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Domes are ideal for underwater and split-level (half over/under) photography, because they correct for aberrations that occur as light travels at different speeds above and below water. Outex ports, including domes, are made of optical glass.
These examples illustrate some common issues addressed in this entry. We get into additional detail below. Photo below using Outex Pro Kit + Dome 180mm
Outex Pro Kit flat vs. dome optical glass ports side by side comparison. Outex dome ports come pre-packaged in a neoprene protective case to help store and protect them.
As with most things in image-capture, there are a number of factors that influence the results, including the camera, lens, focal length, the settings used, lighting intensity & angle, composition, distances between the camera & subjects in the composed frame, as well as the clarity & opacity of the water.
There's no right or wrong when it comes to photography or cinematography. Only desired outcomes, and the creator's ability to execute/achieve that vision or objective. The Outex system is designed with that in mind. The system is modular, and allows you to use domes or flat ports interchangeably, depending on what you'd like to accomplish. You can learn about the benefits of the domes in other entries of our Questions/FAQ page. For example, here.
For additional information explore other entries on our website on this subject.
Flat lenses are comparitively inexpensive, smaller, and lighter than dome ports, and they work well underwater, just as they do above water. But they have physical limitations underwater, and those limitations are exacerbated when trying to capture split level (over/under) shots. Outex is one of the only manufacturers offering glass ports (not plastic or acrylic), which is optically superior in both conditions. Both flat and dome Outex lenses are made of American or European professional-grade glass. And as most of the Outex underwater photography system, our lenses, both flat and domes, are modular and compatible with all of the housings/covers, and accessories.
All of the Outex flat lenses screw onto your lens' filter thread (just like a UV filter or polarizer) and can work with any lens. But some lenses, such as unthreaded, fisheye, or hooded lenses do not accommodate a filter thread and often have curved lenses in the front. Those require one of the Outex dome ports. Both Outex domes work with any lens in the market, past, present, and future, because the domes are designed to be universal, and anchor to specific lenses thru adaptors or clamps.
Outex dome adaptors match the lens filter thread size, just like our flat ports would. We support all thread sizes.
Outex dome clamps anchor to the lens thru an adjustable clamp, and connect to the dome to optimize optical properties based on placement, as well as maximize stability as an additional anchoring point within the housing/cover.
The two Domes use different adaptors and clamps engineered to optimize optics and usability of each. And both are available in Accessories as kits (bundles of products) as well as in Parts where you can purchase all of our products independently. You just use different adaptors or clamps over time as you needs evolve.
Using Dome 120mm vs. the Dome 180mm is not a definitive difference maker, just as using different lenses. As explained above, the larger dome increases the variety, frequency, and compatibility of your use with your camera, lens, and set of conditions. In other words, the larger dome make it easier to "get the shot" more often, regardless of what equipment you're using, and the conditions. The smaller, more travel friendly, more affordable dome can yield the same desired outcomes. But it may force you to work "harder at it" - meaning a "more controlled" set of variables like camera, lens, focal length, setting, proximity to subject, lighting, lighting type, framing, composition, etc. And that difference is exacerbated for split level (over/under) work.
See examples below by Pros Paul Toma and John Starret. The images below all use the smaller Outex Dome 120mm.
Dome lenses are ideally suited for wide-angle lenses. As with most things photography, there's no line or cut-off number. Everything is on a spectrum. In general, we mean focal lengths below 24mm , which are ideal for a number of reasons related not just to optics, but water, such as clarity, white balance, lighting, etc. We’ll explain each in more detail below.
Split Level (Over/Under) Focus
Because of many of the differences already highlighted above, there are complexities in defining focus on split level (over/under) images. By definition optical properties over the two mediums are different, so the camera operator can use the gear to help her decide how to create the image based on desired outcomes. The two images below highlight the differences. Both taken with Canon 6D full frame camera and Sigma 12-24mm f/4 lens. The 1st using the Dome 120mm, and the 2nd with the Dome 180mm.
Most of the settings, including depth of field, composition, framing, etc are similar, and both focal points are positioned (on "M" manual settings) to be underwater, lighting and the larger dome greatly assist in maintaining greater focal "parity" above and below water level.
Depth of field is critical tool in modulating over & under parity if that's the desired result. Use it accordingly. But over and under disparity can also be used to your advantage. In the example below the disparity between the two water levels only helps the author illustrate the story being told in the photo.
Refraction; Image is not as magnified due to the refraction of light in the water. Refraction is the visual bending that results from the change in density and therefore changes in light speed as it crosses from air to water. Refraction occurs when the light changes speed when it enters a body of water, causing it to change direction. The subject becomes ¼ closer and 1/3 bigger. See the pencil image below.
