Hi, I am looking for knowledge exchange and more experimental tipps running an underwater corrector port Ivanoff style that I have been testing & shooting since yesterday on my Marelux MX-R6II.

Mine was not made by the famous Carl Zeiss, though. I think it was designed by fathom optics in the USA around the year 2000 for video shooters.

I was hoping to shoot a flexible 24-70mm or 28-70mm behind it, but failed. MFD of the lens utilized behind it seems crucial as with dome ports. The Canon RF 28-70 and 24-70 options have really bad MFD, even worse than the RF 24-50.

The Canon RF 15-30mm IS STM seems run awesome behind the optic. It is severly larger than the Carl Zeiss underwater corrector port that @Alex_Mustard has used before.

The cheap Canon RF24-50mm which is said to run nicely behind a WWL-1C(?) has turned into a complete failure behind that water contact optic. It just cannot focus once you zoom in and it fails to focus on land through the optic. I think it‘s due to the bad MFD of that lens.

However I have some flexibility concerning the amount of extension rings I can put in between and I would like to nail the best focal point possible behind the curved inner sphere.

If some of you have links to scientific papers or schematic drawings of Ivanoff style optics I would be very thankful if you could share them with me.

Edited July 8, 2025Jul 8 by Adventurer
added some images of the construct

Interesting, never heard of them before now! My first thought is that if it's for video cameras from around 2000 time frame it would be designed around relatively small imaging sensors?

I assumed you have asked Google, I had a look and found a Wetpixel article from 2003 (mostly buzz and fluff, but did mention a few cameras it might work with) it mentions that fathom port working with the 1/3"sensor on the VX2000 (6.0 mm diagonal size) Also found that Fathom imaging is still a going concern offering UW correction lenses so should be contactable.

My second thought is that if you know what lenses it was designed for you could take look them up to get an idea of what sort of specs they have and match them up with modern lenses you might be able to use. For example the VX-2000 mentioned on the WP page has a min focus distance of 300mm for the factory lens - though the article does talk about using a custom Gates lens as well. Do you know the model name for the fathom lens?

I have the Carl Zeiss designed Ivanoff, which I used extensively with a 20mm lens on Nikon SLR (my friend Peter Ladell converted the port fitting). I have not converted it for my Sony because the Nikonos 15mm has almost identical performance, but I am sure I will experiment with it again in the future.

I used it to take quite a lot of photos, such as this well-known one:

Wildlife Photographer of the Year

Rig diver | Wildlife Photographer of the Year | Natural...

Diving beneath the oil rig, Alex had to anticipate when the cormorants would burst through the fish shoal. The birds hide behind the legs of the rig after they plunge into the dark waters, gaining...

This is another:

The Zeiss corrector has two lenses - the port and then a second corrector lens that goes on the front of the camera lens. I tested it with and without this internal corrector lens - and without it the Ivanoff was no better than a dome, but with it, it rivalled a water corrected lens like the Nikonos. At the time I tested one other Medium format Ivanoff corrector port (from a Mamiya 6x7 housing) and this was similarly "no better than a dome" - and it did not have an internal corrective lens.

Lots of Ivanoff style ports were made for video cameras in the 90s. They weren't amazing optically, but worked well enough for the low-res video of the day. They were smaller and more robust than domes and I feel worked well with the physically small lenses on video cameras.

A frustration with the Zeiss system was that the internal corrective lens was quite small in diameter (made for the Hasselblad SWC) and this limited the lenses I could use with the port to those that had a physically small front element. I tried a number of lenses, but none worked as well as a Nikon 20mm.

I would put more effort into reviving my port - but for now the Nikonos 15mm is basically doing the same job for me. Yes, I don't have AF, but that is less of an issue than you might think. And it is smaller and lighter than the Ivanoff.

I'll watch your tests with interest. Because I quite quickly lucked into a system that worked really well, I felt I never tasted variables that thoroughly. Once I had the right port extension and found that the internal lenses worked great with the 20mm, I just got out there and used it. When ever I varied things the results deteriorated quickly, which also put me off doing more tests.

