TTL Flash Metering

Also known as: Through-the-lens metering, TTL vs manual strobe, automatic flash exposure
Related techniques: Strobe & Flash Photography

Overview

TTL (Through-The-Lens) flash metering is an automatic flash exposure system in which the camera evaluates a scene through its lens and communicates exposure information to the strobe, adjusting the strobe’s power output so the photographer does not have to set it manually. As Ikelite described it: “TTL or ‘Thru-the-Lens’ flash metering means the camera evaluates the scene and communicates exposure information directly to the compatible flash. The camera automatically adjusts the power output of the external flash so you don’t have to” (^[1]).

Underwater, TTL has been one of the most debated topics in the Wetpixel community. The technique works well for macro photography where the subject fills much of the frame, but has significant limitations for wide-angle work where large areas of open water can confuse the metering system. The community has broadly settled on manual exposure as the standard for serious shooters, while TTL systems have continued to evolve — particularly through third-party converter boards from companies like UW Technics and TRT-Electronics (^[2]).

History & Development

Film-Era TTL

TTL flash metering originated with film cameras. As Alex Mustard wrote in his 2006 editorial “The Trouble with TTL”: “Ever since TTL strobe control was introduced with the Nikonos V in 1984 the vast majority of images have relied on it” (^[3]). The Nikonos V offered direct through-the-lens flash metering via hardwired sync cord, and it worked reliably because the camera measured light reflected off the film plane during exposure. Land-based Nikon TTL flash fill was considered masterful technology (^[4]).

The Digital Incompatibility Problem (2002-2003)

The transition to digital SLRs created a fundamental crisis for underwater TTL. Digital sensors reflect light differently than film, breaking the old TTL metering systems entirely. As Alex Mustard explained: “TTL is tricky with digital because sensors don’t reflect light in the same way as film. Camera companies have been forced to develop new TTL protocols for their digitals, usually determining the required power output using pre-flashes. Unfortunately, traditional underwater strobes were not compatible with these pre-flash systems” (^[5]).

In June 2002, Wetpixel member scorpio_fish raised the alarm: “The existing D-SLR offerings from Seacam and UK Germany don’t or can’t provide TTL function with existing underwater strobes” (^[6]). Stephen Frink’s solution for the Seacam D1X was to house a Nikon SB-28DX land strobe underwater for TTL — a cumbersome workaround (^[7]).

Digital cameras also introduced preflash metering — sending test pulses before the main exposure — which triggered traditional slave strobes prematurely. Canon used E-TTL (one preflash), Nikon used D-TTL (preflashes read off the shutter curtain via 5 sensors), and later i-TTL (preflashes read via the 1005-segment viewfinder meter, with support for multiple flashes) (^[8]).

The D2X Hotshoe Syndrome (2005)

The complexity of digital TTL protocols created unexpected problems. The Nikon D2X suffered from a mysterious syndrome where images would “shoot, appear on the LCD, but never write to the CF card” — caused by interference from unused hotshoe pins. Stephen Frink documented the issue and Seacam’s fix: removing specific pins from the hotshoe connector depending on the strobe configuration. He noted that “the submersible strobes you have been using with your Nikonos or other housed cameras will not fire in TTL with the EOS1Ds. In fact, they may not work at all” (^[9]).

Cracking the Digital TTL Code (2004)

In January 2004, Aquatica announced they had “cracked the E-TTL code” for the Canon 300D Digital Rebel. Eric Cheng reported seeing Aquatica’s E-TTL to TTL bridge circuit board at the Boston Sea Rovers show, with the processing chips being programmed that very weekend (^[10], ^[11]).

Ikelite followed in September 2004 with their own eTTL-to-TTL bridge for the Canon 300D, enabling DS-50 and DS-125 SubStrobes to work in TTL mode. Eric Cheng reported the October availability date (^[12]). Peter Schulz beta-tested Ikelite’s Olympus 5050/5060 TTL circuitry, reporting: “The results were outstanding. For the first time ever I got perfect lighting under almost every imaginable condition” (^[13]).

