Hi all

I see that Seacam has just launched tonight a new type of water contact optic seems it is designed to work with rectilinear lenses (16-35 range) and designed to give the same performance as in air. It uses an Ivanoff-Rebikoff lens system Called the Optical Precision Port it uses what looks like a relatively small flat port and a correction lens that is screwed in the front filter threads. Seems like it is very compact and travel friendly, though perhaps not particularly wallet friendly. Here is a link to their website, scroll down and click on the link "12 month practical test for some more details on the optics." A friend of mine Don Silcock did the field testing.

https://www.seacam.com/de/optical-precision-port/

Believe Zeiss many years ago developed something similar for the UW hassleblad system.

Since I will be attending the DEMA Show in Orlando Florida this week I will be sure to swing by the Seacam booth to have a look (provided they bring one) at this new lens to see what it is all about.

Looks like a very clever design: https://www.seacam.com/en/optical-precision-port/#6910ccd3bd523-4

It is modular making transport a bit easier. Part of it is a dedicated large diameter (providing buoyancy) port extension. Seacam could build alternates to accommodate other lenses. Ask them about this at DEMA.

On 11/7/2025 at 3:31 AM, Chris Ross said:

SNIP

Believe Zeiss many years ago developed something similar for the UW hassleblad system.

Correct! Alex Mustard has this and wrote about it some years ago after having it modified for his Subal housings. It was originally designed for the Superwide camera that had a fixed 38mm lens for the 6x6cm format so had a 90° angle of view. A bit narrower than what Seacam has come up with. As well the internal lens was for the Hasselblad series 63 filter size (same as series VIII, threading on internal lens same as filter retaining ring), quite a bit smaller than the corresponding part for the OPP.

What an irony 🫢🤣 I am diving my Ivanoff Optic now for 6 month at a fraction of the costs and with more corner sharpness I observe in the sample images on the Seacam page and in the teaser. But I am sure Seacam users will buy this anyway.

Glad to see some general progress and competition in the underwater optics field again.

I'm happy to see some innovation from Seacam here. Although I'm not sure it's for me - I've been happy with the 16-35 PZ and compact port, and corner sharpness hasn't been an major issue except at CFWA.

Couple of things I'm curious about:

1. Is the field of view of the lenses the same as on land?

2. Which of the major lenses are compatible? Can we use say a 24-105?

3. What's the weight - they say "similar to the superdome" which is 2950g. The compact port is 1850g.

4. What are the dimensions, weight, prices, diameters of the optical correction lenses? The one shown at the page is 77mm, but Sony's 16-35 are either 82mm (GM/GMII) or 72mm (PZ/Vario-Tessar). Canon is 82 or 77 and Nikon 77mm. I'm sure they've thought about this.

Doesn't sound travel friendly if those weights are correct...

Seacam did a live post on Instagram where some of these details are revealed (can still be watched). Weight is 2.9 kg but is compact if one dismantles it. Stuff can go inside the empty port extension. The two optical parts are flat so a bit like oversized hockey pucks - the larger one, the front port is about 18cm in diameter but only 4 cm thick without the shade, 6cm with. Thus far only lenses with a 77mm filter size but I would not be surprised if an 82mm version might be on the horizon. The Nikon 16-35 is fairly long so a shorter, squatter port extension might be in the future for other lenses. Hence my question above.

PS. I suspect mainly lenses that keep a fixed length will have to be used.

PPS. 5000 Euros plus taxes, shipping etc.

11 hours ago, Adventurer said:

What an irony 🫢🤣 I am diving my Ivanoff Optic now for 6 month at a fraction of the costs and with more corner sharpness I observe in the sample images on the Seacam page and in the teaser. But I am sure Seacam users will buy this anyway.

Glad to see some general progress and competition in the underwater optics field again.

Pleeeeaaase show the Ivanoff-solution?

36 minutes ago, fruehaufsteher2 said:

Pleeeeaaase show the Ivanoff-solution?

I did quite a while ago in this forum.

It is very funny how similar it looks to the new Seacam solution. However it‘s noteworthy that I can use mine without a 2nd component on the lens:

Thread name:

Ivanoff Style underwater corrector port on a Canon Marelux MX-R6II

Edited November 10Nov 10 by Adventurer

Found!

