Focusing Panoramic CamerasBy Ethan Ace, Published May 05, 2013, 12:00am EDT
Focusing panoramic cameras is really important. Indeed, after testing 9 different panoramic cameras across many manufacturers, we believe this must be done manually for each camera. This might seem unnecessary as panoramic cameras are, after all, fixed focal lenses. However, though all the cameras in our tests shipped focused by the factory (with the exception of ImmerVision, sold as an accessory), we found it necessary to refocus nearly every one to maximize image quality.
Since panoramic cameras have lower pixel density by nature, due to their wide FOV, fine focus issues may be difficult to spot. Worse, because of the FOV, even being slightly out of focus will have a large negative impact on image quality. For these reasons, we recommend users always refocus panoramic cameras.
Panoramic Camera Focus Overview
The specific mechanism by which panoramic cameras are focused varies from camera to camera. However, standard features for different form factors exist:
- In box style cameras, focusing is performed much the same as with a standard non-fisheye lens, by turning a focus ring and/or iris ring (for manual iris lenses). ImmerVision also includes set screws for centering the lens of the camera imager, a feature not found in other lenses.
- In minidome cameras, focus is typically performed by turning the lens. Some models, such as the Axis M3007 attach a ring to the lens to make focusing easier, while others require turning the small lens directly. Some may also include special tools which are required to turn the lens for focusing, and may not be focused by hand.
Some cameras include a gimbal mount to account for off-level surfaces, as well. We look at all of these features in this screencast:
The focus procedure for fisheye cameras varies slightly from traditional cameras. These are the key points to remember:
- Dewarp for focusing: We recommend not focusing using the warped fisheye overview, but instead using a dewarped view, preferably the view style which will normally be used (dewarped, quad, panorama, etc.). Users may find it necessary to focus from the fisheye view on occasion. We found it easier to focus some 5 and 10 megapixel cameras in the web interface, for example, because their high resolution was causing some frame drop which made fine focusing difficult.
- Focus edges: It is important to focus using a target closer to the edge of the image, since this area suffers from the greatest reduction in resolution due to dewarping.
- Focus center: Though a target at the edge should be used for focusing, we recommend using a target closer to center as well, and adjusting focus if need be. We found in some cases that focus had to be adjusted somewhere in between the two to produce the best all around image.
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