Throw ratio equals the throw distance divided by the unexpanded, prelens screen width (D/W). It is one way to express the zooming capability of projector. Due to the finite lens opening, anamorphic lens has a specified working throw ratio range. The lowest value (largest picture) is usually limited by the lens, even if the projector's zoom would allow smaller throw ratios. The lowest value is also dependent on how close the lens can be attached to the projector's optics. The recessed projector optics forces the low limit of ratio significantly bigger. Also the use of lens shift or if the projector has a large, native optical offset, the working low end of throw ratio range may slightly be increased. It is also good to note that due to focus forrection element, the P-100 series lenses decrease the throw ratio around 5% from the definition. In performance point of view the recommended throw ratio is somewhere from 2.0 to 2.5.
You can check the throw ratio range of you projector from the user manual or here
COMPATIBILITY WITH PRISMASONIC LENSES:
P-100 series
Non-recessed projector optics -> Throw ratio larger than 1.5 -1.6,
Recessed projector optics -> Throw ratio larger than 1.8 - 2.0
C-100 series
Non-recessed projector optics -> Throw ratio larger than 1.25 -1.35,
Recessed projector optics -> Throw ratio larger than 1.5 - 1.6
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