Alex

11 hours ago, Chris Ross said:

My first thought is that if it's for video cameras from around 2000 time frame it would be designed around relatively small imaging sensors?

Well I seem to be lucky as the Ivanoff style lens on my desk is humongous.

It was given a lot of great glas, partially due to the fact that the cam it was designed for played in the broadcast league 20 years ago ( 2005 ).

I have added more extension rings and moved the optics much more forward with promising results.

I might be really lucky as the camera had a 3 CCD design https://en.wikipedia.org/wiki/Three-CCD_camera

If you look at the construction each sensor was very small but the prism (equivalent to what you would call sensor plane today or the film slide in Nikonos days) is much larger, as it was a physical construct splitting the light up into the 3 tiny CCDs. I think therefore the optical engineers had to give the optics more space. Even though the camera was recording in 16:9 format I do not seem to suffer from that. The IQ seems to scale-up nicely in the whole 3:2 field. The only constraint seems to be the very long sunshade (which cannot be removed) at the top and bottom. However I was able to use this as a reference point for the focal length it was rendered for. Just zoom in underwater until you cannot see the sunshade anymore ;-)

With the Canon RF 15-30 IS STM:
It seems to run fine, starting at 25mm focal length.
However I suppose it was designed for 28mm or even 32mm.

The broadcast HD camera it was designed for had a large filter thread of 72mm which might allow me to tweak it with lenses that have physically small front element, such as Canon's RF 16mm (31mm front glas).

I might also give my Samyang RF AF 14mm f2.8 a try with it, which has a physically large front glas element of 72mm.

I'll keep you posted on my progress and findings and would love to see more images taken with the Zeiss, Alex.

By the way, this is the old initial patent file of A. Ivanoff Patent No 2730014 dated 1956:
https://www.freepatentsonline.net/2730014.html
(the direct download to the PDF goes via this link)

An a very interesting old (1967) paper about designing uw lenses, citing Ivanoff:
https://www.asprs.org/wp-content/uploads/pers/1967journal/aug/PERS(33)8-925.pdf

Edited July 9, 2025Jul 9 by Adventurer
added link for direkt download PDF at amazonaws

Here is an update,…

I ruled out the

Canon RF16

Samyang RF 14mm

and organized myself an

Canon RF 24-50mm STM

Canon RF 28mm STM

Canon RF 24-105mm STM

The 24-105 is the hot item here.

Mainly due to it‘s minimum focusing distance on the 24mm end.

Depending on the extension rings used, I can decide if I want to use it in a range of

• 32-85mm zoom range

• 24-72mm zoom range

I have to take it out to the water and give it a walk in the field for real live shooting.

Furthermore the 28MM prime ditches flexibility but seems to be dent sharp at F4 mixed with the water contact optic.

I would like to give everybody an update about my time and shooting experience with the above optic.

Overall resumé : I am in deep love!

The setup I am shooting with the Canon RF24-105 STM is a dream combination, filling the flexibility gap between my 8-15 Fisheye and the 100mm macro lens.

Beeing able to shoot substantially wide dent Sharp reef scenes and fish portraits on a single dive with a full frame mirrorless system is amazing.

However I would like to put some terms straight that may have been coined wrongly by the Keyword „Ivanoff Optik“ inspired by our dear Dr. Alex Mustard and who got me started researching and exploring this road.

Alex was in fact shooting a Ivanoff-Rebikoff optic with 20mm fixed focal lengths, which is internet keyword wise sometimes just referred to as Ivanoff-corrector Port oder Ivanoff-Optic, leaving out the credits for Mr. Dimitri Rebikoff.

During diving deeper into the topic,

I found that I am actually shooting a Rebikoff optic, which goes without the correcting inner collection lens presented in their later introduced Ivanoff-Rebikoff design (sometimes referenced as IR design).

All three approaches have their caviats. And as you have just read 3 instead of two, yes

• Rebikoff fronts glas uw correctors

• Ivanoff-Rebikoff corrector ports

• Dome ports

..share some commonalities in what’s possible concerning their optical limits.

