Christie 121-139105-XX Zoom Lens Overview: LWU755-DS/LWU900-DS Compatibility

Christie Genuine Lens 121-139105-XX Zoom is a genuine optical accessory for Christie engineering projectors. It is a Long Throw lens with a throw ratio of 1.70-3.00:1. The manufacturer's compatibility list covers 2 models; before installation, simply verify the projector model and panel size—there is no need to make do with an adapter ring. The value of a genuine lens lies not in the extra rows in the specification sheet, but in the fact that it is calibrated at the factory to the optical path and lens mount of that model series: once installed, the image circle, edge illumination, and focusing range all meet their design values, so there is no need to use keystone correction to compensate for image quality.

1. Lens Specifications

The above specifications are subject to the manufacturer's official specifications. For mechanical dimensions, flange distance, and lens mount configuration not shown in the specifications table, please verify them with us using the projector model; ordering based solely on a similar model carries the risk that the lens will not fit.

2. Calculating Installation Distance from Throw Ratio

The throw ratio is the ratio of the installation distance to the image width. This genuine lens is a zoom lens (1.70-3.00:1), so a given image size corresponds to a range of installation distances; it can focus at any point within that range.

The distances above are net distances from the front surface of the lens to the screen and do not allow for ventilation or cable connections at the rear of the projector. They are calculated for a 16:10 image; actual distances should be verified on site and according to the manufacturer's manual.

Image quality varies at the two ends of the zoom range: near the close end, the image is brighter and the edges are slightly softer; near the far end, the edges are sharper and brightness decreases slightly. Where the venue allows, using the middle of the range is recommended. After installation, first find the sharpest position on the focus ring, then fine-tune the lens shift.

3. Compatible Models (2 models)

The following table is taken from the manufacturer's compatibility list. Brightness and resolution are populated from the model database; values that cannot be retrieved are shown as "—" and are not estimated.

To determine whether a model outside the list can use this lens, please send us photos of the projector nameplate and the existing lens for verification—same-generation platforms often share the same lens mount, but it is not worth the risk to order solely because the model numbers look similar.

Throw Ratio by Model Series

The rated throw ratio differs by model series when the same 121-139105-XX Zoom lens is installed, so selection should be based on the series of the actual projector.

4. Three Checks Before Replacement

• Confirm the projector's imaging panel and resolution. The genuine lens is designed for a specific panel size. If the panel specifications differ, the image circle cannot cover the full image, resulting in vignetting or edge illumination loss after installation.
• Calculate the installation distance first. This lens has a rated throw ratio of 1.70-3.00:1. Apply the table in Section 2 to your venue dimensions. A fixed lens provides no adjustment margin, and a zoom lens still requires 10–20 cm of margin at both ends.
• Verify the lens mount and locking mechanism. The genuine lens is calibrated to the lens mount of that model series, and you must hear it lock into place after installation. A skewed image or soft edges are usually caused by incomplete locking, not by a problem with the lens itself.

If you are unsure, take one photo of the projector nameplate and one of the existing lens nameplate and send them to us; verification against the actual items is the safest approach.