My first underwater test of the Sigma 15mm Fisheye behind the Zen 4″ Fisheye Dome Port on the Nikon D3s in a Subal ND3

Finally after successfully cutting off an amount of the shade on my brand new 15mm Sigma Fisheye lens I have managed to get it behind the Zen 4″/100mm fisheye mini dome port and get it in the water. The reason why I wanted to do this was so that I could take CFWA (Close Focus Wide Angle Photography) on a full frame underwater camera system. The Zen 4″ is an awesome piece of gear and although it does come with a hefty price tag, the workmanship and quality makes it worth every single dollar – I bought mine from Backscatter.

Keeping it simple – to achieve CFWA you need to find a nice fisheye lens that allows you to focus very close to your subject. Unlike larger dome port, the distance from the front of the lens to your subject is a lot shorter when using the Zen 4″ mini dome port, therefore allowing you to focus closer in on those small subjects which can allow you to achieve a pleasing photograph. Up until now, the most common lens that works perfectly with the Zen 4″, is either the Tokina 10-17mm or the Nikkor 10.5mm. With both of these lens not being suitable for a full frame camera, the Sigma 15mm fisheye with its very close focusing abilities, seemed the obvious choice. Sadly out of the box, the metal shade to this lens hits the inside of the port preventing you from fixing it to the camera housing. With this in mind, there are not many people out there willing to risk buying and chopping up a new lens to just see if it works behind the Zen mini dome and so I have found information about this set up very limiting.

Having a full frame Nikon D3s, I really wanted to give it a try as I believe the results will be great from this camera and so I took the risk of cutting down a brand new Sigma lens and buying the Zen 4″/100mm Fisheye Mini Dome. The following is the first of three tests to see if Sigma full frame 15mm Fisheye lens works behind the Zen 4″ dome port on the Subal ND3 with the Nikon D3s. The goal of this first pool test was just to see if the lens focused properly and just how sharp my initial test shots could be. I am quite pleased with these initial results although the next test will more focus on corner and subject sharpness from f2.5 through to f22.

The following photographs have not been sharpened – click to enlarge.

Shaving the Sigma 15mm Fisheye down for the Zen 4″/100mm Fisheye Mini Dome Port


So with the new Zen 4″/100mm fisheye mini dome port on my desk all the way from Backscatter, its time to get shaving. Shaving what? – well to get the Sigma 15mm full frame fisheye lens behind the Zen 4″/100mm Fisheye Mini Dome Port I first have to cut off an amount of the shade off the lens. Obviously taking a saw and cutting up a brand new $600 lens needs a little research first and after finding a lot of web sites with some even offering to do it for you, I believe I have picked the best bits of advice and come up with the following.

Tools for the job:

  • Not one site suggested using a Dremel Multi-tool and so I used one – why? because i’m not patient enough to use a handsaw, the handsaw blade had to be a special type (straight teeth or something), it would take up to 30 minutes to cut off just one shade and the finish can be a bit untidy. Instead I opted for a steel cutting disc attachment and a steel sanding attachment for the final finish.
  • Of course a dremel can be a little untidy if you go mad or it gets out of control so the next thing I needed to have was a perfect guide – a large Jubilee Clip
  • A Pencil to mark where I needed to cut.
  • An Air Blower – I used a hand blower so I could remove the fine metal shavings that got everywhere while I was cutting.
  • Something to Protect the Lens while cutting. This had to be something rigid/sturdy and that fitted perfectly inside the shade. I chose a Sea & Sea YS250 PRO strobe cap – I had one damaged that was hanging around. What better use for something that was responsible for the flooding of one of my strobes.
  • Black paint.


My secret to success during this whole procedure was taking my time. The Dremel is a great tool for the job but its easy to put it on full power and go crazy!
Because the shade to the Sigma is made of metal I needed the right cutter – I found this to be perfect.
Preparing the lens was very easy. First I established just how much I had to shave off and once calculated, marked with a pencil. The next stage was to carefully fix the jubilee clip which was to act as a perfect guide for the Dremel cutter. I made sure that the screwing section was away from the area that I would be cutting. The next thing I had to find was something that would protect the lens from the tiny fragments during the cutting process and just in case I slipped with the Dremel. Amazingly an old strobe cap fitted perfectly behind the shade. The next stage was to go to a well lit area away from camera housings etc. and start cutting.
The whole cutting process was so easy. I put the Dremel on a nice speed and let the tool do the work, keeping it flush up against the jubilee clip. I was very much aware that at certain points while cutting through the shade I was also cutting through the plastic cap. However, with the cap having a thickness of about 3mm, this did not matter. Once both shades were cut off I then used the blower to remove as much of the metal shavings as possible. Eventually once satisfied that it was pretty much clear of filings I removed the old strobe cap/lens protector from the lens and again blew the remaining filings away (at no point did i use a cloth to polish the lens). I had perfectly shaved off an amount of the shade without trashing my brand new lens. The final stage was to very carefully sand down the cut surface which was quite sharp in places. I did this using the Dremel on a very slow setting.
Placing the lens onto the camera and into the housing I put a small amount of toothpaste on all four corners of the shade and slowly placed the Zen port into place making sure that I had cut off enough of the shade. The trick with the tooth paste was that I found it tricky judge whether I had shaved enough of the shade off. With fear of scratching the inside of the port, the tooth paste would act as an early warning just in case I had not. With the port securely fitted the next thing was to check if the shade touched the inside of the port during focusing. Again, its tricky to see so the tooth paste is a perfect guide.
The end result – with a nice perfect finish and a lick of paint, I have managed to get a full frame fisheye lens behind the Zen 4″/100mm Fisheye Mini Dome Port……..sorted! 😮