Slave TTL and the INON S-TTL Revolution (2005)

The INON D-2000, introduced at DEMA 2004, took a fundamentally different approach called S-TTL (Slave TTL). Rather than using a converter board and sync cord, the D-2000’s flash tube was engineered to have the same rapid flash duration as a camera’s internal strobe. This allowed it to exactly duplicate the camera’s controlling signal via fiber optic cable. As INON explained: “The flash duration of the D-2000 is equivalent to camera’s internal strobe. This characteristic enables the D-2000 to be controlled by camera’s internal strobe from small flash to full dump” (^[14]).

Existing strobes like the Sea & Sea Z-220 and YS-90DX had flash durations roughly five times longer than the D-2000, making slave TTL unreliable with them. The D-2000 also featured an EV Compensator dial for fine-tuning exposure underwater — a major convenience over the alternatives (^[15]).

James Wiseman reviewed the D-2000 for Wetpixel, testing it with an Olympus C-5060 in PT-020 housing. He used the same methodology as his earlier Ikelite eTTL2 test — shooting at different f-stops and confirming that the strobe correctly varied its output to maintain consistent exposure (^[16]).

Simultaneously, Matthias Heinrichs’ Digital Adapter 2 (DA2) was the first popular slave TTL solution for compact digicams. It worked with many existing strobes and offered “recorded TTL” mode to avoid optical feedback, plus a user-settable gain factor for extending flash duration on larger strobes (^[17]).

”The Trouble with TTL” — Alex Mustard’s 2006 Editorial

In January 2006, Alex Mustard published a landmark editorial on Wetpixel titled “The Trouble with TTL,” which crystallized the growing sentiment among experienced digital shooters. His argument: “The irony of the situation is that most digital photographers tend to cast off the crutch of TTL as their digital experience grows. They rapidly realise that not only is manual strobe control ridiculously easy with the instant feedback of the cameras LCD screen, but it also empowers them with more creative control” (^[18]).

Mustard confessed his own journey: “When I first got my first digital SLR, a Nikon D100 back in 2002, I went to the expense and effort of housing a normal Nikon land flash so I could have TTL. I told everyone I needed it. But, like the reformed smoker I am now one of the most vehement critics of the necessity of TTL” (^[19]).

The article drew spirited responses. Comment author scorpio_fish called it “a great job of summarizing the echo chamber of Wetpixelian thought on TTL.” Eric Hanauer (ehanauer) countered that “the best light meter is the lcd display on the back of your camera.” James Wiseman offered a nuanced view, noting that TTL worked great for his wife’s macro shooting on their Bali honeymoon but they switched to manual for wide-angle. Perhaps most pointedly, commenter “bandit” pushed back against the professional photographers’ anti-TTL stance: “‘It is not intended to be easy when done right’. That has to be the most condescending comment I have ever heard” (^[20]).

In December 2006, Mustard highlighted a forum thread “TTL In 2007” that revisited the question two and a half years after the original “TTL Anonymous” thread, asking whether the march of technology had made widespread TTL adoption viable (^[21]).

How TTL Works Underwater

The fundamental principle of TTL flash control is managing the duration of the flash pulse. As Pavel Kolpakov of UW Technics explained in his 2021 article on Wetpixel, the key is that “the luminous flux turns on and off almost instantly, in response to the presence or absence of energy supplied to the tube.” In manual mode, the photographer sets duration via a dial switch on the strobe body. In TTL mode, the TTL control system inside the housing sets it automatically (^[22]).

Modern digital TTL operates through these steps:

1. Preflash: The camera fires a low-power test pulse through the strobe
2. Metering: The camera’s TTL meter measures light reflected from the scene through the lens
3. Calculation: The camera determines the correct flash duration/power
4. Main flash: The strobe fires at the calculated power level
5. Quench: An IGBT (Insulated Gate Bipolar Transistor) cuts off the flash tube at the correct moment

The transition from film-era thyristors to digital-era IGBTs was critical because IGBTs switch faster, enabling the rapid preflash sequences required by digital cameras (^[23]).

