Cross star filter in photography
Cross star filter used in photography gives an effect, emanating 'beams' of light coming out from a point source of light, or a bright object in the photograph. Generic term for this filter is crosstar, and the number of 'beams' coming out from the source of light could be anything from two to sixteen.
This filter is a plain glass, with parallel indent lines on it. Second series of lines at ninety degree angle will give a cross-star, which has four beams. If the angle of lines is at sixty degree, it forms an equilateral triangle and it will produce a star with six beams.
The intensity, contrast, size and shape of the star, which is produced because of this filter, will depend on the aperture we use and the brightness and contrast of source of light, present in the photograph. Wide aperture will produce a wide and long star with low contrast and less defined shape. As we stop down for a smaller aperture, a star produced by the filter will have more defined shape and contrast will increase.
Below is a photograph, without a cross star filter. It looks just ordinary snap shot.
Above is the effect generated with a cross star.
Some filters are available with two different glasses, which can be rotated independently to produce a four beam star, which is not having an intersection at right angle. They are vari-cross angle filters. With this filter, we can change the angle between two beams.
Cross star as a filter, does not have any filter factor, so they does not require any compensation on the exposure. They can be used in series to produce a creative effect. However, be sure for the quality of the filter for its optics and optical coating. As we have to include a light source in the composition to get the effect, poor quality filter with no coating will produce a flare. Use a good lens hood to minimize any possibility of entering unwanted light, outside the composition, in the picture.
Many digital cameras provide an in-built photo editing software, where we can add a cross star filter effect without using a filter, even after shooting. Shoot a picture in a normal way and then go in the 'edit' mode to add a star effect. Some software of a camera may give options on number of beams we can create and the intensity of the star burst. The edited photograph will be saved as a different file. Otherwise, photo editing software in our computer also can be used to add this effect, where actual control of feel is completely in our hand.
Use this filter to add some drama in night photography.
Read more about other filters used in photography:
Color correction filters: Optical filters for correcting colors in photographs
Filters for black and white: Use of cpmplementary color filters in black and white photography
Neutral density filters: Filters for reducing the brightness of light
Polarizing filter: Filter to cut off unwanted reflections in the image
Soft focus filter: Use of soft focus filter to add misty look and to remove unwanted texture
UV filter: Ultra violet and sky light filters for removing UV radiation and blue cast
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