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Keystone vs. Optical Shift

post #1 of 4
4/6/09 at 10:32pm
Thread Starter 
I am building a dedicate home theater in my home, and I have completed most of the design work. One of the last details I am working through is the projector position. I have a 100” 16:9 screen and the Panasonic AE3000.

I have read that it is better to shift the image (optical) versus using the keystone (digital), so I am considering having the projector mounted further from the ceiling than may be asthetically pleasing. So, my questions are:

1.How important is it to reduce/eliminate keystone versus image shifting? Should I position the projector so keystone is zero?
2.Should I try to mix the two, e.g., 10 degree tilt/keystone with some image shift?
3.Lastly, how important is the distance between the screen and projector? It will be located within the recommended range of 10 to 19 feet for a 100” screen, but is it better to be at the low end of the range?
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post #2 of 4
4/7/09 at 5:58am

Re: Keystone vs. Optical Shift

The smaller the image is when be projected through the lense, the less distortion there will be. (the further back the better).

Usually you can find a sweet spot around the mid to 3/4 back range of the zoom.

When adjusting, put up a convergence grid and look for convergence error, and also focus uniformity. Move the PJ forward and backwards until you find the best fit position.

NEVER USE ANY DIGITAL KEYSTONE OR DIGITAL SIZING CONTROLS. Even 1 click will kill your resolution and create a bunch of artifacts. If you are considering using these controls, just get a 720 p PJ as you will be wasting your money on 1080p.
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post #3 of 4
4/7/09 at 9:07am

Re: Keystone vs. Optical Shift

Digital keystone correction is commonly used in portable projectors for stationary computer images, such as PowerPoint presentations by traveling salespeople. They have to make a reasonably recognizable image in a wide variety of rooms, projector locations, screen types (bare walls included), and viewing conditions. Moving images are not the priority, mostly graphs, text, spreadsheets, still photos, etc. The feature is provided to correct the overall geometry of the image- with loss of resolution, disrupted motion, moire', and similar artifacts considered as acceptable compromises.

Many projectors sold for home theater use are modified business class units. This is especially true of the cheaper models. Seldom are projectors designed from the ground up to display video optimally. Therefore, keystone correction is a feature retained on many home theater models by default. It should not be necessary for permanent installations or where fine resolution and moving images are the priority.

Best regards and beautiful pictures,
G. Alan Brown, President
CinemaQuest, Inc.
A Lion AV Consultants Affiliate

"Advancing the art and science of electronic imaging"
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post #4 of 4
4/7/09 at 12:36pm
Thread Starter 

Re: Keystone vs. Optical Shift

Thanks for the responses. I'll lower the projector to avoid keystone!
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