Sekonic Speedmaster L-858D-U Light Meter

The L-858D-U Speedmaster is a versatile light meter that supports both incident and reflected light readings for flash and ambient sources. With an extended measuring range of -5 to 22.9 EV at ISO 100 and an illuminance range from 0.1 to 2,000,000 lux, it excels in both low-light and high-intensity lighting conditions. The large 2.7″ color touchscreen LCD provides an intuitive interface for navigating settings and reading measurements. Its rugged, all-weather design ensures reliable performance even in challenging environments.

Equipped with a 270° rotating and retractable lumisphere, the meter adapts to different lighting angles and setups. An integrated 1° spot viewfinder allows for precise reflective readings from specific areas of a scene. The L-858D-U is uniquely capable of measuring flash duration from 1/40 to 1/55,500 second, using selectable t0.1 to t0.9 thresholds. It also supports high-speed sync (HSS), enabling accurate metering even when using modern TTL strobes at high shutter speeds.

Additional key features include a Flash Analyzing Function that displays the ratio of ambient to flash exposure, memory recall, and extensive cinema tools such as adjustable shutter angles (1–358°) and frame rates (1–1000 fps). The meter supports an ISO range from ISO 3 to 13,107,200, with a special ISO 850 setting. Expanded shutter speed options span from 1/64,000 second to 30 minutes for ambient light, and 1/16,000 second to 30 minutes for flash. Firmware updates, custom settings, and profiling are handled via a built-in micro-USB port.

Sekonic RT-GX Godox Transmitter Module

Included with this kit is the RT-GX Transmitter Module, which integrates seamlessly into the L-858D-U meter. This module enables full 2.4 GHz wireless control using the Godox radio protocol, offering compatibility with a wide range of Godox flashes and lighting systems. It provides access to 32 channels, 16 groups, and Wireless IDs for reliable triggering within a 98.4′ range.

The RT-GX module allows for more than just wireless triggering—it supports HSS flash metering, enables adjustment of modeling light power, and makes it easy to measure flash duration and ambient-to-flash light ratios in complex setups. For Godox users, this level of control dramatically improves metering precision and simplifies real-time lighting adjustments.