Isaac Szabo

Interesting comparison. Nice work. One thing to note is that it appears that the APS-C crop mode was turned on for the Canon 60mm shot (I think the default setting is for it to turn on automatically when you mount an APS-C lens). Both the Canon 60mm and Sony 50mm are 1:1 macros and will have the same magnification at minimum focus distance.

Yeah, I'm not sure there's a way to ensure a good fit on the first try without me putting in more work than I have time for right now. But with your local printer it might be a good idea to try for a fit that's 0.1-0.2mm looser than you want to try to account for the slight bulge from my waterproof settings.

You're right that sub-millimeter tolerances are not guaranteed to be maintained across different printers, materials, and settings. As an example, I was recently testing the accuracy of my two printers using a 100mm diameter test print. My main printer had a maximum error of 0.22mm, which I decreased to 0.09mm after some adjustments. However, my newer printer (different brand, different slicer) had a maximum error of 0.51mm, which was larger than I expected. I'll also note that one of the aspects of my waterproof print settings is around 20% overextrusion, which leads to slightly swollen dimensions compared to normal settings.

This is why I don't use neoprene covers. Of course, whatever cover/cap you use, it is important to dry off the glass before the water has a chance to evaporate.

I too feel that the other RS lenses aren't particularly interesting, and I think the 20-35mm would be more complicated to rehouse in a donor lens due to the zoom. I do have interest in trying to convert the Sea&Sea 12mm and the Nikonos 15mm when I have some free time.

Unfortunately there's not. Perhaps I could try converting a Canon donor lens at some point in the future. But it's a significant undertaking, and I don't anticipate having the time in the foreseeable future.

Thanks for testing that, @MarkRD! Hopefully I'll be able to offer an N120 port within a month or two.

Following up on this, I tested the 13mm inner lens behind a 9" dome port and wasn't impressed. I suppose the images could be usable in a pinch, but sharpness wasn't as good as a regular fisheye behind the same dome.

Really interesting info, @MarkRD. Thanks for sharing. I had assumed the Monster screw drive adapter was working reasonably well on Sony cameras since Seacam was advertising it, but your experience makes me wonder. It's too bad that stacking the adapters didn't work for the Nikon Z camera. I'll try to figure out away to test my Sony converted 13mm with a Nikon Z adapter in the near future.

Yes, the parts are waterproof on their own. If you were to use normal print settings the parts wouldn't be waterproof, and you would have to do something like cover them in epoxy to make them waterproof. I used to smooth out the o-ring surfaces with epoxy or by turning them on a lathe, but then I discovered that it wasn't necessary.

I'm not sure I'm completely following you here, but no I haven't noticed that any extra care is needed. The ridges from 0.10mm layers are not very significant.

Yes, there are many variables at play including material type, printer model, nozzle size, and many different print settings. One important aspect of 3D printed o-ring groove walls is a small layer height. I use 0.10mm. Obviously, the walls won't be completely smooth due to the tiny ridges of the layers, but the compressed o-ring will span enough layers to make it watertight. For example, a compressed o-ring with a 1.5mm flat surface will span 15 layers. Using large/soft o-rings helps with this.

My 13mm port has 6mm thick walls. I had planned to pressure test different wall thicknesses to failure and plot the results so I could have actual data on how thick the walls needed to be, but even the thinnest port I tried survived the max pressure of the chamber. So I didn't have a meaningful reason for going with 6mm other than that it seemed like it was much more than adequate. I recently got a stronger pressure chamber and tested the port down to 145psi/100m/330ft with no issues. I use PETG. I've tried a number of other materials (including some more expensive/exotic), but PETG has a number of advantages over the others I tried including good print quality, water resistance, layer adhesion, toughness, price, etc. I'm very busy at the moment fulfilling 13mm conversion orders, but I might be willing to print your design for you if you want since it might be difficult to find someone else who has the waterproof settings dialed in.

