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 8Jul 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 9Jul 9 by Adventurer
added link for direkt download PDF at amazonaws