(Canon 16-35mm lens using Outex regular lens 82mm by Satiro Sodre)
(Canon 15mm lens using Outex Dome 100mm by Julie Thies)
Note again the excellent results with both the regular lens as well as the dome port photos above.
Sharpness & Chromatic Aberration
Another benefit of domes in water is improved color and sharpness retention since you can be closer to the subject and therefore create less distortion. Flat lenses create a progressive distortion away from the center of the image as they do not address the progressive refraction near the edges. That also means a dome port makes it easier to find focus throughout the frame. Similarly, it reduces
chromatic aberration (color fringing), as the same refraction impacts not only light but color, as the light separates into the spectrum’s component colors away from center. Dome ports help correct light dissipation over distance, helping ensure a more evenly sharp, focused, and color-correct image.
Outex dome ports come pre-packaged in a neoprene protective case to help store and protect them.
In this section, I want to discuss how to get good results with rectilinear wide-angle lenses, which means any wide-angle lens that is not a fisheye lens. Many people have had difficulty in this area. I’ll start off with a discussion on diopters, dome port optics, and the virtual image.
The first concept that I want to explain is the virtual image.
A lens behind a dome port does not focus on the subject, like it does on land; it focuses on a “virtual image” that usually lies 9-12 inches in front of the port, depending on the port size. The larger the dome port, the further away the virtual image is. If you need help understanding the virtual image concept, there is a tutorial at the bottom of this page.
One rule of thumb says the image of an object that is far away will lie approximately 1.5 times the dome diameter (or 3 times the radius) away from the dome port. (Source: scubageek). Objects that are closer than infinity (e.g. - not very far away) will have a virtual image that is closer to the dome port than 1.5x the dome diameter.
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Because of the "virtual image", don't manually set the focus of your wide-angle lens on the surface to the hyperfocal distance, like you would for a landscape photograph. To shoot in manual focus underwater, focus on an object that is 3ft away once you are underwater, switch to manual focus, and then change your f-stop (set a small enough aperture) until objects far away have acceptable focus. If you need to pre-focus above water, set the focus on an object 1ft away from the dome port. These distances are approximate, and should be tested with your setup.
Lenses that don't focus close, like the nikon 12-24mm, or nikon 17-35mm will require a diopter when used behind a dome port, to enable the lens to focus on the “virtual image”. Many beginners attempt to use wide-angle lenses without diopters, and then wonder why the edges are blurry. These lenses will generally work better behind larger dome ports.
Some lenses will still work without a diopter, but will have better sharpness with the diopter, although you can no longer focus to infinity. In fact, most rectilinear wide-angle lenses will benefit from a diopter. With a +2 diopter, which is not a strong diopter, you will still have a good enough range of focus. The Canon 17-40mm and 16-35mm lenses fall into this category.
Lenses that focus ten inches away or closer like the Sigma 10-20mm or Nikon 10-24mm generally don't need a diopter, especially when using an 8-inch dome port or larger.
Diopters are commonly called close up lenses. The housing manufacturer or housing dealer can usually recommend the proper extension/diopter combination for your dome port and lens. Usually a +2,+3, or +4 diopter is recommended. “+2” refers to the strength of the diopter, with +4 being stronger than +2. A +4 diopter is the strength most often recommended with a wide-angle lens that does not focus within 12 inches of the dome port.
Some people say you should avoid Tiffen diopters, and get a Hoya, or even better, a B&W diopter. The B&W diopters are highly rated. Search for “close up” and lens when looking for diopters on line. Fisheye lenses generally do not take or need diopters.
The further away the close-focusing distance is for a lens, the greater need it will have for a diopter
The smaller the dome, the greater the need for a diopter, because the "virtual image" lies closer to the dome. Note that domes of similar size can have different amounts of "curvature" which can also affect performance and corner sharpness.
Many wide-angle lenses will perform well in large "super-domes" that are 9 inches wide, even without diopters.
Some lenses that already focus very close can even work in small dome ports, which are less expensive, lighter, have less drag, and can make shots taken on the bottom easier.
When using a wide-angle lenses, especially rectilinear lens, such as the Nikon 12-24mm or Canon 10-22mm lens, care must be taken to get optimal results. By optimal results, I mean acceptable sharpness in the corners of your image.
For the best results:
Align the base of dome port with the 1st (most outer) element of the lens by using the appropriate extension ring. However, its not always easy to tell where the lens elements are. Check with your housing manufacturer for the best alignment.
You can use ports made out of optical glass or acrylic. Optical glass is more expensive, but much more scratch resistant than acrylic, and water falls off it much easier if you are doing over-under shots. Some people think image quality & contrast may be improved with a glass port, while others feel that the difference is not noticeable.
Use an 8-10 inch dome port if you are using a rectilinear lens. I have not seen a significant difference between small and large dome ports with fisheye lenses.
