Christie CT Roadster 1.45-1.8:1

The CT Roadster 1.45-1.8:1 lens is a standard lens with a throw ratio of 1.45-1.80:1.
The lens is suitable for Christie 3-Chip DLP projectors.

How do I determine the correct value?

Distance = image width x Throw ratio
Image width = Distance / Throw ratio
Throw ratio = Distance / Image width

Lexicon

f-NUMBER
f stands for “focal length” (Brennweite). The ratio of focal length to the aperture opening. Zoom lenses often have two values. The large apertures are described with small numbers and the small apertures with large numbers. A lens with a lower f-number lets more light through.

PROJECTION RATIO
Also called projection ratio, throw. It describes the ratio of the projection distance to the image width. The product of the number with the screen width is the distance between the projector and the screen. Therefore the width of the screen can be calculated by dividing the projection distance by the number. If two numbers are given (e.g., 1.5-2.5:1), this means the projector has a zoom lens and the ratio can be altered within the specified range.

SCREEN SIZE (Diagonal)
Distance between two diagonally opposite corners.

ASPECT RATIO
Aspect ratio, the ratio of width to height

IMAGE RESOLUTION
Number of picture points (pixels) of the width and height of an image: e.g. 1920×1080

With a 4:3 aspect ratio
VGA (Video Graphics Array) 640×480 Pixel
SVGA (Super Video Graphics Array) 800×600 Pixel
XGA (Extended Graphics Array) 1024×768 Pixel
SXGA+ ( Super Extended Graphics Array Plus) 1400×1050 Pixel
UXGA (Ultra Extended Graphics Array) 1600×1200 Pixel

With a 5:4 aspect ratio
SXGA (Super Extended Graphics Array)

With a 16:9 aspect ratio
HD 720 (HD) 1280×720 Pixel
WSXGA (Wide Super Extended Graphics Adapter) 1600×900 Pixel
FULL HD (2K, HD1080, 1080p) 1920×1080 Pixel
QWXGA (Quadruple Wide Extended Graphics Adapter) 2048×1152 Pixel
2k 2048x1080 Pixel
4K-UHD 3840 x 2160 Pixel

With a 16:10 aspect ratio
WXGA (Wide Extended Graphics Array) 1280×800 Pixel
WXGA+ (Wide Extended Graphics Array Plus) 1440×900 Pixel
WSXGA (Wide Super Extended Graphics Adapter) 1680×1050 Pixel
WUXGA (Wide Ultra Extended Graphics Array) 1920×1200 Pixel