Flash tube design significantly affects TTL performance. Linear tubes (used in INON Z-330, Sea & Sea YS-D3) fire in about 3-5 milliseconds, while circular tubes (used in Subtronic Pro-270, Seacam 60D/160D, Sea & Sea YS-250) take 10-20 milliseconds to complete their discharge (^[24]).

TTL vs Manual Flash

The TTL-versus-manual debate has been one of the most persistent discussions in the Wetpixel community, dating back to at least 2004 when Alex Mustard started the legendary “TTL Anonymous” thread with 114 replies (^[25]).

Arguments for TTL

• Speed with fast-moving subjects: Alex Mustard argued that TTL was essential for grab shots: “I don’t believe I would have got this shot shooting on manual. I needed TTL” — describing a lionfish shot taken by sticking the camera underneath the fish without looking through the viewfinder (^[26]).
• Macro convenience: David Haas found that Ikelite’s eTTL “worked very accurately” for fish and macro shooting, freeing him to compose while letting the camera control flash output (^[27]).
• Cold water practical advantages: Adam Hanlon noted that in cold water, “thick gloves, cold fingers and limited bottom times all mean that not having to adjust strobe output manually can be a good option for photographic productivity” (^[28]).
• Consistent exposure across apertures: James Wiseman tested Ikelite’s eTTL2 with a Canon 20D and found it reproduced exposures “within 1/2 stop of each other” across f-stops from f/2.8 to f/22 (^[29]).
• Digital converted some skeptics: Forum member timg reported in 2010: “I used to be a flat-earther: ‘who needs TTL strobes. Manual is good enough’. However having now had the Heinrichs Weikamp technology on my Subal/D300 system since June, there is NO WAY I would go back to manual” (^[30]).
• Continuous shooting capability: Nauticam USA highlighted that UW Technics converters unlocked continuous TTL shooting — “Previously, continuous firing was only available with a manual triggering system, but UW Technics unlocks this capability with optically synced flashes in TTL exposure mode” (^[31]).

Arguments for Manual

• Wide-angle unreliability: Alex Mustard identified a core problem: when the main subject does not fill the frame and is set against open water, TTL often overexposes the subject because “the TTL metering does not think it has given the subject enough light (because not enough has reflected back) and winds up the power” (^[32]). Forum user acroporas confirmed: “For wide angle eTTL is completely un-useable” — finding gross underexposure with an Ikelite eTTL housing and Sigma 15mm fisheye, while macro worked perfectly on the same dive (^[33]).
• RAW latitude makes it less necessary: James Wiseman countered this argument, noting that pushing RAW files carries penalties — boosting a D100 image by 2 stops effectively means shooting at ISO 800 with corresponding noise. “So in reality, you don’t actually have 2 stops in either direction to play with” (^[34]).
• Simplicity of a laminated card: Forum veteran manatee19 (Michel) described a practical manual approach: make bracketed test shots in a pool at distances from 1 to 5 feet, write down the results, laminate the card, and affix it to the housing with Velcro. He argued this 2x3-inch card was simpler than the “8 pages of TTL compensation values” one pro had documented (^[35]).
• The LCD as the best light meter: Eric Hanauer (ehanauer) commented on Mustard’s editorial: “The best light meter is the lcd display on the back of your camera. That instant feedback, along with the latitude of digi sensors on the down side, make ttl unnecessary” (^[36]).
• Professional consensus toward manual: By 2019, the debate had largely settled. Alex Mustard stated: “Strobe and flash trigger manufacturers seem obsessed with TTL systems, while none of the 100s of serious underwater photographers I dive with each year use it because it does not have the consistency of shooting in manual” (^[37]).
• One less thing to break: Forum member gudge cautioned that TTL “doesn’t mean you can leave your brain on the surface when using it” — noting that metering pattern selection, subject reflectivity, and scene composition all affect TTL accuracy (^[38]).

