Video and data projection
Why won't our iMacs work with our LCD projectors?
nothing wrong with your projectors, but unfortunately, that doesn't
mean they'll work properly with an iMac.
the iMac DV (that is, the model with an RGB output, introduced
in 1999), Apple decided to depart from the usual practice of computer
manufacturers. Most Mac and PC models use a true multisync monitor
and allow you to display multiple resolution signals at a variety
of refresh rates (i.e. 800 x 600, 1024 x 768, etc. at about 70
- 80 Hz. (Note that the refresh rate is also known as the scan
rate vertical, and that's how you'll find it specified in our
projector catalog.) Thus there is no problem sending a signal
to a large-screen monitor, LCD or DLP projector from most computers.
With the iMac,
however, Apple allowed only three display choices:
640 x 480
(VGA) resolution at 117 Hz refresh rate.
800 x 600 (SVGA) resolution at 95 Hz refresh rate.
1024 x 768 (XGA) resolution at 75 Hz refresh rate.
This caught a lot of manufacturers by surprise. Very few monitors
or projectors will sync up at 117 Hz, and the majority will not
sync at 95 Hz. (Almost any projector will sync up at 75 Hz.)
at least three solutions to the problem.
1. Go to your
iMac "Monitors" control panel and switch to 1024 x 768
at 75 Hz.
simple enough, but there's a hitch—hopefully minor. Assuming that
you, like most educators, are using native 800 x 600 projectors
and assuming your projectors can show 1024 x 768 (a few cannot),
your 1024 x 768 image will be "compressed" or "resized"
to 800 x 600. The quality of the final image will depend on the
quality of the compression or resizing algorithm built into your
projector, but it will be at least somewhat compromised.
2. Pick up a piece of shareware called "SwitchRes"
or "SwitchResX." This simple software allows the iMac
DV to output a signal at a lower refresh rate—low enough to allow
almost any monitor or projector to work. SwitchRes works well,
but there's one hitch: since the iMac's built-in monitor will
not work with the lower refresh rates, you'll essentially turn
off your built-in monitor when you "turn on" your projector
You can download the program from www.tucows.com (Search for
"SwitchRes"). You can also go the the vendor site at
www.madrau.com. If all else fails just search the web for "Switchres"
with your favorite search engine. This is a shareware program.
The cost, if you keep it is $15.00.
3. If you're planning to buy new projectors, be careful that
your new projectors will handle a 95 Hz vertical scan rate. (Check
with your dealer for recommendations, or check the "scan
rate, vertical" listings in our on-line catalog.)