Most importantly the entrance pupil position problem cannot be thrown overboard with any of the above design.

Furthermore they also benefit all from the same factors defined by the hosted dry air lens inside of them.

The Ivanoff-Rebikoff design and Domeport have in common that they will extremely benefit from lenses that do not very much move the entrance pupil, most commonly found with fixed focal length. This explains also why Alex‘s IR-corrector port works splendid with a certain 20mm lens and created dismal results when trying to apply „the cure“ to other lenses.

While everyone of you can easily work on optimal dome port position, you will very much likely fail in computing and manufacturing the exact Ivanoff Element for an Rebikoff-Ivanoff underwater corrector port and your lens; for the sake of beeing extremely costly.

My suggestion for everyone is, if you are into exploring paths offside your dome port try to find large 2nd hand Rebikoff underwater corrector ports and start approximations with lenses from your camera brand, Nikon Z, Canon RF or Sony E-Mount. The latest UD elements and other 21st century master technology may help you to luck into a system that outperforms other optical underwater solutions you dived.

For some extended reading about Rebikoff and Ivanoff .. their work and later collaboration I recommend these articles:

https://blueexplorermag.com/2023/10/28/illuminate-the-abyss-the-innovative-inventions-of-dimitri-rebikoff-coloured-the-underwater-world/

https://spie.org/news/photonics-focus/julyaugust-2023/dimitri-rebikoff-pioneer-of-underwater-photography

https://frogmanmuseum.free.fr/html/camerasandvideosrebikoffen.htm

https://www.collection-appareils.fr/x/html/camera-5074-Alpa_U-Phot.html

I see you're enthusiastic about this lens and that now even Seacam has brought the project up to date again.

The result is a rectilinear image, right?

Could you share the results you've obtained with yours?

Thank you in advance

I second Davide! I am curious about:

1. Rebikoff fronts glas uw correctors

2. Ivanoff-Rebikoff corrector ports

What is the difference and please provide citations? I ask because Rebikoff used inconsistent nomenclature in his books. I have his 1955 and 1965 books published in the US. They are very simmilar even using some of the same pix. See attachment. From what I know Ivanoff wrote the patent and Rebikoff actually built them. Apparently early in France and then in the US.

16 hours ago, Tom Kline said:

I ask because Rebikoff used inconsistent nomenclature in his books.

Thank you @Tom Kline for this find. I have just ordered a copy of that old book and am exited. According to my research there are clear indications that Dimitri Rebikoff had already been working on water-contact corrective lenses before the joint “Ivanoff-Rebikoff” optics project. The classic Ivanoff-Rebikoff lens is more of a later, joint highlight—not the beginning of his work in optics.

From what I know until now I cannot agree to your assumption that "Ivanoff wrote the patent and Rebikoff was the builder". Dimitri Rebikoff (1921–1997) started working on several underwater innovations in the early 1950s. One of them was Poodle ROV (approx. 1953–1954)

Reports on the first civilian ROV, the “Poodle,” describe how Rebikoff

• placed a camera in a pressure-resistant housing and

• mounted a “water-corrected” or “water-correcting lens” in front of it

in order to film Mediterranean wrecks at a depth of 700 ft.

This is an explicit water-contact correction lens – decades before Nikon/Nauticam etc. took up something similar again, and long before he started his joint works with Ivanoff. An optics blog about “Air Lenses” writes that the classic Ivanoff-Rebikoff corrector system was “devised in 1960.” Modern photogrammetric works cite this optics as the Ivanoff-Rebikoff corrector, with references such as “Ivanoff and Cherney 1960, Rebikoff 1968.” This suggests that the first formal description of the optics appeared in scientific literature around 1960.

Your later revision of the book (assuming the right book "saying System Ivanoff" is from 1965) would fit along well in this research and explain the photo caption inconsistency you found.

It looks to me, that in both versions of the book the two illustrated lenses are not ment to be working on the same camera rig at the same time. They are two different Rebikov optics, without the contribution element that his collaboration with Ivanoff brought to life.

