Adventurer

Thank you, but can you confirm that you are using a Nikonos III Version 15mm lens in the same adapter as the Nikonos V 15mm ? I am in doubt that this is possible. I had to put the project aside in frustration, for the following reasons: The Nikon Z Mount has a Flange Distance of 16mm, the Canon RF Mount has a Flange Distance of 20mm, and the Sony E Mount has a Flange Distance of 18mm. Sony E Mount = 18 mm Nikon Z Mount = 16 mm ( -2mm ) Canon RF Mount = 20 mm ( +2 mm ) A Nauticam Full Frame Nikonos Adapter exists for Sony N100 Nauticam Sony (N100) Flange Distance = 28 mm * Marelux Canon Flange Distance = 51 mm ( + 23 mm ) * Nauticam Sony N100 flange distance has strangely been reported with 3 different measurements (by owners) in this forum: 28 mm, 27mm and 26mm . Hence, for getting a Sony N100 Nikonos adapter to work inside a Marelux Canon housing it would need to move 25mm, or even 28mm inwards, depending what customer measurement you trust. This seems nearly impossible with the knobs on the side, as the Nikonos II 15mm lens has a diameter to aperture + focus knob of 132 mm. Furthermore my flange distance Google research / Wikipedia Germany claims that: Wiki Nikonos Flange = 28.00 mm vs. Google AI pulls of = 46.50 mm ..but I measured the following flange on my Nikonos III camera * * I put the camera in B (bulb mode) and pressed the shutter to really reach down to film plane behind the shutter with a calliper lower silver contact: 32 mm upper silver lip: 39 mm ( + 7 mm ) not matching any of the two web-researched infos above. Can anybody confirm that the Nikonos II cameras flange distance is different from Nikonos V series ?

No, you should definitely not accept that and keep in mind what Alex said: I think several of us here, especially Alex and Matthew have experienced more than 2K or high definition in their digital underwater photos, even when taking pictures behind a dome port. It highly depends on your prudeness with port positioning and and dome size selection. .. maybe you can pass him a visit at look at the humongous amount of Nikonos glass he is hoarding 🤪 ( https://achtel.com/nikonos-lenses/ ) which makes me pack my bags and want to move to Australia, instantly! *Alex and Matthew own the "holy grail" (adapted Nikonos RS13 Fisheye) and a (hopefully well positioned) 8-15 fisheyes behind domes and may comment / judge their personal perceived resolution advantage. Alex on top may also compare it to his Ivanoff Zeiss 20mm experience and the Nikonos V 15mm lens on a full frame.

Well it turns out, that this is very unlikely to be a problem when searching the sharpest knives (lenses) for underwater imaging. As @Chris Ross 's linked blog post and @Alex_Mustard 's Admiral Achtel's thoughs brought up the optical Nyquist limit I dove a little deeper into the physics and technical aspects behind it. For Chris's concern,... if we look at MTF50 charts only, not MTF10/MTF20, the results are indeed quite comparable with a potential offset between 0% and -15%. We can keep this in the corner of our head. IMPORTANT: the Nyquist limit is raging against Diffraction Airy disc limit. Diffraction kicks in earlier then Nyquist limit, forcing you to use more conservative F-Stops. But it is very handy to know what might define the true optical theoretical ceiling with various full frame cameras in 2026. For example my Canon R6 II will most likely not resolve lenses that excel beyond 83.33 lp/mm - and your Canon R5 II or Sony A1 II will most likely not suck out much more than that, as you will kill IQ earlier with diffraction. I compiled the following handy table for your reference:

Unfortunately we are drifting away in this thread with a lot of speculation, hairsplitting and nothing new brought to the table by some contributors. This was not what I wanted in the topic opener. I want lens pitches ( „potentials“ ) which we can explore and test AND quantifiable (lp/mm and LW/PH) to get an idea where they possibly stand. These of course have to be ranked in separate lists for each camera brand bayonet and are not cross comparable. It‘s also problematic if you compare testing website source A with website B or have to compare underwater or topside values. But you have to start somewhere to get a vague idea on what’s possible. Also I think it‘s important to relate to something you know. Many of us have the EF 8-15 (or an RF100) and can therefore relate to how pixelpeeping a 54 lp/mm (or 86,5 lp/mm) candidate looks like.

