Image distortion caused by camera in cylindrical tube So the inspiration of this issue actually comes from an engineering point of view. The jist of the project is that I need a water proof enclosure to fit a camera in alongside other electronic components. The easiest available enclosure for my use case is an acrylic cylinder. I want to know if there is a way I can predict what kind of distortion I will get in images taken by the camera in the tube and if there is a physical way to correct for this distortion. The assumption here is that camera will always take pictures perpendicular to the cylindrical axis of the tube. Is there a way I can attach more acrylic inside and outside to limit the distortion.
Any advice or guidance is appreciated. Even a reference to where I can get started studying this issue would be welcome.
 A: I would start by taking a picture of a calibrated target (like a sheet of graph paper) using the camera and some of the tube cut in half.  You'll get  a good idea if the distortion is significant.  If it is you'll need to do a geometric correction in software.
A: Photographing through glass can be tricky, there's the need for polarizing filters and the inability to use flash, adding to that a curved surface only makes it more difficult.
You haven't said why you want a waterproof enclosure, is it simply for rain or immersion in water; and at what pressure or depth. The easiest and cheapest solution is to keep the camera in your home and shoot out the window, even that isn't without it's problems.
I'll assume you want the camera outdoors.
If you can buy an inexpensive nano sized fishtank and turn it upside down that will be a simple rain proof solution, the gear still needs to withstand the moisture in the air.


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*If you have air on both sides of the glass then refraction won't be a problem if the acrylic is optical quality, if it isn't (and usually it isn't) you'll have distortion that you'll have to calibrate for.

*If you're going to have water on one side of the glass and air on the other you will have problems with refraction. The HydroOptix website shows their underwater scuba diving masks that correct for the distortion.

Usually you'll use a dome port for underwater photography. There's a large number of articles about underwater photography and optics on the ScubaGeek website. Here are some points to remember, from the article: "Dome Port Optics and Diopters for Wide-Angle Lenses" by Scott Gietler of the Underwater Photography Guide website:


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*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.

*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.

*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.

*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.


*The third situation is where you have a camera in an airtight container, underwater, and you want to take pictures out of water. I believe that is beyond the scope of your question but for completeness I'll refer the interested reader to the video: "Stella Maris: Stellar Marine Refractive Imaging Sensor". The problems are two refraction components and surface waves add to create a moving distorted surface that needs to be corrected for. For more information see their article: "An Airborne Virtual Periscope".
See also: 
NASA's Technical Report: "Evaluation of lens distortion errors using an underwater camera system for video-based motion analysis".
Tru-Vue's website featuring AR coated optical quality acrylic.