The first photo I have found of a similar system that is illustrated on page 31 in your left book (as above written, I assume that is the older one) was used in his underwater scootering camera rig which you can still find in the diving hall of fame online today:

source: SCUBA Diving Hall of Fame

17 hours ago, Tom Kline said:

I second Davide! I am curious about:

1. Rebikoff fronts glas uw correctors

2. Ivanoff-Rebikoff corrector ports

What is the difference and please provide citations?

Maybe @Alex_Mustard can drop in an iphone picture of his glas element that is attached to his 20mm lens inside the housing and the front port element when the housing is dismantled.

The two components are not hardwired to each other.

The Rebikoff Element or Rebikoff optic is the part that touches the water and also seals the housing. It's not a simple flat port. The part that I named "Ivanoff" Element in the Ivanoff-Rebikoff System is what the joint venture of the two inventor brought new to the table in the early / mid 1960s.

Here is a photo of my port and internal lens (not attached to housing or lens):

When searching my phone for the word Zeiss (to find the picture) this one came up of another one of the shots from it in print:

And here are a couple more from my website that I didn’t share previously:

In the UK, the older guys who used these in the 1960s and 1970s always called them Ivanoffs. I suspect that this was because they didn’t like Rebikoff personally, probably because of his commercialisation of the idea! That’s why I always call it an Ivanoff or simply a Corrector Port - as I was taught about it from these guys.

My setup works very well. And I have faith in this idea for people or manufacturers to develop. It definitely has a corner sharpness advantage over a dome at more open apertures. But once you get to f/13 or more closed down - I think it performs very similarly to a dome. I was always slightly frustrated that I could not get my 16-35mm @ 16mm to perform as well as the 20mm did - it would go blurrier towards the corners.

I haven’t adapted the Corrector to my Mirrorless camera (yet). This is partly because I use the Nikonos 15mm (a 20mm equivalent) with my Sony - which kind of does the same job (and is more travel friendly). And this is partly because I don’t have many Sony wide angles of my own to test - and don’t want to spend money buying lenses that I am not sure will work. Added to this, I would never shoot rectilinear as my main wide angle underwater - I just find the look of the images too low impact for my taste. I much prefer barrel distortion (fisheye distortion) compared to rectilinear for underwater shooting - so would always choose a WACP or WWL over a 16-35mm or similar for shots in this FoV range. Which means spending money on this solution is hard to justify.

Edited November 26, 2025Nov 26 by Alex_Mustard

I found a couple more links while searching the web:

https://g6yb.com/g3ynh/photography/articles/wconv_intro.html

Here is the important text:

"Rebikoff-Ivanoff corrector, in its basic form, consists of a plano-concave front element with a magnifying element behind.  It eliminates the optical distortion caused by a flat air-water boundary. The lens elements can be mounted in their own underwater housing, allowing the rear surface to be placed close to the flat port of an underwater camera housing.  If the intervening water layer is thin, the external lens corrects for the distortion caused by the port."

Interesting is that it can be used as a wet lens. How similar is this to existing wet lenses?

Another is this:

https://www.seafriends.org.nz/phgraph/film.htm

Here is the important text:

"Rebikoff-Ivanoff correction lens
Demitri Rebikoff was one of the pioneers in underwater photographic equipment in the era 1940-1980. He designed an underwater correction lens that is also a wide angle converter, based on an inverted telescope. Because it does not change the camera's focus, it is said to be a-focal. As shown in the diagram, this correction lens consists of a negative lens as port and a flat positive lens placed 30mm further towards the camera. The lens can be put together from the parts supplied by a technician for eye glasses. 
It has a number of attractive advantages, not the least that it can be used both above and under water. It is also used as a 'wet-mate' underwater attachment. The Rebikoff 'port' is often used for underwater television cameras, but it is disappointing for still cameras, and cannot match the sharpness of the Nikonos lenses."

Cutting and pasting brought in the figure.

Note the change in order of the names for both sources. Was this arbitrary? Nikonos lenses are better???!!!!!!!