The Practical Consensus

By the 2010s, the community consensus was that TTL works best for macro with front lighting where the subject fills a significant portion of the frame, but is unreliable for wide-angle where large dark areas of open water confuse the metering system. Adam Hanlon found that TTL “coped well with side lighting, but seemed to struggle with back lighting” even for macro (^[39]). Ken Byrne on the forums recommended using spot metering with TTL for macro “so that the flash exposure is only exposing for the subject and not trying to light the background as well” (^[40]).

Alex Mustard also acknowledged a niche where TTL remained valuable: “One group who would greatly value TTL are tech divers who often require high-performance strobes with point and shoot simplicity on their challenging dives” (^[41]).

TTL Converter Systems

The underwater TTL converter market evolved from a fragmented landscape of incompatible solutions into a more standardized ecosystem, though no single universal system emerged.

Ikelite (2004-present)

Ikelite was the first company to offer digital TTL for underwater strobes, building conversion circuitry directly into their housing camera trays. Their eTTL circuit board for the Canon 300D (2004) translated the camera’s hot shoe signal to control DS-series strobes. David Haas tested it in the Galapagos: “By cracking Canon’s eTTL code first Ikelite housings offer a great tool to underwater shooters” (^[42]). Key features included back-mounted push buttons for flash compensation and mode switching.

Ikelite progressively expanded coverage: eTTL2 for Canon 20D (2005), i-TTL for Nikon (2005-2006), and Olympus/Panasonic support. The system required specific sync cords — the eTTL2 cord had a blue tape identifier, while standard TTL cords had yellow tape (^[43]). In 2007, Aquatica announced their housings would be available with the Ikelite ICS strobe bulkhead and hot shoe attachment, enabling use of Ikelite’s iTTL adapter for Nikon DSLRs (^[44]). In 2014, Ikelite and Aquatica formalized a partnership to offer Ikelite TTL circuitry in Aquatica housings, starting with the Canon 7D Mark II housing (^[45]).

In 2018, Ikelite released the DL1 DS Link Nikon TTL converter with Nikonos N5 connector for use with third-party housings ($375-$395), claiming their approach was “faster, more accurate, and more reliable than fiber optic TTL triggers” and required no batteries (^[46]). The RC1 TTL Receiver (2018) enabled fiber-optic TTL triggering of DS strobes with Olympus and Panasonic RC flash modes (^[47]). Canon and Panasonic/Olympus external converters (DL3, DL5) followed in 2020, priced at $375 (^[48]). Ikelite also shipped the DL4 DS Link Fujifilm TTL converter in 2019, extending their coverage to a fifth camera brand ($350-$395) (^[49]).

HeinrichsWeikamp / Matthias Heinrichs (2004-2011)

Matthias Heinrichs created the DA2 (Digital Adapter 2), the first popular slave TTL adapter for compact digital cameras. It offered three key innovations: a “recorded TTL” mode that prevented optical feedback by recording the internal flash signal and playing it back after the camera’s flash was extinguished; a user-settable gain factor to extend flash duration for larger strobes; and compatibility with many existing amphibious strobes (^[50]).

The DA2 cost less than a sync cord and worked with strobes like the Sea & Sea Z-220. In 2005, Heinrichs completed an eTTL2 converter with 2nd curtain sync support for Canon bodies (Rebel, D60, 10D, 20D) — a feature previously available only with Canon Speedlites (^[51]).

In February 2006, Aquatica began bundling the Heinrichs Weikamp iTTL converter in all their Nikon housings, with plans to add it to their Canon line. The converter was “a small unobtrusive adaptor” connecting inside the housing between the bulkhead and hot shoe adapter. Aquatica also offered to retrofit the board into older housings on request (^[52]).

Subtronic later integrated Heinrichs’ circuits into their Intellisync Cable for use with Pro160 and Pro270 strobes (^[53]).

However, the HeinrichsWeikamp system had camera-strobe timing limitations. By 2008, forum member BottomTime discovered that the converter would not work in i-TTL mode with a Nikon D300 and YS-110 strobes “due to the timing of the D300 being faster than the strobes (8ms vs 51ms)” (^[54]).

