It is necessary to add a polarizing filter of 3 f stops equivalent density ( or a neutral density filter, ) and this requires an adapter which extends the lens housing beyond the most extreme travel of the zoom lens.
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The neutral density filter permits effects requiring wide apertures or long exposures to be applied to brightly lit scenes, while the graduated neutral density filter is useful in situations where the scene's dynamic range exceeds the capability of the sensor.
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:A graduated neutral density filter can help digital cameras with a restricted dynamic range cope with a bright sky etc . If the sky gets burnt out, then no amount of post editing of the RAW file will bring it back.
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It is also important to note that even at 4.5 %, ( ~ N . D . 1.35 ) the light from the sun is still strong enough to burn the retina, and so an appropriate neutral density filter must still be used.
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Simple neutral density filters are also common as they can cut down the amount of light reaching the eye by 60 95 %, something that is helpful especially when observing a full or gibbous moon so the surface does not appear as washed out.
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If light levels are high the use of neutral density filters will reduce the light entering the setting to the lowest available on the camera ( commonly 100 ), as this reduces the camera's sensitivity to light and so gives the slowest possible shutter speed.
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However, as long as a sufficiently short exposure time is available, it is possible to exactly mimic the effect of a graduated neutral density filter by using two exposures of the same scene one or several stops apart and blending them with a graduated mask in an image editor.
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A film frame that is exposed for 15 seconds will receive 750 times more light than its 1 / 50th of a second counterpart . ( Thus it will be more than 9 stops over normal exposure . ) A scientific grade neutral density filter can be used to compensate for the over-exposure.
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When a neutral density filter ( a darkened lens typically gray ) is placed in front of, say, the right eye, the pendulum seems to take on an elliptical orbit, appearing closer as it swings toward the right and farther as it swings toward the left, so that if it were to theoretically be viewed from above, it would appear to be revolving counterclockwise.
