EIKI AH-AC21020 Zoom Long Throw Lens Compatible with EK-831DU, EK-831U, EK-833DU, EK-836DU

Eiki Original Lens AH-AC21020 Zoom is an original optical accessory for Eiki professional projectors. It is a long-throw (Long Throw) lens with a throw ratio of 1.61-2.42:1. Eiki's official compatibility list covers 4 models; before installation, simply verify the projector model and panel size—no need to make do with adapter rings. The value of an original lens lies not in the extra figures in the specification sheet, but in its factory calibration to the optical path and mount of that model series: once installed, the image circle, edge illumination, and focusing range all meet their design specifications, so there is no need to use keystone correction to compensate for image quality.

1. Lens Specifications

Brand	Eiki（Eiki）
Lens Model	AH-AC21020 Zoom
Throw Ratio	1.61-2.42:1
Product Type	Long Throw
Compatible Models	4 models
Warranty	12 months; coverage for damage not caused by the user is available through after-sales service, based on the date on the shipping invoice

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

2. Converting Throw Ratio to Installation Distance

The throw ratio is the installation distance divided by the image width. This original zoom lens (1.61-2.42:1) supports a range of installation distances for any given image size, and it can focus anywhere within that range.

Image Size	Image Width	Required Installation Distance
100 inches	2.15 m	approx. 3.46 – 5.20 m
120 inches	2.58 m	approx. 4.15 – 6.24 m
150 inches	3.22 m	approx. 5.19 – 7.80 m
200 inches	4.30 m	approx. 6.92 – 10.41 m

These are clear distances from the front face of the lens to the screen and do not include space for cooling and cable connections at the rear of the projector. Calculated for a 16:10 image, actual distances are subject to on-site measurement and Eiki's manual.

Image quality differs at the two ends of the zoom range: at the shorter-throw end, the image is brighter and the edges are slightly softer; at the longer-throw end, the edges are sharper and brightness is slightly lower. Where site conditions allow, use the middle of the range. After installation, first find the sharpest setting on the focus ring, then fine-tune the lens shift.

3. Compatible Models (4 Models)

The table below is taken from Eiki's official compatibility list. Brightness and resolution are populated from the model database; any values that cannot be obtained are shown as “—” and are not estimated.

Model	Brightness	Resolution
EIKI EK-831DU	—	—
EIKI EK-831U	—	—
EIKI EK-833DU	—	—
EIKI EK-836DU	—	—

For compatibility with models not on the list, send us photos of the projector nameplate and current lens so we can check—platforms from the same generation often share a mount, but ordering solely because the model numbers are similar is not worth the risk.

Throw Ratio by Model Series

When the same AH-AC21020 Zoom lens is used with the series listed below, the specified throw ratio differs; use the value for the actual projector series.

Model Series	Throw Ratio
—	1.61-2.42:1

4. Three Checks Before Replacement

• Confirm the projector chip and resolution. The original 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.
• First, calculate the installation distance. This lens has a specified throw ratio of 1.61-2.42:1; use the table in Section 2 to calculate the distance for your venue. Prime lenses offer no adjustment margin, and even zoom lenses require a 10–20 cm allowance at both ends.
• Verify the mount and locking mechanism. The original lens is calibrated to the mount of that model series, and you must hear it click into the locked position after installation. A skewed image or soft edges are usually caused by incomplete locking, not a problem with the lens itself.

If you are unsure, send us one photo each of the projector nameplate and current lens nameplate; verification against the actual hardware is the safest approach.