Sea & Sea TTL Converter

Sea & Sea offered their own TTL converter with compatibility charts published on their website listing supported camera/housing/strobe combinations. Erik Henchoz tested the Sea & Sea TTL Converter N with a Nikon D200, documenting results on his website (text in Italian). The converters worked with Sea & Sea’s YS-series strobes including the YS-110 and YS-120 (^[55]). Forum member Andrea reported “perfectly good results” with the Sea & Sea TTL converter, YS-120s, and a Nikon D200, noting “perfect exposures all the time and in all conditions” (^[56]).

Seacam Seaflash TTL

Seacam took a premium approach with the Seaflash 250 TTL (2007), a high-end strobe with built-in TTL circuitry. Andre Crone reviewed it, comparing its TTL to the Nikon SB-800 land flash (^[57]). Stephen Frink tested it at his Digital Master class in Key Largo and was impressed: “I have rarely seen a digital TTL test that truly worked underwater. This one did” (^[58]). Alex Mustard pushed back on Frink’s claim, noting he had “tested a wide variety of TTL systems underwater (housed land strobes, Ikelite converter, Heinrichs converter, INON s-TTL etc) and found that all work well” (^[59]).

UW Technics / Pavel Kolpakov (2016-present)

UW Technics, founded by Pavel Kolpakov, revolutionized the underwater TTL converter market starting in 2016 by producing internal and external converter boards compatible with virtually every major camera/housing/strobe combination. Their boards were the first on the market to incorporate optical TTL and electrical TTL in a single device, and introduced the concept of “Mixed TTL” — controlling one strobe optically and another electrically simultaneously (^[60]).

Key milestones:

• 2016 (BOOT Show): First product launched — Nikon-compatible TTL converter with 3 versions for different strobe types (Inon Z-240/Sea&Sea YS-D1/D2; Ikelite DS-161/DS-160; Sea&Sea YS-250). Battery life rated at 75,000 flashes from two CR2032 batteries (^[61])
• 2016-05: Nauticam USA began offering UW Technics converters as the NN-2/IS upgrade ($430). Field testing found it “the most well designed, feature rich, and consistently accurate converter we have tested” (^[62])
• 2017-01: External TTL converter announced with universal M14 screw mount, compatible with all Nikon cameras (^[63])
• 2017-03: External Optical TTL Converter reviewed by Adam Hanlon — fitted to a Seacam D500 housing with Inon Z-240 strobes ($495). Hanlon found it “accurate in measuring and applying the correct exposure in TTL mode” with 100% reliable firing (^[64])
• 2017-08: Canon TTL converter shipped for Nauticam, Sea & Sea, Nexus, Aquatica, Sealux, Seacam, Ikelite, and Meikon housings (^[65])
• 2018-12: TTL firmware for Subtronic strobes (^[66])
• 2019-02: Olympus TTL boards for Nauticam housings ($380), supporting Inon, Sea & Sea, Subtronic, and Ikelite strobes with 2 optical + 1 electrical TTL output (^[67])
• 2019-05: TTL converter for Sea&Sea MDX housings ($450) — Nikon and Canon versions with 2 optical + 2 electric outputs (^[68])
• 2019-07: Sony A7/A9 series boards ($450) and later Sony A6000 series ($450) (^[69], ^[70])
• 2020-02: Sony firmware update adding Retra Pro Flash TTL support with HSS (High-Speed Sync) up to 1/8000s (^[71])
• 2020-10: Full line of HSS TTL converters for Sony, Nikon, Canon, and Olympus — 38 new products released that year for housings from Nauticam, Hugyfot, Sea&Sea, Nexus, Isotta, Sealux, Aquatica, Seacam, Subal, Ikelite, Seafrogs, and Nimar (^[72])
• 2021-05: Canon EOS R5 TTL converter for Nauticam with HSS support — Kolpakov noted Canon had changed the R5’s TTL protocol from previous Canon cameras, requiring firmware updates (^[73])
• 2021-08: Nikon TTL board for Aquatica housings ($450) with HSS support for Retra strobes (^[74])
• 2022-11: Canon TTL board for Marelux housings (^[75])

UW Technics boards featured several innovations: no onboard battery requirement for some models (drawing microcurrent from the camera’s hot shoe pin); automatic on/off via camera command; per-strobe TTL profiles selectable via a 10-position rotary switch; firmware with profiles for Inon Z-330/Z-240, Sea & Sea YS-D1/YS-D2/YS-250, Ikelite DS-160/DS-161, Subtronic Pro-270/Pro-160, and Retra Pro; a “Controlled Manual Mode” allowing strobe power adjustment (1/64 to full) via camera controls; and full camera menu integration for switching between TTL/manual, 1st/2nd curtain sync, and flash exposure compensation (^[76], ^[77], ^[78]).

