Projector convergence and focus are both important parts of an impressive home theater. Unfortunately,
historically available test paterns do not provide a way to easy differentiate between the two. That's where
these patterns come into play.
Focus determines how well the projected image (as viewed on the screen) matches the image cretaed by its core technology (LCD, LCOS, DLP, etc.). On the other hand, convergence is an attribute of the of the projector's core technology and the manufacturer's quality tolerances. In the case of all technologys except DLP, the image is created from 3 separate elements: one for red, one for greeen, and one for blue. These elements are optically combined. Sometimes they are combined better than others.
So how do you know if you have a focus problem or a convergence problem? A test pattern with only one of the primary colors is required (red, green or blue). By definition there can be no convergence issue if only one of the elements is in use. Convergence shouldn't be checked until the projector's focus has been characterized and any poor regions identified.
Convergence is exaimined through the use of multiple patterns each utilizing only 2 of the elements (example: red and green, green and blue). A final convergence check is done using all 3 elements (red+green+blue=white). Using
patterns with only 2 elements allows the convergence of these 2 elements to be compared relative to each other. With perfect convergence, when 2 elements emit the exact same image then the combined image should show each element's image exactly on top of the other. This is how the projector creates colors using the addative RGB color model. For final checking, a white pattern is used (red+green+blue).
While there are many ways to utilize these test patterns, one suggestion is summarized below.
Select the Green Dot pattern
Scroll or position the test pattern to fill your projector's display. You can click on the test pattern to make it full screen
Adjust the focus on your projector until the dots in the center are as sharp as possible
Closely exaimine all the other dots. If they are not as sharp as the dots in the center, your projector has inconsistent focus and this will effect the image displayed regardless of convergence
Without adjusting theh focus, you want may want to display both the Red Dot pattern and the Blue Dot pattern. You should see the same level of dot focus as you saw with the Green Dot pattern. If not, your projector has inconsistent focus across it's elements. This can easily be confused with poor convergence.
Now it's time to check convergence. Select the Red/Green Pluses. If the projector's red and green elements are manufacturered percisely, you should see yellow pluses with no fringing. Note: the displayed plus will never appear to have good convergence if the focus showed problems in that area
Repeat with the Green+Blue plus signs. You should see aqua pluses with no fringing
If no fringing was visible with Red+Green pluses as well as with the Green+Blue pluses, only then will the R+G+B pluses show solid white with no fringing
1080p Focus / Convergence Controls
1/24/2013: First Release
1/27/2013: Added background grayscale selection. Note that changing background automatically redraws current pattern
1/28/2013: Added fullscreen support. Click on the displayed test pattern to enable/disable
1/29/2013: Tweaked to work with Internet Explorer (already worked with Safari, Firefox and Chrome). Note: No fullscreeen support with IE
1/31/2013: Added some instructions / overview
7/22/2015: Updated slightly