Inon Close-Up Lenses (UCL Series)

Manufacturer: Inon (Japan) Type: wet-mount close-up diopters Product line: UCL-330, UCL-165, UCL-100, UCL-90, UCL-67 Years active: 2004—present Mount systems: M67 thread, Inon LD bayonet, AD bayonet Depth rating: 60m (197ft)

Overview

The Inon UCL (Underwater Close-up Lens) series is a long-running line of wet-mount diopters that has been a mainstay of underwater macro photography since the mid-2000s. Spanning five models from the mild UCL-330 (+3 diopter) to the powerful UCL-67 (+15 diopter), the series offers a complete magnification ladder that can be used individually or stacked for extreme super macro work.

Inon’s UCL lenses are designed exclusively for underwater use — they do not function properly on land due to the optical calculations accounting for the water-glass-air interface (^[1]). The lenses use multi-element optical glass with anti-reflection coatings and achromatic elements to suppress chromatic aberration.

The UCL series was historically the most affordable option for underwater macro shooters, positioned below the SubSee diopter and later the Nauticam SMC/CMC in optical quality, but offering reliable performance at accessible price points. The M67 thread system ensured broad compatibility across housing manufacturers, and the ability to stack lenses via adapter rings gave users flexibility without purchasing multiple expensive optics.

Product Line

UCL-330 (+3 diopter) — ~2004

The mildest lens in the series, offering gentle magnification boost suitable for compact cameras and mild close-up enhancement with macro lenses.

• Underwater focal length: 330mm
• Construction: Single element
• Use case: Compact cameras, mild macro enhancement, stacking on stronger diopters for fine-tuning
• Mount: M67 thread
• Compatible with stacking on UCL-67 and UCL-90 via Lens Adapter Ring (^[2], ^[3])

UCL-165 (+6 diopter) — ~2004

The workhorse of the series and Inon’s most widely used close-up lens. Available in both M67 threaded (UCL-165M67) and Inon LD bayonet (UCL-165LD) versions, plus the earlier AD mount version (UCL-165AD).

• Underwater focal length: 165mm
• Magnification: +6 diopter equivalent
• Construction: Multi-element optical glass
• Use case: Standard macro enhancement for both compact cameras and SLR systems
• Mount: M67 thread (UCL-165M67), Inon 28LD bayonet (UCL-165LD), Inon AD mount (UCL-165AD)
• Compatible with Canon, Olympus, Panasonic, and other compact camera housings via Inon mount bases (^[4], ^[5])
• Frequently stacked with stronger diopters (UCL-67, UCL-90, Nauticam CMC) for additional magnification (^[6])
• Listed by Ikelite as compatible with their compact housings via M67 adapter (^[7])

UCL-100 (+10 diopter) — 2013 (discontinued)

A high-power close-up lens with premium optical glass, released in February 2013.

• Underwater focal length: 100mm
• Construction: 3 elements in 3 groups, optical glass, anti-reflection coating on all inner surfaces
• Larger lens aperture to minimize vignetting with 28mm-equivalent compact camera lenses
• Mount: M67 thread (UCL-100M67) and Inon LD bayonet (UCL-100LD)
• Later discontinued; superseded by the UCL-90 and UCL-67 (^[8], ^[9])
• Inon noted in later documentation that the UCL-100M67 was “discontinued” but still usable with certain compact setups (^[10])

UCL-90 (+11 diopter) — December 2017

A powerful close-up lens positioned between the UCL-165 and UCL-67 in magnification. Designed for both full-frame SLR macro lenses and compact cameras.

• Underwater focal length: 90mm (equivalent to +11 diopter)
• Maximum magnification: 2.23x (area ratio 4.98x) with 100mm macro lens for full-frame SLR
• Working distance: 69mm from front lens surface at minimum focus (with 100mm macro)
• Construction: 3 elements in 2 groups, HR (high refractive index) glass, achromatic internal lenses, anti-reflection coating
• Mount: M67 thread (UCL-90 M67) and Inon 28LD bayonet (UCL-90 LD)
• Release date: December 27, 2017
• Shares accessories with the UCL-67 (Lens Adapter Ring for UCL-67/90, M67 Flip Mount Adapter for UCL-67/90) (^[11])
• Can be stacked with UCL-165M67 via adapter ring for higher magnification (^[12])
• Used by forum members with Sony 90mm macro on Nauticam ports via flip adapter (^[13])
• Referenced alongside Canon RF 100mm macro setups (^[14])

UCL-67 (+15 diopter) — February 2017

The most powerful lens in the UCL series, designed primarily for 60-100mm macro lenses on full-frame SLR cameras.