10 hours ago, Tom Kline said:

"Rebikoff-Ivanoff corrector, in its basic form, consists of a plano-concave front element with a magnifying element behind.  It eliminates the optical distortion caused by a flat air-water boundary.

The Zeiss one is definitely more complicated. The front (main) part is not simply plano-concave. But it two elements sandwiched together, with the outer element being slightly convex. Also the internal lens is not a simple positive lens - but matched to the outer lens. Worried about loosing this lens, we measured its strength and made a simple replacement matched to the same strength, which didn't work anywhere near as well (showing there is something more in the design).

I know that I shared a lot of stuff about it on Wetpixel at the time. That Tom also contributed to. Search Ivanoff on Wetpixel forums - e.g.

https://wetpixel.com/forums/index.php?/topic/54681-full-frame-slr-wide-angle-corrector-port-tests/&tab=comments#comment-356001

Edited November 27, 2025Nov 27 by Alex_Mustard

On 11/25/2025 at 10:49 AM, Davide DB said:

The result is a rectilinear image, right?

Yes, very rectilinear Davide. My optical glas may be a slight variant, though.

As @Tom Kline asked for more historical quotations, I have found the following interesting recent writing from 2023, confirming the two-step process this optical system has gone through and what Alexandre Ivanoff's later role played in the 2-step invention. It's in fact the complex chromatic aberration correction lens element, that @Alex_Mustard had get measured and failed to reproduce with normal diopters. Have a read below...

source: Photonics Focus Magazine: Article on Page 14 by By William G. Schulz

But Rebikoff didn’t stop there. Studies of the eyes of fishes had revealed that any satisfactory photography underwater would be impossible through a flat glass or plastic porthole. The plane diopter effect makes the porthole the equivalent of a 3.4 diopter magnifier lens.

“Introduced into the optical path, [the lens] not only increases the focal length of the camera lens by 34 percent, restricting the field of vision by 34 percent in angle and about half in area, but also reintroduces all the optical aberrations, such as chromatism, sphericity, astigmatism, etc., that were so painstakingly removed from the expensive modern camera lenses,” Rebikoff wrote.

With Alexandre Ivanoff of the Paris Museum of Natural History, he then invented the renown Ivanoff-Rebikoff lens. “It is a reverse Galileo Telescope computed out of two new types of optical glass to correct fully all aberrations along with the focal length increase for the first time. It has proven since to be the ultimate improvement in underwater optics, applicable to all cameras, all optical

instruments, and the human eye.”

17 minutes ago, Adventurer said:

Yes, very rectilinear Davide. My optical glas may be a slight variant, though.

being completely different from the Zeiss design of Alex, could you share some photos taken with this lens?

On 7/8/2025 at 3:49 PM, Adventurer said:

Mine was not made by the famous Carl Zeiss, though. I think it was designed by fathom optics in the USA around the year 2000 for video shooters.

Is it this one?

Fathom Imaging

Corrector Optics - Fathom Imaging

CORRECTOR OPTICS Field curvature generated by a concentric dome port can be eliminated by inserting a precision lens assembly, “Corrector Group”, near the dome port concave surface.  The “Corrector Gr

Their patent:

https://fathomimaging.com/wp-content/uploads/2020/10/Concentric_Dome_Port_Correctors.pdf

On 11/27/2025 at 7:52 AM, Tom Kline said:

The Rebikoff 'port' is often used for underwater television cameras, but it is disappointing for still cameras, and cannot match the sharpness of the Nikonos lenses."

Cutting and pasting brought in the figure.

Note the change in order of the names for both sources. Was this arbitrary? Nikonos lenses are better???!!!!!!!

I suspect there are many versions of this lens floating around and design capability for optics has expanded quite significantly since these were originally developed. The statement above quite likely refers to what was available in the 1960s. By the 1970s the possibility of computer aided lens design appeared and was likely used with the Carl Zeiss lens Alex has and likely they were able to improve it significantly with additional elements or other changes like newly available optical glasses. So the newer Inanoff-Rebihoff correctors are likely to better optivally than the simpler ones designed in the 1960s.

