Stacking 2 projector together... Alignment Skill or Tips! Panasonic projector!


CB Mods
Premium Member
Fight Leukemia
Jul 16, 2005
Las Vegas
When stacking two images, it is always preferable to align them optically as much as possible before using any digital alignment (including only sending the projector its native resolution). So, to answer your question, my preference is to have the two projectors as close to each other as possible (one physically stacked on top of the other is ideal) and as close to perpindicular and centered to the screen as possible. When the two lenses are almost in the exact same starting position, then aligning them will be considerably easier. Using the internal grid test pattern, first fully align one projector (if ground supported, align the bottom projector first, or if hanging, align the top projector first); focus then lens shift. When you have this aligned properly, then open the shutter on the second projector (you may want to close the shutter on the first while you focus the second) and focus then lens shift to match. If you have the ability to have your grid be green on one and red on the other, then you will notice the grid turn yellow as they line up.

I should note that you do not want to do any alignment until the projector is fully warmed up. I will usually wait at least 20 minutes prior to alignment but they should definitely be at full operational temperature by 30 minutes. This is essential as the optics will shift slightly as the lens mount warms up.

A couple of reasons why you want to optically align instead of using the "chip set" or digitally aligning. The first reason is that the less processing the projector has to do, the less possibility of latency in the signal. This doesn't always matter with strict playback, but each part of the system that adds latency can make a difference when doing a live image or timing with audio. The second reason why I prefer the lens shift over digital alignment is the quality of the image. For instance, if I am sending the native resolution to the projector, but now I need to keystone correct, I will see that straight lines become jagged. If I have to shift the image or resize the image then I am not fully using each pixel which can make the image apear out of focus in parts. This becomes more apparent when the image is larger and you are closer to it. Also, when you shift an image in one direction, it will end up blanking a portion of the signal on one side and repeat the last line on the other side (sometimes) as it only has a certain amount of information being fed to it. This often does not do much to the overall image as the audience mainly pays attention to the center, but can be distracting depending on content.

There are going to be times when optical alignment is not possible or you cannot get the two projectors to perfectly line up. That's when I will use the digital alignment for the fine tuning.

Does this make sense? Did I explain the difference between lens shift and digital alignment that you understand the difference between the two?