TRT-Electronics TURTLE (2016-present)

TRT-Electronics offered the TURTLE TTL converter series, initially for Olympus PT housings. The o-TURTLE (2017) was the “first chargeable TTL trigger for Olympus systems,” tested with OMD E-PL3, E-M5, E-M5 II, E-M10 II, E-M1, and E-M1 II. It featured a separate LED board for fiber optic triggering and front/rear curtain sync selection. Adam Hanlon explained in the comments that the o-TURTLE’s advantage over the built-in flash was power: “if the built in flash provides a pre-flash for TTL metering, it cannot then recycle fast enough to deliver a full power flash” (^[79]).

The TURTLE SMART (2019) was a universal, USB-programmable converter available for Nikon, Canon, Sony, Olympus, and Panasonic cameras at 329 euros. It featured a molded housing (36x26x15mm), replaceable hot shoe, and support for both fiber optic and electrical triggering. A smaller TURTLE SMART Mobie variant could be mounted anywhere inside smaller housings. The system was user-programmable via USB for different strobe configurations (^[80]).

High-Speed Sync (HSS)

A major development in the late 2010s was the introduction of High-Speed Sync capability to underwater photography. HSS allows flash operation at shutter speeds beyond the normal sync speed (typically 1/160-1/250s), up to 1/8000s. As Pavel Kolpakov explained, at high shutter speeds “the camera shutter window never opens fully but looks like a narrow moving part opened between two curtains. In this case, the flash lighting must occur with a long series of short flashes at a frequency of about 30 kHz while a partially open shutter window moves along the frame” (^[81]).

The development of HSS underwater was enabled by two concurrent innovations: Retra releasing HSS-capable underwater strobes, and UW Technics developing HSS-compatible TTL converter firmware. UW Technics released their first HSS firmware update for Sony converters in February 2020 (^[82]), then expanded to a complete line of HSS TTL converters across all major camera brands by late 2020 (^[83]).

Applications of HSS underwater include shooting near the surface under bright sunlight, creative shallow depth-of-field photography, and freezing fast-moving objects. Kolpakov noted that HSS “may also be helpful with cameras that offer relatively slow sync speeds” (^[84]).

Key Discussions

”TTL Anonymous” (2004)

The defining community discussion on the TTL-versus-manual question, started by Alex Mustard in the “Lights, Strobes, and Lighting Technique” forum. With 114 replies, it featured experienced photographers on both sides. Key contributors included James Wiseman (pro-TTL for macro, arguing digital RAW latitude was not free), manatee19 (Michel, anti-TTL, advocating laminated exposure cards), scorpio_fish, richorn, and Mike Veitch (^[85]).

”TTL… To Be or Not to Be?” (2008)

Forum member BottomTime documented the practical frustrations of the TTL converter landscape when transitioning from film to digital. Craig (forum) argued passionately that underwater strobe technology was “medievally dumb” compared to land flash systems and that IR-based protocols like Nikon CLS or Canon wireless could easily work through fiber and underwater. David Haas (dhaas) defended hardwired sync cords and noted that even land photographers often hardwire off-camera flashes (^[86]).

Nauticam D850 TTL Frustrations (2019)

Forum member Kelpfish reported persistent underexposure issues with the Nauticam D850 TTL converter, finding “90 percent are way under exposed” for simple macro subjects. The thread highlighted the gap between TTL converter claims and real-world underwater performance, with chrisross offering diagnostic advice about the chain of components (camera metering, TTL converter synchronization, fiber optic cable quality, strobe sensitivity) that must all function correctly. Veteran davehicks responded: “As it turns out TTL is not all that. At the end of the day after using Ikelite TTL for years and then going manual for many more, I would not bother with TTL if I had it to do again” (^[87]).

