JTX Lens & Pin-cushioning

Pin-cushioning is a term that describes the geometric distortion that is caused when the edges of a projected image appear to pull inward towards the center. In prism based anamorphic lenses it is described as looking like an “hour glass” lying on its side.

HOW TO MINIMIZE THE EFFECTS OF PIN-CUSHIONING
All two prism setups introduce some amount of pin-cushioning. This effect is minimized in the four following ways:

1. Proper Alignment of the Anamorphic Lens
The anamorphic lens should be placed in such a way as to align the prism surfaces at a 90 degree angle to the center of the projected light path. This will not remove the “pin-cushioning”, but will distribute the effect evenly to the top and bottom of the projected image.

2. Projectors Throw Ratio
The extent to which pin-cushioning is introduced is affected directly by the relationship of the projectors distance to the screen and the projected image size, also known as the throw ratio. The longer the projectors throw (larger throw ratios) the less pin-cushioning is introduced, likewise, the shorter the projectors throw (smaller throw ratios) the greater the effects of pin-cushioning.

This means that to minimize the effects of pin-cushioning, the projector needs to be positioned as far to the rear of your theater as possible, but still allowing for desired image size. In the end, the amount of pin-cushioning caused by the JTX Dual Prism Anamorphic Lens will depend on each individual’s theater setup.

3. Use of a Flat Screen
On a flat screen the recommended method for dealing with pin-cushioning is to make sure your screen is bordered by 3 to 4 inches of black material or paint. Many commercial screens come with frames covered in such material. The projected image can then be zoomed in or out to allow for the corners to “overscan” on to the blackout material. This is very common and is universally accepted.

4. Use of a Curved Screen
Many have found that using a curved screen not only creates a more immersive theater experience, but also resolves the pin-cushoning effect. A curved screen works to counter the effect of pin-cushioning in the following way: pin-cushioning results in images that have a greater vertical height at right and left edges. A curved screen, where the edges of the screen bend toward the audience, results in images that have less vertical height at the right and left edges. When applied correctly, these two effects counter act each other and provide for a uniforn vertical height across the entire projected image.