Thanks for this Link! Surprisingly, this puts the “legendary” Nikonos V / UW-Nikkor 15mm at about 51.9 lp/mm, i.e. below the RF 100mm and closer to EF 8–15mm land performance — and here’s why: 1) The test is not full frame (crop factor first, and it also explains the reduced underwater FOV) The Wetpixel/Achtel measurements were done on a RED EPIC MYSTERIUM-X (Super-35) recorded in 5K 2:1 (5120×2560). In that mode the active imaging area is roughly 27.65 × 13.83 mm, which is about a 1.40× diagonal crop compared to 36×24 mm full frame. That crop factor directly explains why the underwater diagonal FOV quoted for the Nikonos 15mm looks “reduced”: the UW-Nikkor 15mm is specified around ~94° diagonal underwater, and applying ~1.40× crop gives roughly ~75°, consistent with the ~74° figure discussed in this context. So this is primarily a format/crop effect, not the lens “getting narrower” underwater. 2) Why an “edge” Imatest ROI on this setup is not a full-frame corner If Imatest samples an edge/ROI near the edge of the RED frame, that location maps to about 1 / 1.40 ≈ 0.71 of the full-frame image radius. In other words: it corresponds to mid-to-outer field on full frame, not an extreme 36×24 corner. So the Imatest result should not be interpreted as “full-frame corner performance.” 3) The lp/mm number is a derived value (LW/PH → lp/mm conversion) Imatest reports MTF50 in LW/PH (line widths per picture height). To convert to lp/mm on the sensor plane: lp/mm = (LW/PH) / (2 × picture height in mm) For RED 5K 2:1, picture height is ~13.83 mm. With the reported MTF50 ≈ 1434 LW/PH: lp/mm = 1434 / (2 × 13.83) = 1434 / 27.66 ≈ 51.9 lp/mm Bottom line: the widely quoted ~51.9 lp/mm is a converted sensor-plane MTF50 number on a cropped Super-35 capture, and the sampled field position is closer to mid/outer field than a true full-frame corner. As the values I initially posted for comparison were also center / near center based performance values in lp/mm we can use this for comparison. We should however honor the high open aperture resolution performance of the Nikonos V 15mm while keeping the dismal flexibility and manual focussing required underwater in mind when judging the practicability.

If you look at the entrance pupil position, of the Canon EF 8-15 everybody in this forum who used and tested the small Nauticam and Marelux (approx 140 diameter) dome is suffering from a mis-positioned lens. Both these domes are not full spheres. They are missing a tiny bit and the ball is not exactly cut in half. Due to that it‘s recommended to shoot them at minimum F16 or smaller aperture values. If you want to max out the IQ and archive „superposition“ you have to die the death of vignetting and combine it with a 2.0x TC and in most cases you will also have to remove the sunshade of the dome underwater and use it from approx 18mm to 20mm focal length onwards. With my MARELUX and small dome this wil require 85mm of extension rings. Vignetting disappears from 18mm onwards.

Welcome, Tia — two quick thoughts that may help: There’s a must-read thread on corner sharpness with the Canon 8–15 fisheye. The author questions the Nauticam port chart and also ran extensive Nauticam port tests. It includes a simple “at home” position test you can do to confirm whether the lens is sitting at the correct position in the dome: https://waterpixels.net/forums/topic/1438-testing-nauticam-n120-port-extension-for-140mm-and-180mm-domes-with-wide-angle-lenses/ Even if everything is set up correctly, you can still run into depth-of-field limitations underwater (similar to what you’re seeing on land). Your sample image might be a good example of that. Former forum member Interceptor121 has a very good write-up on this, and he repeatedly notes that placing your focus point closer to the corners of the frame can help improve corner sharpness: https://interceptor121.com/2023/03/18/canon-8-15mm-with-kenko-1-4-teleconverter/

Nope - or did you mean it the other way round and this was a typo? I guess you fell in the common trap that prices in the EU are only allowed to be advertised incl. VAT, while online advertised prices in the USA excl. VAT.

Definitely buy yourself the EF-RF Adapter from Canon. There is so much you want to transfer into your new system! For example the Canon EF8-15 a very important valuable lens. You may even easily cross over from Nauticam to Marelux, as they offer Nauticam port adapters.

„The dial“ is also available on your Marelux housing. It will be your Aperture, Shutter Speed or ISO dial, depending on your R6M2 configuration. The arrow keys do the same thing as they do, when you push the touchpad of your camera when not installed in the housing 😉

Yes, indeed - glad you mention it, Matthew. However we all rely on personal impression reports like yours and Alex‘s. Unfortunately there has been no quantified lab test with this lens which measures (underwater) in lp/mm. So we do not know how much we are potentially missing out 😅. I do believe you guys, though! To give everyone a good, relatable reference: the often-discussed Canon RF 100mm f/2.8L Macro manages to reach up to 86.5 lp/mm at f/4 in the image center. (source: digitalkamera.de lab tests). So unless you use focus stacking it‘s not very realistic to archive under practical underwater application. @F16 it bends down to 61,8 lp/mm in the center; and with F22 it’s down to 49,5 lp/mm. So due to macro practical depth of field requirements you might have experienced that lens just similar sharp or even less sharp than your EF8-15. I recall that @MatthewSullivan was praising the RF100 macro for its sharpness in the underwater photography show on YT and also happens to shoot and own the adapted RS13 fisheye ( „the holy grail“ ). So having the numbers rankings, he could maybe make a well informed expert guess on the RS13‘s lp/mm sharpness value? RS13 adapted = ???? lp/mm RF100 @ F4 = 86,5 lp/mm EF 8-15 Fisheye = 54 lp/mm RF 24-50 @ 24mm + F11 = center 52,8 lp/mm edges 41,2 lp/mm @Muellema to answer your question: all lenses that can be adapted / used with full frame mirrorless; or better: that make sense of being used to max out IQ on your full frame mirrorless system. Sharp RAW output is measurable in lp/mm or lw/ph (resolution).

