Acrylic vs Glass dome ports

We all like good lenses. The wise say that you should first invest in glass over a fancy and hi end camera body. We never have enough of them and there is always the will to buy another one.


Each focal length is a new perspective, a new possibility what means less boundaries to our creativity. Comfortable zoom lenses, high quality primes - all are there to project our idea to the camera sensor with possible best quality. But as the underwater photographers we know that there is something more in between of the lens and our subject. On the land we have air there, so we don’t have to care much, but when submerged into the underwater world we have to put one more thing in between - the lens port.

At the first glance it is just an extension of the housing, made to protect the camera from the water and pressure. But as we dive more into it we realize that in fact it’s another optical element on the way of the light. The correct or wrong lens port can completely change our experience with underwater photography and decide on our results.

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There are many details which we have to have in our minds. The Lens and the Lens Port has to work as a team and we can’t just pair them whatever we like. As the front element separates the water from the air it has to make it in the most correct way, so the field of view is not affected, no aberrations are added and project the image to the lens in such way, so it can focus properly.


Now we can see that it is quite important how and from what material the lens port is build. And talking about wide angle photography all becomes even more complicated as we really want to preserve that field of view. The water and the air bends the light in a different way and passing from one to another everything gets magnified more or less by 25%. Apart of that, the light splits like in a prism so chromatic aberrations are induced and our image suffers from less contrast and clarity.

The Dome Ports were invented to overcome that problems. Sphere surface magnifies the image by 0.7x and by bending the light in different way reduces the prism effect. Well designed dome port allows us to take advantage of wide angle lenses underwater. And as it was said before they can work together as a team for the best results. Choosing the port we have to pick between different sizes (from small 4” to huge 8” spheres), place the dome exactly in the field of view of the lens (that’s why there are different lengths of extension rings) and choose between the material is made out of: Acrylic or Optical Glass.


Let’s focus on the last part. What's the difference between those two?


Acrylic domes have whole lot of advantages. They are easier to manufacture, so the price is significantly lower than glass. They are lighter, not as easy to break and in case of scratch that can be polished even by ourselves at home.

All these together give us very nice product which serves well for the most of the users. During my whole career I was always using acrylic domes as it’s very affordable option providing good results in most of the situations. When I have switched to Sony and started to use SeaFrogs equipment I went directly for 8” dome which paired with ultra wide angle 14mm lens gave me good image quality underwater with fantastic possibility of split shots. Even if the size of the dome is very big it is lightweight enough to handle it easily.


But there are no roses without the thorns. So acrylic domes have their downsides.

First of all is the softness of the material. Even taking care very much about your equipment is impossible to avoid more end more of little scratches appearing on the surface of the dome. Even if they are very small and hard to see slowly they are decreasing the image quality, especially in high contrast situations. As I have said before there is way to fix it polishing your dome, but it’s not the most comfortable solution. Even basic cleaning is a bit complicated as its quite difficult to get the surface perfectly clean, and we have to be very careful using cleaning products as they can react with the plastic.

Apart of scratches acrylic in general isn’t as good optically as the proper glass is. So there are more artefacts visible if you know where to look for them. Like purple fringes around high contrast edges or lower sharpness at the corners with the lens wide open.

All this leads us to the situation that at the some point you may consider to upgrade your dome to the proper optical glass one. At higher price tag we get better image quality, more durability scratches (but hey its glass, so don’t hit it as it can break quite easily!), and if well paired with the lens it offers better quality on the edges. Glass gives also possibility of coating which helps to fight with the chromatic aberrations therefore provides better contrast and details. Since not so long there is 6” Optical Glass dome in SeaFrogs offer, so If we are looking for higher quality of our photos now we finally have this option.

During my recent trips to Maldives and Mexico I had opportunity to test that new dome and here are my thoughts.

As a person used to big 8” dome the 6” looks small and handy. It’s very nice to travel with but I was worried about corners quality (bigger ports usually gives better sharpness there) and possibility of my favorite “over and under” split shots. My idea was to use it mainly with Sony G Master 16-35mm f2,8 which is my new main lens, but wanted to test it as well with my all time favorite Samyang 14mm f2,8.

The very first thing I have noticed getting into the water that it doesn’t float that much and has less drag comparing to the 8” acrylic port. For a freediver photographer is a good thing as I can be more agile moving around.

But the most important: the image quality. Improvement is visible from the very first moment. No matter how much I took care about my previous dome I could never get it perfectly clean and clear, what could be easily seen on the photos. With time I kind of got used to that lower clarity and didn’t realized until now how clear the image can be. Especially the counter light shots witch very high contrast is where the new dome shines. Already in Maldives while doing photoshoots I could easily see that there is no halo around my subjects while having them lit by strong sunlight on a deep blue background. Same with sharks or stingrays.

After visiting few Cenotes in Mexico I could already tell that is where this dome really shows it’s strength. In such high contrast situations I had no problem shooting counter light maintaining fantastic clarity and the detail.

The dome with long extension tube pairs just right with the 16-35mm. The lens sits perfectly on the bottom of the port taking advantage of the whole sphere. It provides very nice sharpens on the corners. Wide open to f2.8 the image is a bit softer there, but its normal behavior and I can’t complain. The lens itself is extremely sharp, and optical glass of the new dome doesn’t reduce it. Shooting some portraits on 35mm was really hard to believe how many details there are on the photo.

2’ less of diameter and 2mm focal length made it more difficult for the split shots. With calm surface It was still possible to get decent shots, but with a bit more waves it is more problematic but still doable and I have few shots which I really like.

But talking about the split shots there is one very big advantage over the Acrylic dome - the water drops! The nightmare of “over and under” doesn’t apply to the glass! It’s way easier to get clean surface of the lens as the water doesn’t stick so easy to the surface of the glass as to acrylic one.

Underwater is not so easy to do side to side comparison, But here you can se the behavior of the domes in similar kind of shots where you can see the higher contrast of the glass dome. Pay attention especially to the areas around of high contrast objects.



It is something what I was really missing on my photos and it will become my main setup until the 8” glass dome is not going to show up.

As I really enjoy freediving in caves or shipwrecks, I was curious how smaller dome is going to perform with Samyang 14mm f2,8.

With the available short extension ring the lens doesn’t sit perfectly inside the dome, is approx. 1,5cm too close to the dome so we don’t take advantage of the whole sphere and it affects the image quality. Not only corners, but even the edges are more blurry than I would accept. Placing main subjects close to the center helps, but it’s limiting the framing possibilities. Probably if Seafrogs comes out with a bit longer extension ring the situation would improve. So far I can say that its ok to use, but the quality is far from top.


After over 2 months already the glass port is an essential part of my underwater setup. I don’t miss the 8” acrylic dome at all and definitely I can tell that it gave a step forward in the quality of my work. Therefore I highly recommend it.

Article and photos by: Wojciech Dopierala

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