Wetpixel Live: TTL and Ambient Light (2020)

Adam Hanlon and Alex Mustard discussed using TTL with fast-moving subjects on their Wetpixel Live YouTube channel, acknowledging TTL’s value for action shots while noting its limitations (^[88]). The foundational TTL-vs-manual question was also the subject of the series’ most popular episode (Ep 6, 10,654 views), while a separate episode (Ep 35) addressed high-speed synchronization techniques (^[89], ^[90]).

Notable Practitioners

• Alex Mustard — Tested many TTL systems extensively. While he documented TTL’s value for grab shots, he ultimately advocated manual control for serious work, writing the influential “Trouble with TTL” editorial in 2006 and maintaining his anti-TTL stance through his 2019 ONEUW review (^[91], ^[92], ^[93])
• James Wiseman — Conducted systematic TTL testing for Wetpixel, including the first eTTL2 and INON S-TTL reviews. Advocated intelligently for TTL’s benefits while acknowledging its limitations (^[94], ^[95])
• Pavel Kolpakov — Founder of UW Technics, described by Wetpixel as “an acknowledged expert in the design and manufacture of underwater lighting control systems.” His company decoded TTL protocols for all major camera brands and designed converter boards used across the industry (^[96])
• David Haas — Ikelite dealer and photographer who wrote the first in-depth eTTL converter review based on shooting in the Galapagos (^[97])
• Julian Scheunemann — Conducted detailed comparative tests of INON D-2000 S-TTL vs DA2+Z-220 slave TTL, prompting INON Japan’s official technical response (^[98], ^[99])
• Matthias Heinrichs — Created the DA2 (Digital Adapter 2), the first popular slave TTL solution for compact digicams, later developing eTTL2 converters with 2nd curtain sync. His circuits were adopted by both Aquatica and Subtronic (^[100], ^[101], ^[102])
• Stephen Frink — Tested the Seacam Seaflash 250 TTL at his Digital Master class and declared it one of the rare digital TTL systems that “truly worked underwater.” Also documented the D2X hotshoe syndrome and fix (^[103], ^[104])
• Adam Hanlon — Reviewed the UW Technics External Optical TTL Converter, co-hosted Wetpixel Live episodes on TTL and flash firing, and used UW Technics converters for Red Sea strobe testing (^[105], ^[106])

