Getting an Acer external monitor to work with a MacBook Pro

Can you alter the refresh rate (Hz) on the Monitor?

When you open System Preferences/Display on that Monitor it shows you the settings for it. The [Refresh Rate] option is under [Colors] - is it greyed out as [n/a] or does it show 70Hz, 60Hz etc. ? (I'm not sure this is the cause of the graininess but it's worth a shot)

two possibilities>

1. you're using analog cable to connect to external display (via dvi to vga adapter-but that is not the case obviously, because otherwise you could set the ref. rate for 60 or 75Hz - now its greyed out) anyway, when I used this set up, I noticed huge degradation of displaying quality. kinda washed out and blurred. but not grain at all

2. but what is more presumable in your case, you're using photo background provided by apple...these pictures are grainy by themselve. and when you extend your desktop from 15" to 20" it's clear that you notice it, all the more, if the external is not widescreen, therefore background image has to be stretched and cropped even more, therefore the grain is even bigger. This is my personal experience.

try to test it. put to the background for example some gradient made especially for that purpose in ill or ps. make two versions for both screens.
thats all
good luck

what you need? you need to do what i told you. aa ok. you have to find out the exact resolution of external display of course. then make a new document in photoshop with this size, with 72dpi resolution and stretch a gradient. set as a background picture. you'll see that there's no grain anymore. at least I suppose. it really is the thing of a photos in original apple library. actually there's nothing you can do. just change the picture of a background. actually you were writing that you work with graphics, so you already know what im writing here...
anyway, is that grain apparent also when you work with your own graphics?

I was having similar issues; looks like the MBP will not drive the external monitor at it's highest resolution unless you close the lid of the MBP; then, resume from sleep using your external keyboard. This will give you a full resolution output to the external monitor but you will not have any display on the laptop LCD.

Leaving the MBP closed while working on the external monitor isn't a good idea due to the heat build up.

Here is some information that was helpful to me.

http://www.livingdigitally.net/2006/10/usinganextern.html

What resolution is the acer? I use a 19 Samsung widescreen with mine and while it is not crystal clear its not grainy. Thats with DVI no adaptors. Also this is while mirror display or using the Acer as extra desktop?