Scheimpflug: Exotic Delicacy or Angle Correction?
Scheimpflug is one of those words that brings to mind a number of different images. Its been described as many things, from sushi to weather balloons. However, our initial mental image of scheimpflug was of a German baritone brass horn.

In reality, scheimpflug is a correction which allows the image from a large screen projector to be uniformly focused from top to bottom and left to right, even though the lenses are not perpendicular to the screen.

Projection lenses have a very wide aperture and are very fast in nature. The wide aperture allows a lot of light from the phosphors of the CRTs to pass to the screen. The down side of this is that all three lenses must be perfectly on-axis to both the object (CRT) and the image (screen) or the image focus will not be uniform from edge to edge. Generally, multi-lensed projectors have poor depth of focus capability.

Large screen multi-lensed projectors have their lenses aimed down if ceiling mounted and up if table mounted -- usually between 10.5 and 12.8 degrees. In addition, the red and blue lenses are aimed inward toward the center of the screen in order to converge with the green at the screen. These non perpendicular projection angles would normally produce an unfocussed mess on the screen if it were not for scheimpflug correction.

The correction is done by creating and angle between the object (CRT) and the lens, which cancels out the angle between the lens and image (screen). This correction is found in all projectors but most often is achieved via the use of shims or permanent molding.

Several different projector manufacturers have continuous scheimpflug adjustment. It is done mechanically with screws or concentric dial/spacers depending on the manufacturer. Although it is possible in some cases to replace shims with different sized shims on non continuous scheimpflug projectors, there is no way to easily calculate the shim thickness. Continuously adjustable scheimpflug systems usually offer much more range than could be achieved via shim replacement.

As an added note, none of the liquid light valve projectors have continuously adjustable scheimpflug correction. They don't need them because they have the luxury of narrower aperture, slower and longer throw lenses. They do not have a depth of focus limitation. They can do this because of the extra lumens available.

For more information on scheimpflug, call Cheryl Walker, VP-Marketing at 407-260-5511 or email her at Solutions@genproj.com