Happy Thanksgiving!

Thank you Alex. Not surprised that Zeiss may have made some improvements, but a doublet (2 elements glued together) for the port would also need to consider pressure resistance. How would hydrostatic pressure affect the glass at the contact surface between the elements? Lens element separation is bad enough in air (have seen Z optics with this problem - both camera and microscope).

Thank you Adventurer. The 2003 article is interesting but may be misleading. It would be good to know how the author obtained the quoted material. It seems unlikely that it is from his memory if from 1968!! Rebikoff may have worked with JYC but it is Edgerton that JYC called Papa Flash. JYC is known to have had custom built underwater housings for his motion picture work. If Rebikoff worked with Ivanoff to invent the I-K lens per this article why is Rebikoff not in listed in the patent (other names (Grand and Cuvier) are)?

Rebikoff may have outlived Ivanoff so had more of a chance to blow his horn (as well as being the book author). Also note the differences in the figure captions I previously posted. System Ivanoff in 1955 then called Rebikoff correction lenses in 1965! For the same items. R does show the smaller lens (actually two of them) on his stereocam. R may have built the cam but I more likely (his company or his associates) the lenses that are part of the housing.

Thank you Davide. The Fathom unit seems to work more like the recent Sea&Sea correction lens as it is designed to work with a dome port but with 3 lenses elements so may be even more expensive. The S&S lens is aspherical and maybe it is doing the same job as 3 that are spherical.

Thank you Chris. These lens were first developed by 1955 as that is the date of the earlier book and there are more examples in it. The patent was submitted in 1951 (in France apparently), received by USPO in 1952. Suggests a bit earlier than the 1960s.

4 hours ago, Tom Kline said:

Not surprised that Zeiss may have made some improvements, but a doublet (2 elements glued together) for the port would also need to consider pressure resistance. How would hydrostatic pressure affect the glass at the contact surface between the elements? Lens element separation is bad enough in air (have seen Z optics with this problem - both camera and microscope).

Thank you Chris. These lens were first developed by 1955 as that is the date of the earlier book and there are more examples in it. The patent was submitted in 1951 (in France apparently), received by USPO in 1952. Suggests a bit earlier than the 1960s.

Thanks Tom, the point I'm trying to make is the earlier lenses, be they from the 50's or 60's are likely not as good as the Carl Zeiss version which it seems was designed in the 1970s when computer aided design and new optical glasses were appearing. This would possibly explain the remark the Inavnoff-Rebikoff correctors were not as good as the Nikonos lenses in the books.

Regarding doublet lenses perhaps yes if they are cemented doublets - they could have been air spaced doublets perhaps? Air spaced doublets provide an extra degree of freedom in the design due to the air space. If the front element were strong enough to resist flexing due to static pressure, as long as the join was inside the housing it would work as well as any cemented doublet I think? I understand cemented doublets become problematic in larger sizes and they were used as the polish and coatings required on the cemented surfaces were not as demanding as the cement filled defects and also avoided reflection from the two cemented surfaces.

12 hours ago, Tom Kline said:

If Rebikoff worked with Ivanoff to invent the I-K lens per this article why is Rebikoff not in listed in the patent (other names (Grand and Cuvier) are) ?

Good point, the patent was granted January 10th 1956 without mentioning the name Rebikoff.

The reasons for that are highly speculative.

However the Rebikoff / Cherney book you brought up called it "System Ivanoff" in 1955 according to you @Tom Kline as a trusted source. With that book being out prior to the patent and my other research that Rebikoff's Poodle ROV (dated approx. 1953–1954) had such or similar optical system mounted in front is an interesting circumstantial evidence of something I am not sure how to interpret.

Rebikov and Cherney would have clearly exposed the US Patent US2730014A by Ivanoff et. al. to a prior art risk.