• Underwater focal length: 67mm (equivalent to +15 diopter)
• Maximum magnification: 2.76x (area ratio 7.65x) with 100mm macro lens for full-frame SLR
• Working distance: 52mm from front lens surface (83.4mm from housing port surface) at minimum focus with 100mm macro
• Construction: 4 elements in 3 groups, high refractive index glass, achromatic lens elements, anti-reflection coating on all surfaces
• Size: diameter 70mm, length 37mm
• Weight: 340g in air / 227g underwater (M67 version)
• Mount: M67 thread (UCL-67 M67) and Inon 28LD bayonet (UCL-67 LD)
• Release date: February 4, 2017
• Optional Lens Adapter Ring allows stacking UCL-165M67 or UCL-330 on front for even higher magnification (^[15])
• M67 Flip Mount Adapter available for use with Nauticam and other flip holders (not compatible with holders of 57mm or smaller diameter) (^[16])
• Recommended by forum users as an alternative to Nauticam CMC-1 for Olympus 60mm macro setups (^[17])

Mount Systems

Inon’s UCL lenses have been available across three mount systems over the years:

1. M67 thread — The industry standard 67mm screw mount. Compatible with virtually all SLR macro ports and many compact housing adapters. The most versatile option.
2. Inon 28LD bayonet — A quick-release bayonet mount used with Inon’s LD Mount Base accessories on compact housings. Faster to attach/detach than screw mounts.
3. Inon AD mount — An older bayonet system for early Inon compact accessories (UCL-165AD). Requires an AD Mount Converter.

The M67 thread versions offer maximum cross-brand compatibility, while the LD versions are optimized for use within the Inon compact accessory ecosystem.

Stacking

A key feature of the UCL system is the ability to stack lenses for higher magnification:

• The Lens Adapter Ring for UCL-67/90 allows mounting a UCL-165M67 or UCL-330 on the front of a UCL-67 or UCL-90 for increased magnification (^[18], ^[19])
• Inon explicitly warns against stacking two high-power lenses (e.g., UCL-67 + UCL-100, or UCL-67 + another UCL-67) as this “significantly degrades image quality” (^[20])
• Community members regularly stack UCL-165 with other diopters including Nauticam CMC-2 and AOI UCL-09 for super macro on compact cameras (^[21])

Comparison with Competitors

vs. SubSee diopter

The SubSee (+5 and +10 models from ReefNet) offered higher optical quality than the earlier UCL-165 and UCL-330, with better chromatic aberration correction. However, the SubSee was more expensive and less widely available. The UCL-67 (+15) and UCL-90 (+11), released in 2017, exceeded the SubSee +10 in magnification power and offered comparable multi-element optical designs.

vs. Nauticam SMC/CMC

The Nauticam SMC/CMC series (from 2013) represents the optical quality benchmark. Designed from the ground up for underwater use with computer-modeled correction for air-water interfaces, the SMC/CMC delivers superior sharpness, contrast, and bokeh quality. However, Nauticam lenses cost significantly more (CMC-2: $290, SMC-1: $480+, SMC-2: $1,046 vs. Inon UCL models at roughly $100-350). Forum users describe the Inon UCL-90 as producing results “weaker” than the CMC-1 in terms of per-diopter optical quality but still useful and far more affordable (^[22]).

vs. AOI UCL-90 Pro

AOI, a Hong Kong-based manufacturer, released the UCL-90PRO (+18.5 diopter) in September 2022. It uses high refractive index glass and broadband multi-layer anti-reflection coating on all surfaces. It is lighter and reportedly brighter than the Inon UCL-90, though significantly more expensive. Forum users have compared it favorably to the Nauticam CMC-1 (^[23], ^[24]).

Compatibility

The UCL series has been a core part of Inon’s compact camera accessory ecosystem since 2004. Inon regularly publishes compatibility charts confirming UCL lens support for new camera/housing combinations:

• Canon PowerShot S1 / WP-DC30 housing (2004) (^[25])
• Canon WP-DC40 housing (2005) (^[26])
• Olympus PT-053/PT-051 housings (2012) (^[27])
• Olympus E-M1 Mark II / PT-EP14 (2017) (^[28])
• Sony RX100 series cameras (2016) (^[29])
• Olympus TG cameras with macro adapter (2015) (^[30])

For SLR systems, any macro port with M67 front thread accepts UCL M67 lenses directly. This includes ports from Nauticam, Subal, Aquatica, Sea & Sea, Isotta, and others.

Timeline

• 2004: UCL-165 and UCL-330 available as part of Inon’s compact camera accessory line (^[31])
• 2005: UCL-165AD announced for Canon WP-DC40 housing with AD Mount system (^[32])
• 2010: UCL-330 and UCL-165M67 compatible with Inon X-2 housing for Panasonic GF1 (^[33])
• 2013-02: UCL-100M67 and UCL-100LD released — 3 elements in 3 groups, premium glass (^[34])
• 2017-02: UCL-67 released — the most powerful in the series at +15 diopter, 4 elements in 3 groups (^[35])
• 2017-12: UCL-90 released — +11 diopter, HR glass, fills gap between UCL-165 and UCL-67 (^[36])
• 2017-12: UCL-100 confirmed discontinued; Lens Adapter Ring and Flip Mount Adapter renamed to cover both UCL-67 and UCL-90 (^[37])
• 2022-09: AOI releases UCL-90PRO (+18.5 diopter) as a third-party competitor using similar naming (^[38])

References

Wetpixel Live