on February 06, 2024


Astronomical observation, especially of solar events like eclipses, is a fascinating yet challenging endeavor that requires the right equipment for both safety and clarity. Dr. Michel Willemin, an enthusiast with a profound understanding of astronomical observation, recently shared his experience testing the Marumi EXUS ND100000 (5.0) solar filter. This article aims to summarize his findings and underscore the importance of using appropriate solar filters for the upcoming total solar eclipse on April 8, 2024, observable across the American continent.

Background Information

Solar filters are essential for observing the sun directly, protecting both the observer's eyes and the camera sensor from intense sunlight. With the total solar eclipse approaching, understanding and selecting the right filter becomes paramount for enthusiasts eager to witness this celestial phenomenon.


Experiment Set up

Dr. Willemin's setup included the Marumi EXUS ND100000 filter, a Canon EF 400mm telelens, an IR/UV cut filter, a ZWO ASI678MC camera, and a SkyWatcher HEQ5 Pro mount. Despite less-than-ideal sky conditions and a low solar elevation, the initial testing offered promising insights into the filter's performance.


Set up for solar observation
[List of equipments]
  • Solar filter Marumi EXUS ND100000 (5.0)
  • Telelens Canon EF 400mm f/5.6 L
  • IR/UV cut filter
  • Camera ZWO ASI678MC (He used this planetary camera, but a standard mirrorless camera would also work well)
  • Mount SkyWatcher HEQ5 Pro


Observations and Findings by Dr. Willemin

The Marumi EXUS ND100000 provided excellent contrast and nearly neutral colors, showcasing a significant improvement over metallic filters about the Stehl ratio. The Schott B270i glass's optical quality was highlighted, suggesting a superior viewing experience for solar observation.

The limb darkening of the sun is fully normal, and this filter is revealing it perfectly.

 First image of the sun on February 3, 2024 @ 14:31UTC with Marumi EXUS (left) and the reference of SDO/HMI (right)

He highly recommends the Marumi EXUS ND100000 for observing the partial phases of a solar eclipse. Its ability to deliver high-quality images with accurate color rendition and contrast makes it an ideal choice for both seasoned astronomers and beginners looking to safely enjoy the eclipse.



Dr. Willemin's experiment with the Marumi EXUS ND100000 demonstrates its efficacy and suitability for solar observation during the eclipse. For those planning to observe the total solar eclipse in 2024, adopting Dr. Willemin's recommended equipment could enhance the experience, combining safety with exceptional visual clarity.


The solar and planetary observations specialist, Dr. Willemin

Dr. Michel Willemin, is an astronomical observation enthusiast from Preles, Switzerland. Dr. Michel Willemin's website showcases his passion for astronomy, providing insights into his projects and interests in this field. It serves as a platform for sharing his work and observations, emphasizing his engagement with the astronomical community.