CRT Geometry

Slava

Distinguished
Mar 6, 2002
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My new 21” (non-aperture grille) Viewsonic G220fb monitor behaves strangely (or so I thought – please see below).

Example 1: In Photoshop 7.0 as I drag a (2D) image all the way to the left/right edge of the screen its width becomes greater compared to when the image is centered on the screen. The difference is about 5mm or 1/5 th of an inch.

Example 2: I have a WorldSaver 3D screensaver. It has the Earth in the center and the Moon orbiting the Earth. As the Moon moves closer to the left/right edge of the screen its shape changes from a perfect sphere to something that looks more like an egg than a sphere.

Example 3: In 3D games, such a s Knights of the Old Republic, if you are looking at a character in the center of the screen it looks thinner, but as you rotate the camera and the position of the same character moves close to the edge of the screen it becomes fatter.

At first I thought that the problem was specific to my 21” Viewsonic. The width distortions are pretty noticeable since the screen is so large.

However, when I measured the size of an image in Photoshop 7.0 on my office 19” aperture grille Trinitron I realized that the same thing happens on the 19” too (image width becomes greater the further away from the center of the screen you drag it) though the distortion is not that obvious on the Trinitron due to smaller monitor size.

I spent many hours playing with OSDs and read quite a few things on the internet but I was unable to resolve the problem.

Can anyone help? Are such distortions typical on large monitors? Before I got this Viewsonic I had a 21" SONY Trinitron (originally very expensive, but I got it on the cheap from a friend's medical office.) I did not notice any distortions on that SONY... It died, unfortunately.
 
This sizing effect is due to the dot pitch difference between the center and the edge of the screen. In the center the dot pitch is smaller i.e(0.25"), while on the edge of the screen the dot pitch is usually larger i.e(0.27"). This should not happen if you have a monitor with the same dot pitch throughout the whole screen. Hopes this helps to clarify.