BenQ LS1LT2 Long Zoom 1 Long-Throw Lens Guide: LU9750 LU9800 LU9915

BenQ Original Lens LS1LT2 Long Zoom 1 is a factory-supplied optical accessory for BenQ engineering projectors in the long-throw (Long Throw) category, with a throw ratio of 3.58:1 - 5.38:1. The factory compatibility list covers 3 models. Before installation, simply verify the projector model and panel size; there is no need to improvise with an adapter ring. The value of an original lens lies not in the extra figures on a specification sheet, but in the fact that it is calibrated at the factory to the optical path and mount of that projector series. Once installed, the image circle, edge illumination, and focusing travel are all at their design values, eliminating the need to use keystone correction to compensate for image quality.

I. Lens Specifications

The above specifications are subject to the original manufacturer’s specifications. For mechanical dimensions, flange distance, and mount type not shown in the specifications table, please verify them with us based on the projector model. Ordering directly based on a similar model carries the risk that the lens will not fit.

II. Converting Throw Ratio into Installation Distance

The throw ratio is the ratio of the installation distance to the image width. This original lens is a zoom lens (3.58:1 - 5.38:1), so a given image size corresponds to a range of distances, and it can be focused at any installation distance within that range.

The above is the clear distance from the front surface of the lens to the projection screen and does not include space for rear cooling and cable connections. The figures are calculated for a 16:10 aspect ratio; actual values are subject to on-site measurement and the original manufacturer’s manual.

Image quality differs at the two ends of the zoom range: toward the near end, the image is brighter and the edges are slightly softer; toward the far end, the edges are sharper and brightness is slightly lower. Where the venue allows, it is recommended to aim for the middle of the range. After installation, first find the sharpest setting on the focus ring, then fine-tune the lens shift.

III. Compatible Models (3 Projectors)

The table below is taken from the factory compatibility list. Brightness and resolution are populated from the model database; where the data are unavailable, they are marked “—” and are not estimated.

For compatibility with models not on the list, please send us photos of the projector nameplate and the existing lens for verification. Platforms from the same generation often share the same mount, but ordering based on model similarity is not worth the risk.

Throw Ratios for Different Model Series

The specified throw ratio varies by series when the same LS1LT2 Long Zoom 1 is installed on the models listed below. Select the value based on the series of the actual projector.

IV. Three Checks Before Replacement

• Confirm the projector imaging chip and resolution. Original lenses are designed for a specific panel size. If the panel specifications differ, the image circle cannot cover the full frame, resulting in vignetting or edge light loss.
• Calculate the installation distance first. This lens has a specified throw ratio of 3.58:1 - 5.38:1. Use the table in Section 2 to calculate the distance based on your venue dimensions. A fixed-focus lens offers no adjustment range, while even a zoom lens should allow a 10–20 cm margin at both ends.
• Verify the mount and locking mechanism. The original lens is calibrated to the mount of that projector series, and you must hear the lock engage fully after installation. A skewed image or soft edges usually indicate incomplete locking rather than a problem with the lens itself.

If you are unsure, take one photo of each nameplate—the projector nameplate and the current lens nameplate—and send them to us. Verification against the actual items is the safest approach.