Optoma BX-CTA25 Zoom Standard-Throw Lens Analysis: Compatibility with ZK1050 and ZK750

Optoma Original Lens BX-CTA25 Zoom is a factory-supplied optical accessory for Optoma professional projectors. It is a standard-throw lens (Standard Throw) with a throw ratio of 0.85-1.02:1. The factory compatibility list covers 2 models, so verify the projector model and panel size before installation—no adapter-ring workaround is needed. The value of an OEM lens lies not in the extra figures in the 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 designed values, so there is no need to use keystone correction to compensate for image quality.

I. Lens Specifications

These specifications are subject to factory standards. Mechanical dimensions, flange distance, and mount type not shown in the table should be verified with us using your projector model; 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 OEM lens has a zoom function (0.85-1.02:1), so a given image size corresponds to a range of installation distances, and the lens can focus anywhere within that range.

These figures represent the clear distance from the front of the lens to the projection screen and do not include clearance for rear ventilation and cable connections. They are calculated based on a 16:10 image format; actual values are subject to on-site measurements and the factory manual.

Image quality differs at the two zoom positions: toward the short-throw end, the image is brighter and the edges are slightly less sharp; toward the long-throw end, the edges are sharper and brightness decreases slightly. Where the venue allows it, use the middle of the range. After installation, find the sharpest setting on the focus ring, then fine-tune the lens shift.

III. Compatible Models (2 models)

The table below is taken from the factory compatibility list. Brightness and resolution are populated from the model database; unavailable values are marked as 「—」 and are not estimated.

To verify whether a model outside the list is supported, send us photos of the projector nameplate and the current lens. Same-generation platforms often share the same mount, but ordering based solely on a similar model number is not worth the risk.

Throw Ratios by Model Series

The rated throw ratio varies by projector series, even when the same BX-CTA25 Zoom lens is used. Select the value based on the series of the actual projector.

IV. Three Checks Before Replacement

• Confirm the projector chip and resolution. The OEM lens is designed for a specific panel size. If the panel specifications differ, its image circle will not cover the full image, resulting in vignetting or light loss at the edges.
• Calculate the installation distance first. Use the table in Section II to match the lens's rated throw ratio of 0.85-1.02:1 to your venue dimensions. A fixed-focus lens offers no margin, and even a zoom lens requires 10–20 cm of clearance at both ends.
• Verify the mount and locking mechanism. The OEM lens is calibrated to the mount of that projector series. After installation, you must hear it lock into place. A skewed image or soft edges are usually caused by incomplete locking, not by a fault in the lens itself.

If you are unsure, take one photo of the projector nameplate and one of the current lens nameplate and send them to us. Verification against the actual units is the most reliable approach.