Keystone projectors projector models and projector keystone is an effect of poor centring of screen.

Keystone projector

8mm projector or Keystone 8mm projector value is a keystone movie projector that is used for playing old movies that are on rolls in the 8mm format. This projector and many others can be bought on eBay. Picture of keystone projector.

These projector are now very rear.

Projector keystone

Whereas projector Keystone effect which is also known as tombstone effect is when an image is being projected on an exterior at a position not well centred into the screen. It could be due to the room arrangement causing the projector to be installed on one side or slanted aloft or down to fit in space. The angle created in the process will made the image to appear trapezoid.

Here the projector is slopped down and slopped up. On table projectors larger images at the top is common keystone problem.

Here the projector is slopped to either right or left.

The keystone problem can be solved by a keystone corrector a feature most if not all digital projectors have.

There are 2 ways of correcting keystone, manually or digitally. Some projectors have inbuilt keystone corrector which could be only upright while others can be both upright/perpendicular and parallel. Pricewise those offering only horizontal/parallel keystone correction are dearer in price.

In the digital projectors users turn the feature on to adjust the keystone in order to obtain a squared image.

Correcting perpendicular keystone

Correcting parallel keystone

When correcting the keystone manually the projector lenses is moved by hand so that the projector projects at either at a higher angle or lower angle. In manual keystone removing there is no parallel keystoning. The projector distance needs to be a bit far from the screen or viewing surface.

Advantages and Problems with keystoning

For people presenting on the move, it is a must for them to correct the keystone to get centres image alignment. There are many limitation for these people including wall not being upright, the projector could be positioned only on lower or higher cushion than the bottom of the screen. In such situations keystone correction purpose is in advantageous.

The degree to which projectors can provide keystone correction vary some as little as 12 degrees to as much as 35 degrees of alteration. The downside to keystone correction is that picture quality is lot especially at the sided where the correction was done. This can be caused by both keystone correction and lens shift.