Performance is often best at smaller apertures, and some people stop down to at least F8 or smaller with some lenses. Use a higher ISO, for example ISO 400, if necessary to use these small apertures.
Many rectilinear lenses will have improved performance with a +2 or +4 diopter. Fisheye lenses do not benefit from a diopter. If your wide-angle lens has a fairly close minimum focusing distance, and your dome port is large enough, you probably will not need a diopter.
Test various port extension / diopter combinations in the pool to find out the best combination for your housing & lens combination, or discuss this with your underwater housing dealer or shop or housing manufacturer.
If you are using a compact camera - e.g. a Canon G12 or S95, you will probably have to use macro mode with a dome port or your photos will be out of focus, because the virtual image lies close to the dome port.
Angel shark photo taken with my tokina 10-17mm fisheye lens at 14mm, acrylic S&S 6 inch dome port. F13, 1/160th, ISO 160, strobes out wide. I shot at F13 to ensure a sharp photo in the corners and rear of the fish. The shark was very close to me, maybe 2ft away.
Glass ports are heavier, cost more but are more resistant to scratches.
Because glass dome ports are heavier, some underwater photographers like the effect it has on the underwater buoyancy of their setup - meaning the port won't "float up". However, it depends on the housing.
It is possible to "mesh out" minor scratches in acrylic ports. Read how to remove the scratches on the underwater housing maintenance page.
Glass ports can supposedly shed water easier for over-under shots.
Some people believe a high-quality well built glass port will have better optics. In my pool tests between a Sea & Sea 6 inch glass and acrylic ports, I could not tell any difference in sharpness, color or contrast. Of course these test results are valid only for these ports in the conditions I tested them in. Here are the dome port pool test results.
Small dome ports versus larger dome ports
Larger dome ports will usually be heavier and more expensive.
It's much easier to take CFWA photographs with smaller ports.
At wider apertures (larger F-stops), corners will be sharper in a larger dome port. However, this difference can be small with fisheye lenses. See my sea & sea dome port tests.
There are some differences with over-under shots.
Wide Angle conversion ports are newer ports developed by Nauticam that are a combination between a lens and a port. These conversion ports have lens elements on the front, but they are also a port in that they house the lens and provide water tightness to the system. Known as Nauticam WACP for short, they are not wet wide angle lenses.
Wide angle conversion ports are the best option if you want the best underwater wide angle optics available with a rectilinear wide angle lens. These ports are capable of producing some of the widest rectilinear wide angle fields of view possible. Wide angle conversion ports also allow for "through the lens focusing" and water contact optics. This means the lens is actually focusing on the subjects in the water rather than the virtual image. This results in sharp corners, even with a rectilinear lens underwater. However, all of these benefits come at a price. Wide angle conversion ports are some of the most expensive wide angle options on the market.
The two available wide angle conversion ports currently are the Nauticam WACP-1 and the Nauticam WACP-2. The WACP-1 is designed for 28mm equivalent lenses and can produce a 130 degree field of view. The WACP-2 is designed for 14 mm equivalent lenses (and closer) and can produce a 140 degree field of view - the widest field of view possible from a rectilinear wide angle lens.
Please see the composition section for more info on wide-angle photography. (Ambient light and silhouetes underwater, CFWA, wreck photography), or read the wide-angle interview.
For strobe positioning, see the strobe position section.
For camera settings, see the macro and wide-angle settings section.
For lens selection, read about the best underwater lenses
There’s also some excellent reading on dome port optics here: http://scubageek.com and some additional reading on Paul Kay's site here.
I'm going to emphasize this again, because it comes up over and over. When you use a fisheye or rectilinear wide angle lens in a dome port, people seem concerned with whether it fits, or vignettes at all. Both of these are important, (having a lens hit the inside of your dome port is not fun), but you must also realize that getting the correct port extension is also important, even with fisheye lenses. Don't always think everything is ok just because the lens fits in the port.
In zoom lenses, the optimal location of the dome port often changes as the lens zooms in and out, so people often optimize for the lens at its widest setting.
The virtual image concept can be hard to grasp. Basically, underwater the camera "sees" the image much closer than it really is, because of the optics of the dome port in water. Your camera auto-focus will still work correctly - it is just focusing on this "fake" image (but real to your camera sensor) closer than you think. You will notice this if (1) - you manaully focus your wide-angle lens to an image 5ft away topside, leave in in manual focus, and then go underwater. A photo of something 5ft away will then be blurry, because the virtual image underwater is much closer than 5ft. This is why you should never pre-focus a wide-angle lens on land that you are going to use underwater.
Or (2) you use a wide-angle lens underwater that does not have close-focus capability. Your shots will be a little blurry, and a diopter will be needed with this lens.
I hope this helps! Please ask if you have more questions.
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