios


"The Simpsons" <fred.simpson@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in
message news:13no052q8mp83ec@xxxxxxxxxxxxxxxxxxxxx

"Peter Lynch" <pete@xxxxxxxxxxx> wrote in message
news:slrnfnnucc.s3u.pete@xxxxxxxxxxxxxx
I've been considering getting a new TV with a bigger screen. Given the
difficulty of sourcing a large CRT, or of having the furniture to
support it, the new set would be LCD or plasma.

Now, when I read reviews of either LCDs or plasmas, the specs all seem
to make a big deal of the "contrast ratio" of the screen, with values
in the thousands being possible.
My assumption is that this is the difference between the absolute
brightest,
eyeball-burning, most intense light they can squeeze out of a display in
the millisecond before it explodes and the light the screen gives off
when it's "black".

In an effort to get an idea of the C/R I was getting from my old TV,
I used my DSLR in AE mode. When pointed at the TV screen with the set
turned off (so all I was getting was ambient light from the room
reflected
off the screen) the camera told me I needed a 1/3 second exposure. Doing
the same measurement with a bright white image on screen, I got a meter
reading of 1/250. So my "contrast ratio" in real-life is about 80:1 and I
find this quite acceptable.

So, on the basis that my little experiment is valid (please speak up if
you can see any obvious mistakes), is there any reason why I should pay
more for one screen with a higher C/R over a similar one with a lower
value
given that they would both be 10's or 100's of times more than I would
ever
see in real life?


Well a CRT screen is refreshed once every 1/25 second so any exposure
faster than this would in my opinion give a false value.

Dear oh dear. Even 1950's sets were refreshed interlaced at 1/50s

Recent modern CRT's refreshed the whole picture [from memory] at 100Hz,
changing bits that had been updated.

With LCD's there is less of an issue with persistence, since to a first
approximation a pixel will show what it was last told to until it is told to
do something different.

Why not read users reviews at http://www.avforums.com/forums/index.php
then combine this with looking at what's on display in the stores.
Fred


.

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