1/11/2024 0 Comments Nikon fxLens and dome selection is important, but in many cases setting them up right also makes a huge performance difference. Hence, although the curve of the virtual image will be less, these domes are typically smaller in diameter so the image will be closer to the lens and it still may not be able to focus.Ī less curved dome may help the camera deal with DOF issues in the corners by “flattening” the virtual image.Īnything that effects the distance between the lens’s optical elements and the virtual image will effect the ability of the lens to deal with the curved and close virtual image. Whilst this can help reduce the curvature, it is important to remember that the diameter of the port determines the position of the virtual image. It is possible to use a “less curved” dome to try and reduce the curvature of the dome, Typically, they are actually sections of a large dome cut down. This diagram (courtesy of Alex Mustard) shows the relation ship between the distance of the virtual image from the lens versus dome port diameter. Hence, larger domes tend to also produce a less curved virtual image than a smaller dome as the lens only “sees” the center and hence less curved part of the dome. Given that most domes are spherical, the amount of curvature is hence more as it approached the edges of the dome than it is in the center. Optical theory says that larger domes generate a virtual image that is further from the lens. The first of these is the diameter of the dome and secondly, linked directly to this, is the curvature of the dome. Given that this compromise exists, there are additional factors that affect corner sharpness. In addition, the camera’s viewfinder does not show a DOF preview, so it cannot be seen until the picture has been taken. The center is normally in focus, as the autofocus points tends to be concentrated around the center of the sensor, so it is the corners that suffer. DOF is controlled by aperture, and the smaller the aperture, the greater the depth of field. Hence people will often describe an image as having soft corners, effectively saying that the lens and dome combination did not have sufficient DOF to get both the center portion and the corners in focus. As the virtual image is not flat, but is being recorded onto the flat sensor’s surface, it can be difficult for there to be sufficient depth of field to allow for the “closer” corners and the “further away” center of the image to both be in focus.Ĭameras with large sensors have a considerably less inherent depth of field (DOF) than smaller ones.The lens must focus on this virtual image (rather than the actual scene), which means that it must be capable of very close focus.As the dome is curved, so too are the corners of the virtual image. This virtual images is what is actually captured onto the camera’s sensor. When a lens is placed behind a dome, and the dome is then immersed in water, the dome generates a virtual image just in front of the port itself. In order to understand why, it is important to understand a little bit of dome port theory. Finding rectilinear wide-angle lenses for full-frame Nikon SLR cameras that work well underwater is a challenge.
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