Optoma BX-CTA28 Short Zoom Ultra Short Throw Lens for ZK1000, ZK1120, ZK1320

Optoma Genuine Lens BX-CTA28 Short Zoom is an OEM optical accessory for Optoma professional projectors. It is an Ultra Short Throw lens with a 0.34-0.37:1 throw ratio. The factory compatibility list covers 3 models: before installation, simply verify the projector model and panel size—no adapter rings or makeshift workarounds are needed. The value of a genuine lens lies not in the extra rows of specifications, but in the fact that it is calibrated from the outset for the optical path and mount of that projector series. Once installed, image-circle coverage, edge illumination, and focus travel are all delivered as designed, with no need to use keystone correction to compensate for image quality.

I. Lens Specifications

The specifications above are subject to the manufacturer's official specifications. For mechanical dimensions, flange distance, and mount type not shown in the specifications table, please contact us with your projector model. Ordering based solely 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 genuine lens is a zoom lens (0.34-0.37:1), 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 clear distances from the front surface of the lens to the screen and do not include space for rear housing ventilation and cable connections. These figures are calculated for a 16:10 aspect ratio; actual distances should be verified by on-site measurement and in accordance with the manufacturer's manual.

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

III. Compatible Models (3 Models)

The following table is taken from the factory compatibility list. Brightness and resolution are populated from the model database; entries that cannot be verified are marked “—” and are not estimated.

To determine whether a model outside the list can be used, please send us photos of the projector nameplate and existing lens for verification—models on the same-generation platform often share the same mount, but the risks of ordering based on a similar model outweigh the convenience.

Throw Ratios by Model Series

When the same BX-CTA28 Short Zoom lens is used with the series listed below, its rated throw ratio varies. Select the value based on the actual projector series.

IV. Three Checks Before Replacement

• Confirm the projector chipset 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.
• Calculate the installation distance first. This lens has a rated throw ratio of 0.34-0.37:1. Use the table in Section II to determine the distance for your venue; a prime lens has no margin, and even a zoom lens requires a 10–20 cm margin at both ends.
• Verify the mount and locking mechanism. The genuine lens is calibrated for the mount of that projector series, and you must hear it lock fully into place after installation. A skewed image or soft edges are usually caused by incomplete locking, rather than a problem with the lens itself.

If you are unsure, send us one photo of the projector nameplate and one of the existing lens nameplate. Verification against the actual products is the safest approach.