Timeline

• 1984: TTL strobe control introduced with the Nikonos V, becoming the standard for film-era underwater photography (^[107])
• 2002-06: scorpio_fish raises the digital TTL compatibility crisis on Wetpixel forums — existing housings cannot provide TTL with digital SLR strobes (^[108])
• 2004-01: Aquatica announces they have cracked the E-TTL code for Canon 300D Digital Rebel (^[109])
• 2004-01: Ikelite begins beta testing Olympus TTL circuitry for the 5050/5060 (^[110])
• 2004-03: Eric Cheng reports on Aquatica’s E-TTL to TTL bridge at Boston Sea Rovers (^[111])
• 2004-08: Alex Mustard starts the “TTL Anonymous” thread — 114 replies debating TTL vs manual (^[112])
• 2004-09: Ikelite announces eTTL bridge for Canon 300D with DS-50 and DS-125 SubStrobes (^[113])
• 2004-09: Subtronic announces mini EOS 300D ETTL strobe (^[114])
• 2004-11: David Haas reviews Ikelite 300D eTTL housing from the Galapagos (^[115])
• 2005-02: James Wiseman tests Ikelite eTTL2 with Canon 20D (^[116])
• 2005-02: Julian Scheunemann publishes comparative slave TTL test: INON D-2000 vs DA2+Z-220 (^[117])
• 2005-03: INON publishes official S-TTL technical explanation with waveform analysis (^[118])
• 2005-03: James Wiseman reviews INON D-2000 S-TTL strobe for Wetpixel (^[119])
• 2005-06: Matthias Heinrichs completes eTTL2 converter with 2nd curtain sync for Canon bodies (^[120])
• 2005-11: Stephen Frink documents D2X hotshoe syndrome and Seacam’s pin-removal fix (^[121])
• 2006-01: Alex Mustard publishes “The Trouble with TTL” editorial on Wetpixel (^[122])
• 2006-02: Aquatica bundles HeinrichsWeikamp iTTL converter in all Nikon housings (^[123])
• 2007-01: Sea & Sea TTL Converter compatibility chart discussion — Erik Henchoz tests with Nikon D200 (^[124])
• 2007-04: Aquatica announces Ikelite ICS strobe bulkhead compatibility for iTTL (^[125])
• 2007-12: Andre Crone reviews Seacam 250 TTL strobe (^[126])
• 2008-03: Sea & Sea announces YS-17 TTL slave strobe for compact cameras ($349) (^[127])
• 2008-07: Stephen Frink’s Seacam Seaflash 250 TTL test sparks debate about which TTL systems “truly work” (^[128])
• 2011-11: Subtronic releases TTL convertor cable integrating Heinrichs Weikamp circuit (^[129])
• 2014-12: Ikelite and Aquatica partner to offer Ikelite TTL circuitry in Aquatica housings (^[130])
• 2016-02: UW Technics launches first TTL converter at BOOT Show — world’s first combined optical + electrical TTL board (^[131])
• 2016-05: Nauticam USA offers UW Technics TTL converter as NN-2/IS upgrade ($430) (^[132])
• 2017-01: UW Technics announces external TTL converter with universal M14 mount (^[133])
• 2017-03: Adam Hanlon reviews UW Technics External Optical TTL Converter (^[134])
• 2017-08: UW Technics ships Canon TTL converters across 8+ housing brands (^[135])
• 2017-11: TRT-Electronics ships o-TURTLE TTL trigger for Olympus (^[136])
• 2018-02: Adam Hanlon tests Inon Z330, Retra Flash, and Symbiosis SS2 strobes with UW Technics TTL converter in the Red Sea (^[137])
• 2018-07: Ikelite announces RC1 TTL receiver for Olympus/Panasonic fiber-optic triggering (^[138])
• 2018-08: Ikelite announces DL1 DS Link Nikon TTL converters ($375-$395) for third-party housings (^[139])
• 2018-12: UW Technics releases TTL firmware for Subtronic strobes (^[140])
• 2019-02: UW Technics ships Olympus TTL converter boards for Nauticam ($380) (^[141])
• 2019-02: TRT-Electronics ships TURTLE SMART universal TTL converter (329 euros) (^[142])
• 2019-04: Ikelite ships DL4 Fujifilm TTL converters ($350-$395) (^[143])
• 2019-05: UW Technics ships TTL converter for Sea&Sea MDX housings ($450) (^[144])
• 2019-07: UW Technics launches Sony mirrorless TTL boards for Nauticam ($450) (^[145])
• 2019-10: UW Technics ships Sony A6000 series TTL converter ($450) (^[146])
• 2020-02: UW Technics Sony firmware adds Retra Pro Flash TTL with HSS to 1/8000s (^[147])
• 2020-02: Ikelite ships Canon and Panasonic/Olympus TTL converters (DL3, DL5, $375) (^[148])
• 2020-07: Wetpixel Live: TTL and shooting with ambient light (^[149])
• 2020-10: UW Technics releases full line of HSS TTL converters — 38 new products across all major brands and housing manufacturers (^[150])
• 2021-05: UW Technics ships Canon EOS R5 TTL converter with HSS for Nauticam (^[151])
• 2021-08: UW Technics ships Nikon TTL board for Aquatica housings ($450) with HSS (^[152])
• 2021-09: Pavel Kolpakov publishes “Fundamentals of TTL Strobe Control” on Wetpixel (^[153])
• 2022-11: UW Technics ships Canon TTL board for Marelux housings (^[154])

References

Wetpixel Live