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Our on-line Knowledge Base contains answers to some of the most common support questions. It has information about all PGR products and was developed to help customers resolve product issues. It is constantly updated, expanded, and refined to ensure that our customers have access to the latest information.

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Why is my image darker in the corners?
Article 87: Why is my image darker in the corners?

SUMMARY:
A darkening of the corners of an image relative to its center is likely a result of vignetting. This article describes vignetting and potential remedies.

APPLICABLE PRODUCTS :
All Imaging Products • 

ANSWER:

A darkening of the corners of an image relative to its center (see example below) is likely a result of vignetting, which is an expected effect with many lenses. There are different types of vignetting, including optical, natural, and mechanical vignetting. For a good summary of vignetting go to http://www.vanwalree.com/optics/vignetting.html#optical.



One way to reduce or eliminate this effect is to buy a better lens, such as a C- or CS-mount lens. You can get these from companies such as Pentax, Fujinon, Computar and Edmund Optics. Another option is to buy a larger format lens. For example, if you are using a Dragonfly, which uses a 1/3" CCD, a lens built for a 2/3" CCD might reduce this effect. However, be aware that focal lengths can differ significntly between different lens formats.

Some PGR Imaging Products, such as the Dragonfly, Dragonfly EXPRESS, Firefly and Firefly2, allow for microlens and C/CS-mount lens holders that can be mounted to the bare printed circuit board (PCB). The imaging sensor is centered relative to the 2 mounting holes for these lens holders. These holes allow for some small adjustments in where the lens holder sits relative to the sensor. If you are seeing vignetting primarily on one side of the image, it may be possible to reposition the lens holder to reduce this effect.

The above products can also be enclosed in an optional aluminum case enclosure (CSBOX). Similar to what was described above, when assembling this case and the PCB there is a small amount of movement in the position of the PCB relative to the case. For example, if there is distinct vignetting only on the left side of the image, try unscrewing the PCB from the case, push the PCB farther to the opposite side, and screw the board back down.



RELATED ARTICLES :
KB Article 28: Dragonfly and Firefly2 lens holder format
KB Article 31: Microlens specifications for Dragonfly and Firefly camera series.
KB Article 88: Vertical bleeding or smearing from a saturated portion of an image.
KB Article 98: Understanding flange back distance on C-mount and CS-mount cameras.


ARTICLE INFO:
Article ID:
87
Published:
12:00:00 AM
Last Modified:
3/4/2005 10:30:33 AM
Keywords:
vignetting, dark corners
Issue Type:
Error



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