BenQ LS1ST4 Ultra Short Fixed Lens Guide: LU9750, LU9800, LU9915

BenQ Genuine Lens LS1ST4 Ultra Short Fixed is an original optical accessory for BenQ engineering projectors. It is an ultra-short-throw (Ultra Short Throw) lens with a 0.38:1 throw ratio. The manufacturer's model compatibility list covers 3 models; before installation, simply verify the projector model and panel size—no adapter ring is needed. The value of a genuine lens lies not in the extra figures in its specification sheet, but in the fact that its optical path and mount are calibrated for that projector series at the factory. Once installed, the image circle, edge illumination, and focusing travel all meet their designed values, eliminating the need to use keystone correction to compensate for image quality.

I. Lens Specifications

Brand	BenQ（BenQ）
Lens Model	LS1ST4 Ultra Short Fixed
Throw Ratio	0.38:1
Product Type	Ultra Short Throw (Ultra Short Throw)
Compatible Models	3 models
Warranty	12 months; after-sales service is available for damage not caused by user error, based on the date on the shipping invoice

The above specifications are subject to the manufacturer's official specifications. For mechanical dimensions, flange distance, and mount type not listed in the specification table, please contact us with the projector model for verification. Placing an order based solely on a similar model carries the risk that the lens will not fit.

II. Calculating Installation Distance from Throw Ratio

The throw ratio is the ratio of installation distance to image width. This genuine lens has a fixed focal length (0.38:1), so the installation distance varies linearly with image size, with no adjustment margin. Accurate measurements are essential before installation.

Image Size	Image Width	Required Installation Distance
100 inches	2.15 m	approx. 0.82 m
120 inches	2.58 m	approx. 0.98 m
150 inches	3.22 m	approx. 1.23 m
200 inches	4.30 m	approx. 1.63 m

The distances above are clear distances from the front surface of the lens to the screen and do not include space for rear projector ventilation or cable connections. These values are calculated for a 16:10 image; actual distances should be verified through on-site measurement and in accordance with the manufacturer's manual.

III. Compatible Models (3 Models)

The following table is taken from the manufacturer's model compatibility list. Brightness and resolution have been populated from the model database; unavailable data is shown as "—", with no values inferred.

Model	Brightness	Resolution
LU9750	8500 lumens	WUXGA,1920 x 1200
LU9800	10000 lumens	WUXGA,1920 x 1200
LU9915	10000 lumens	WUXGA, 1920 x 1200

For compatibility with models not included in the list, please send us photos of the projector nameplate and the current lens so we can verify them. Platforms from the same generation often share the same mount, but ordering based on a similar model name is not worth the fitment risk.

Throw Ratios by Projector Series

The nominal throw ratio of the same LS1ST4 Ultra Short Fixed lens varies by projector series. Use the value corresponding to the series of your actual projector when selecting.

Projector Series	Throw Ratio
—	0.38:1

IV. Three Checks Before Replacement

• Confirm the projector 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 light loss after installation.
• Calculate the installation distance first. This lens has a nominal throw ratio of 0.38:1. Use the table in Section II to calculate the distance for your installation site. A fixed lens has no adjustment margin; even when using a zoom lens, allow 10–20 cm at both ends.
• Verify the mount and locking mechanism. The genuine lens is calibrated to the mount used by that projector series. After installation, you must hear it lock securely into place. A skewed image or soft edges usually indicate that the lens is not fully locked, rather than a problem with the lens itself.

If you are unsure, take one photo of the projector nameplate and one of the nameplate on the current lens, then send them to us. Verification against the physical products is the safest approach.