Thanks a lot

Thanks for posting the link to the previous thread which I had missed. I looked up the references in that thread. Note that the description in the Ivanoff patent indicates two lenses named 1 and 1'. Shown as well in the figures (but a and b in Fig 5). If your Ivanoff port does not contain both of these lenses it is incomplete. Lens 1 (or a) is the replacement for a dome port but only curved on the inner surface, the front surface being flat. To accommodate the curvature the front port is thick at the edge is hence a negative lens. The correction lens (1' or b) is a negative lens, thicker in the middle.

Edited Tuesday at 10:11 PM5 days by Tom Kline

13 minutes ago, Tom Kline said:

If your Ivanoff port does not contain both of these lenses it is incomplete.

Nope. It‘s complete as it is and delivering dent sharp underwater images. All required optical elements are included in the main module. There is Ivanoff style and Ivanoff Rebikov designs, plus multiple variations derived from this principle.

Very interesting clip. But at approx 4.40 he says 'we increase the depth of field enormously'... 'so you can focus on the glass'.

I would love to see some hard data on this DoF increase.

4 hours ago, dentrock said:

Very interesting clip. But at approx 4.40 he says 'we increase the depth of field enormously'... 'so you can focus on the glass'.

I would love to see some hard data on this DoF increase.

I concur with your skepticism! In my experience focus is critical even with fisheye lenses which have a lot of DOF - (focusing evident because of focus breathing which is visible when changing pix quickly such as in the Lightroom "film strip"). Also interesting is that the port can do 120°!! This means that a 14mm should be possible. Main requirements seem to be the need for a front filter thread (so my old Nikon 14/2.8 lens is out) and a non-extending lens for either focus or zoom. He also answered my initial question which was related to the obvious modularity of the port.

Edited 18 hours ago18 hr by Tom Kline

I am excited to see Seacam exploring this idea. And keen to see more sample images - as the one test shot on their website looks both distorted and with very poor corner performance. Which I find somewhat surprising as I found this technology gave good optical performance (up to a 20mm wide angle on full frame).

I shot with an Ivanoff style port for several years, and was very happy with its performance, but have not bothered adapting it to my current housing yet - and have been using the smaller Nikonos 15mm to fill this niche instead. Here it is on my Nikon D5 in 2015.

I used the optic quite a lot for a couple of years and took many well known images with it.

Such as this photo from the Wildlife Photographer of the Year:

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 the

And also this photo, which will be seen widely in the coming months as it is the main promotional image for the forthcoming BBC Blue Planet 3 series:

Could you be a part of Blue Planet III | BBC Earth

We are currently on the lookout for captivating and unusual animal behaviours from the marine world, and would love your help. Some memorable BBC nature sequences began as observations by wildlife ent

As well as others.

Rebikoff was the one to claim extreme depth of field for this lens (see figure 6.13 in Mertens 1969) but I never felt this was especially evident in my pictures. This is shot with the port - and shows minimal depth of field can be achieved:

https://www.amustard.com/library/fifteen/CAY15_am-101945.jpg

For me the downside of the system is that the look was too rectilinear! Topside photographers always think that fisheye distortion is something that we'd want to avoid underwater - but actually it is the barrel distortion of fisheye lenses than makes many underwater wide angle pictures immersive. Non-fisheye wide angle images often feel stand-off-ish. So carrying the weight of this port around for the few wide angle shots I don't want to have a fisheye look, is the main reason I'm not currently using mine.

But overall I am excited to see this option being explored and developed. If it works it would be easy to adapt to any housing. I look forward to some sample images that show decent corner performance on 16mm wide angle lenses. Mine gave exceptional image quality with my 20mm lens - but the corner performance was not great when I used my 16-35mm with it.

Edited 17 hours ago17 hr by Alex_Mustard

Thanks for the pointer Alex, I had to look it up!!!

On the page above Fig 6.13 is point #4 (a list of the correction port properties):

"4. The depth of field is increased about a factor of 2 over a plane port with the same camera lens and aperture."

This sounds to me more a benefit of the de-magnification effect (1.33x eliminated) compared to a plane port. Mertens has a long discussion on depth of field and gets into loss of aperture due a plane port, compensating by changing distance, etc. There is also Fig. 6.17 that would be much better in color as there are 8 lines if I counted correctly. It would have been more interesting if Mertens had compared to a dome port as well.