Hi Tim, I hope we do not drift away from my initial aim with this post. I think I pretty much highlighted the practicability part above and can tell you (by experience) that the Tokina 10-17 pitched a great concept but is IQ wise totally inferior to the Canon EF 8-15 F4 L - for the sake of trying to nail the cream of the crop here, I would also appreciate if we can stick to FULL FRAME MIRRORLESS systems and leave APS-C, M43 and compact out of the topic.

I’d like to throw out a structured thought experiment and get input from others who are chasing maximum optical quality underwater. The idea is a bottleneck search: identifying which part of the optical chain ultimately caps achievable sharpness, and how modern lenses may have shifted that ceiling. If we ignore water quality for a moment, I think underwater image quality can largely be reduced to three primary, controllable factors: Camera & Sensor Pixel pitch and diffraction limits define the aperture range where the sensor can still resolve real detail. Higher-resolution sensors tend to hit diffraction earlier, which already caps usable sharpness. The Lens (Topside Performance) Every lens has a measurable resolution ceiling, typically expressed in line pairs per millimeter (lp/mm) under controlled lab conditions. This is the absolute upper bound of what the system can ever deliver. Dome Port or Underwater Corrective Optic (WACP, FCP, etc.) These elements can preserve or destroy resolution, but they cannot exceed the lens’s native resolving power. They are enablers—not multipliers. My working assumption is therefore: No underwater optic or dome can ever push image quality beyond what the lens–sensor combination can already resolve topside. For anyone interested in comparing topside lens performance in a more objective way, I’ve found two resources particularly helpful. The ISO 12233 sample crop tool at https://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=1624 allows direct visual comparison of resolving power across lenses and sensors, while https://opticallimits.com/the-list/ provides a concise overview of laboratory-measured resolution data across many modern and legacy lenses. A Reference Point: Canon EF 8–15mm Fisheye In underwater photography circles, the Canon EF 8–15mm f/4L Fisheye has long been regarded as one of the sharpest and most reliable underwater lenses ever made. That reputation is not anecdotal—it is backed by lab data. From LensTip’s resolution test (more than a decade old): “The performance you can see on the graph can be only described by one word: revelation. At shorter focal lengths the lens, even wide open, reaches a level of 50 lp/mm or higher and by f/5.6 it gets to record-breaking values of 53–54 lp/mm.” ( source https://www.lenstip.com/311.4-Lens_review-Canon_EF_8-15_mm_f_4_L_Fisheye_USM_Image_resolution.htm ) At the time, this effectively outperformed almost every other EF lens tested. In underwater use, the lens also benefits from extremely close focusing, which reduces water column and often compensates for other optical weaknesses. This is arguably a fourth, indirect factor: minimizing the amount of water between lens and subject. The Shift with Modern RF Lenses Here is where things get interesting. If we look at modern Canon RF lenses, even non-L designs now meet or exceed resolution levels that were once considered exceptional. For example, laboratory testing from digitalkamera.de reports the following for a very modest kit zoom: Canon RF 24–50mm F4.5–6.3 IS STM (tested on a 24 MP EOS R8): “The lens reaches a maximum resolution of 57 line pairs per millimeter (lp/mm) in the image center and 49 lp/mm at the image edge at a focal length of 35 mm.” In other words: A small, inexpensive, non-L RF zoom already exceeds the peak resolution of the legendary EF 8–15mm fisheye, at least in topside lab conditions. This strongly suggests that modern mirrorless lens design has raised the baseline for optical sharpness, and that many assumptions carried over from the EF era may no longer hold. The Exception—and the Real Question The EF 8–15mm remains special not just because of resolution, but because it combines: Very high lp/mm performance Extreme close-focus capability Excellent compatibility with small domes Reduced water column in real underwater scenarios That combination makes it a rare exception where practical underwater sharpness can rival or exceed newer lenses that are sharper on paper but harder to deploy underwater. This leads me to the real questions I’d like to discuss: What is the sharpest lens (in lp/mm terms) available today for your system—Canon RF, Canon EF, Nikon Z, Sony E? Which of these “topside gold nuggets” can realistically be used underwater with domes or corrective optics like WACP/FCP? Are we still overvaluing classic underwater lenses, while underestimating what modern mirrorless optics could deliver if paired with the right underwater solutions? I’m very curious to hear which lenses you think currently define the true optical ceiling for underwater photography in your system—and whether anyone has successfully translated that topside sharpness into real underwater results.

Exactly my experience; this is why I do not like float belts. Two -650g INON Mega Float Arm M is my base configuration for the Backscatter HF-1. I combine them with stick arms each to be able to fold them in nicely in 45 degrees left and right. This will usually give you your base trim. A third float on a ball in the middle if needed. I recommend to test all in a bathtub at home before embarking on a trip.

These INON Float Arms serve me for several years now: https://www.hydronalin.eu/inon-mega-float-arm-s-mit-390-gramm-auftrieb_2058 They come in various shapes. Very lightweight, durable and have two M5 threads on which you can connect accessories such as LensHolders, Actioncams etc.