Patent ID: 7777819

Claim:
A method of modifying a display apparatus by replacing in the display apparatus a first reflective image generator having first mechanical or optical properties with a second reflective image generator having second mechanical or optical properties, the display apparatus including: a primary relay lens arrangement having a fixed focal length; a visor; a display source arranged to image the primary relay lens arrangement; wherein the primary relay lens arrangement is arranged to transmit the image from the display source to the visor; and wherein the display source includes: a first image generator arranged to generate an image; and a first display source relay optical arrangement; wherein the first image generator is arranged to image the first display source relay optical arrangement; and the first display source relay optical arrangement has a first focal length which is selected according to the first mechanical or optical properties to transmit a correctly sized image to the primary relay lens arrangement; the method comprising: replacing the first image generator with a second different image generator; and replacing the first display source relay optical arrangement with a second different display source relay optical arrangement having a second different focal length which is selected according to the second different mechanical or optical properties to transmit a correctly sized image to the primary relay lens arrangement, and wherein the display apparatus further comprises a first output screen arrangement for matching a first numerical aperture of the first display source relay optical arrangement with a numerical aperture of the primary relay lens arrangement, the method comprising replacing the first output screen arrangement with a second different output screen arrangement which matches a second different numerical aperture of the second different display source relay optical arrangement with the numerical aperture of the primary relay lens arrangement.