Standing on an aluminum can is not similar to a pressure differential. Instead you can put your mouth over the opening of an empty can and suck the air out. The can walls will collapse with little effort. Those are issues when trying to dial in the ideal print settings, but you only have to go through that process once. After you've figured them out you can apply them to all future projects. Of course those are viable options too. They're just more expensive/difficult. I'm guessing you might be able to buy a 3D printer for the cost of having a port machined (unless you can do the machining yourself).

I use 3D printed ports and have done some pressure testing. At one point I was trying to get one to fail so I could better understand their limits, so I made one with intentionally thin walls of only 2.5mm (I normally use more like 5-6mm). Surprisingly, it withstood the limit of my pressure chamber which equated to 225ft/69m. So 3D printed ports/extensions can certainly be a viable option. However, FDM 3D prints are not watertight using standard printing settings, and figuring out the right settings can be difficult. There are other challenges too including lots of CAD work, dimensional tolerances, and as you mention the horizontal overhangs. It can all be figured out, but it will probably require quite a bit of work/experience before one gets really good results.

For what it's worth, Alex's link/website seems to be working properly for me. I'm skeptical of the virus claim.

Unfortunately, I wouldn't expect that to work well. If you try shooting the inner lens topside, you will see that the image quality is good in the center but degrades towards the edges. I think the inner lens needs the 13mm front element and to be underwater in order for the edges to sharpen up. That said, I haven't tried it underwater with a regular dome, so it might be worth trying just in case. I'll also note that you can shoot splits with the 13mm in calm water, though obviously a large dome is better for that.

After thinking about this more, I don't expect the 16mm to work well as a substitute for the inner lens. The inner lens, when modified so it can focus on land, has poor edge sharpness. This tells me it too was likely specially designed for underwater, not just the front element. I'll still try it out though, just in case.

I have read somewhere that the 13mm optical design was based on the 16mm, and yes, the diagrams do look very similar. I have my doubts that they are the same excepting the front element, but perhaps I should purchase and disassemble a 16mm and try to find out. Edit: I went ahead an ordered a 16mm. Even if the optics don't turn out to be identical to the 13mm, they might be similar enough to work well behind the 13mm front element. And if that's the case, perhaps Andrej can still supply the front element, providing an alternate pathway for people to acquire this lens.

The low cost of the 50mm certainly played a role in me choosing it. The conversion would be less viable if an expensive lens had to be sacrificed.

I can do my conversion with just the individual glass elements. It is Andrej Belic of NJU System who has had replacement front elements made. The first 13mm I bought to experiment on had a scratched front element. Several years ago I contacted Andrej about the cost of sending me a replacement and was quoted 1000 € plus shipping. I wouldn't necessarily say it was serendipitous that the 13mm elements fit inside the Sony 50mm. I put a lot of thought/research into which donor lens to use, comparing optical and mechanical designs, etc. I selected the 50mm because I determined that it was the best candidate.

I believe a little over 2000 were produced, though that was 30 years ago, so who knows how many are still around. All I really need for my conversion is the glass itself, and since the optical formula is known, I do wonder about the possibility of having an optics company reproduce the elements. I just worry the cost might be too high, but I don't know for sure.

The $3K one has been lowered to $2.7K, but that's still high in my opinion. Currently it seems like most of the ones available at reasonable prices were bought up over the last couple months and now there's a shortage. Hopefully more show up on the market before too long and the prices don't get outrageous.

The FCP looks like a great option for those wanting the added versatility of a zoom and circular fisheye. But yes the 13mm offers advantages in image quality, size/weight, and price. A few measurements of my 13mm port (including hood): Diameter: 108.6mm/4.28in Length: 108.3mm/4.26in Weight: 519g/18.3oz Note that the weight might be slightly different since I weighed a prototype and the final version has a few minor changes.

@Barmaglot That's basically correct. Though I will note that $3500 USD has been on the high end so far. Obviously, it all depends on how much one spends on the 13mm. Several people have recently been able to purchase them for between $1500-1800, and the one I'm currently starting work on was somehow snagged for $1200. That said, I'm sure if demand increases your figure will soon be more typical.