This is a serious issue preventing any patent from being granted or after it has been granted preventing the owner from successfully enforcing or licensing it. This is also called risk of invalidating / novelty-destroying prior art or „risk of anticipation/obviousness in view of the prior art" -> meaning you cannot patent what's already out in the public domain. A book mentioning or prototype displayed on a trade show prior to filing is a common mistake by inventors for this. A comparable rule existed in the United States both in the 1960s (under the Patent Act of 1952, §§ 102/103) and already since the earliest patent statutes in the 18th and 19th centuries.

As the patent also says "Filed Feb. 19, 1952" your book copy needs to be inspected more closely for the exact publication date and edition index. I would be interesting to learn if this book was actually the first edition or earlier publications are flying around. It might also be a potential reason why the image caption was renamed from Ivanoff to Rebikoff in a later edition. We do not know though, if this was done by Cherny, Rebikoff himself or some clerk at the publishing company.

12 hours ago, Tom Kline said:

Rebikoff may have outlived Ivanoff so had more of a chance to blow his horn (as well as being the book author).

Seems not like that, ..

contrary to what you wrote: Alexandre Ivanoff (1917–2003) outlived Dimitri Rebikoff (1921–1997).

There are some Patents by Demitri Rebikoff online, his last filing looks like Oct. 31, 1990 for an optical diving mask restoring peripheral vision, citing the Ivanoff patent from 1956.

22 hours ago, Davide DB said:

Their patent:

https://fathomimaging.com/wp-content/uploads/2020/10/Concentric_Dome_Port_Correctors.pdf

[ . . . ]

Is it this one?

No. Cannot be, as that patent is too recent for having been applied to my lens.
As I initially wrote my Ivanoff-Rebikoff broadcast camera corrector front port is from "around the year 2000".

I actually did not realise that it is an underwater corrector port for a long time, as IR corrector ports look very similar to obscure flat ports from the outside. You have to inspect them more thoroughly or "weight-lift" them to get the idea that they might be something different.

Edited November 28, 2025Nov 28 by Adventurer

Another data point: I have the book titled Free Diving by Rebikoff translated by Mervin Savill. Published in London 1955, first published in 1952 in French as Exploration Sous-Marine

Ch. VII (the last one) is titled Underwater Photography and Filming. He writes a lot about his underwater flash units but not a peep about corrective optics

Interesting that Ivanoff lived so long but what did he do from the 1960s onward? Searching his name I came up with a living artist.

Another data point; See: https://www.spiedigitallibrary.org/conference-proceedings-of-spie/9192/91920P/Afocal-viewport-optics-for-underwater-imaging/10.1117/12.2061445.short

Read the abstract!!! He calls them "the Ivanoff corrector lens"

Lens is a bit vague since it can be one piece of glass or a whole unit like a camera lens, but for lack of a better English word lens has to be used (Abstracts often have a word limit (based on a lot of experience)). This is from 2014 so relatively recent.

At Chris: the Nikonos opinion is from a current web page so would seem to be not too out of date but maybe limted to the experience of the author(s).

I remember when the blue housings were released! It was during the 2 years my family lived in the US (Germany before and Japan after) when I bought the Hasselblad issue (house magazine) on it at a local camera store. This was between Sept 1970 and August 1972. So it is about 2 decades post Ivanoff earliest dates from the patent.

BTW the first Hasselblad to use the 38mm lens was called the Supreme Wide Angle or SWA. The SLR was the 1000F. I have seen a SWA in person - it had a more primitive shutter. From the early 1950s. The SWC, the later camera, has to be used in the blue housing that takes the corrector lens. SWC/M and newer, no, because the tripod mounting shoe was moved to allow fitting of Polaroid backs.

Edited November 29, 2025Nov 29 by Tom Kline

somehow I screwed up and the text goes beyond the page!

28 minutes ago, Tom Kline said:

somehow I screwed up and the text goes beyond the page!

Fixed it - I copied and pasted the text, copy using ctrl-C then pasted using Ctrl-Shift-V. Did you paste the text in from somewhere? If so try pasting with ctrl-shift-V.

I wrote it live so to speak but I did have to scroll up and down quite a bit to see the prev mssgs

super keyboard challenged