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Discussion Starter #1
After much tweaking, It's time to address this issue on my Davis clone PJ. The image's focus is uneven vertically! I'm one of those that puposefully blur the image to make the pixels not noticeable. The problem is, the top half of the image lags the bottom half in focus. I have to set the amount of defocus in reference to the top half of the image, and when I get the top half right, the bottom half becomes way too out of focus. If I set the defocus to suit the bottom half, the top half is pretty much in focus. There is no specific dividing line between bottom and top half, the non uniformity in focus between the halves is gradual. Anyhoo, would adjusting the alignment of the focus/zoom lens do the trick? I have moved that particular assembly out of the way once to clean out some dust in that area, but I don't remember when I noticed the problem with the focus, whether before or after I messed around with the lens. Any ideas is much appreciated!


Gerald
 

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Uneven focus means that you are not optically square with the screen. If the screen is fixed, change the angle and position of the projector.
 

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It was the same with my Davis DL450. I could not get an even focus vertically. I think it was a combination of things, the offset angle of the throw, the keystone correction and others. i don't think you can ever get an evenly focussed image on any projector that has an offset angle.
 

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I'm currently using an LP350 that has the same problem. It's not the position of the projector or the screen, it's defective or substandard optics. Period. During video it's unnoticeable, but on my computer desktop the icons along the left side are blurry. Very annoying. Thankfully my new LT-150 has perfect focus over the entire screen. http://www.avsforum.com/ubb/smile.gif
 

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Discussion Starter #5
Thanks for the info guys! Dfriend, you are correct! I have tried positioning the PJ by hand once to correct the focus. Even after extreme keystoning, it still wasn't even. I'm glad to know that it might not be anything I have done to the PJ, and that others have seen or are seeing the same thing with their PJs. Thanks again!
 

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For the record, keystoning on a digital projector does nothing other than degrade your image. TO my knowledge, there are no Digital machines with an Optical keystone correction.


When you adjust the keystoning on an LCD or DLP what you do is electronicallymanipulate the image. as a result, its ability to resolve a line is limited. THis results in SERIOUS JAGGIES all over the image. YOur de-interlacer does a great job, but then a projector adds jaggies...


In order to get a completely in focus field, you need to ensure that the machine is optically alligned with the screen. Or Manufacturers need to start using lenses that have a little deeper depth of field.


Essentially, if there is a focus issue from top to bottom, then the projector would need to be moved down, then tilted up a bit, or the other way around. As the lenses have very low f-stops, this adjustment can be quite minor. But it is the only way to create a "perfect" focus of your image.


For anybody with a longer memory that has been involved in the av industry for a while, isn't this reminiscent of Multi-image?
 
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