Based on the caption in Fig. 6.14 the examples of I-R port in the book (Fig. 6.13 same swimming pool) were shot with a 21mm Super-Angulon lens (made by Schneider for E. Leitz), f/4 and f/3.4 max aperture versions made by then; as well as M (Leica Rangefinder camera) and mirror lock-up versions (for the Leicaflex as the Leica SLRs were named back then)). These lenses are of the non-retrofocus type not too dissimilar to the 38mm lens your port was designed for.

1 hour ago, Tom Kline said:

This sounds to me more a benefit of the de-magnification effect (1.33x eliminated) compared to a plane port. Mertens has a long discussion on depth of field and gets into loss of aperture due a plane port, compensating by changing distance, etc. There is also Fig. 6.17 that would be much better in color as there are 8 lines if I counted correctly. It would have been more interesting if Mertens had compared to a dome port as well.

I'd agree with that from practical experience. That this is relative to flat port, not a dome port, which of course, is what we’d be using these wide angle lenses behind these days.

5 hours ago, Alex_Mustard said:

I am excited to see Seacam exploring this idea. And keen to see more sample images - as the one test shot on their website looks both distorted and with very poor corner performance. Which I find somewhat surprising as I found this technology gave good optical performance (up to a 20mm wide angle on full frame).

I totally agree to your impression and did not understand why Seacam picked this particular difficult focal length to run their tests and first Ivanoff-Element (the part that screws onto the lens).

It‘s worthwhile mentioning that a Rebikoff-Ivanoff optic will not be designed for zoom flexibility and you run into similar entrance pupil positioning issues as with wide angle zoom optics behind a dome port. The Ivanoff-Element is the part that will make your system afocal again and tries to get rid of chromatic abberations etc. The optical designers of the Ivanoff Element will have to make compromises in optimally correcting it for different zoom positions. When the lens is off these positions the underwater photographer will have to sacrifice IQ.

As with Domeports and Watercontact Optics finding the right „Symbiosis lens designs“ from the topside lense choice will keep playing the critical role.

5 hours ago, Alex_Mustard said:

I'd agree with that from practical experience. That this is relative to flat port, not a dome port, which of course, is what we’d be using these wide angle lenses behind these days.

I found a reference that states that a dome port gives increased depth of field in water compared to what you would get from the same lens in air. This is due to the object being compressed into a virtual image close to the dome. Whether the Ivanoff optics work from a virtual image I don't know, but I expect that it quite possibly could. They give an example of a 24mm lens at f8 imaging an object at 1m distance having 563mm DOF UW and 424mm in air. Here is the reference, scroll down to section 4.

https://pmc.ncbi.nlm.nih.gov/articles/PMC4732081/

Without doing a detailed analysis, it's basically guesswork as to what is going on as the Ivanoff optic is neither a dome or a flat port. A flat port is limited to a field of 96° by Snell's law, but a 16mm lens has a field of view of about 106°. Odd things can happen with some optics UW, the Nauticam FCP for example seems to suffer from reduced depth of field based upon posts from users when it was first introduced.

2 hours ago, Chris Ross said:

Ivanoff optic is neither a dome or a flat port.

Chris we have to stay sorted here, so everybody is on the same page and not mixing things up. There is no such thing as a sole Ivanoff optic working standalone and making your underwater image better. There is just Rebikoff-Ivanoff Optics, where the Ivanoff Element does Step two of the optical correction. Contrary to sole Ivanoff Optics, the Rebikoff corrector port can have a positive effect with increased IQ when used alone, simila but still different to a dome port. The Rebikoff corrector port will look very similar to a flat port when viewed from the outside, mounted on a housing. So for everybody going first time into this, there is:

• Flat Ports

• Domeports

• Rebikoff uw correction Ports

• Rebikoff-Ivanoff uw correction Ports

Edited 6 hours ago6 hr by Adventurer

2 hours ago, Chris Ross said:

Whether the Ivanoff optics work from a virtual image I don't know, but I expect that it quite possibly could.

Not an Ivanoff Optic but a Rebikoff Underwater correction port will also create a somewhat „virtual image“ similar to a dome. Contrary to dome port the corrective effect can already be seen in air, but the image is not improved in air.