Singh-Ray Vari-ND

Singh-Ray Vari-ND

The Singh-Ray Vari-ND is, as it's name suggests, a variable neutral density filter. A neutral density filter (ND, sometimes also called a "grey filter") simply absorbs light while ideally not introducing any shift in colour or other undesirable effects -- it should only make the scene darker.

When things get darker, one has the option of opening up the aperture and/or making the exposure longer to maintain correct exposure. With digital cameras one might also increase the amplification of the sensor (the ISO number, "sensitivity") but the only effect would be to increase the noise ("graininess") in the image.

Opening up the aperture (= setting a smaller aperture number) reduces the depth-of-field (DOF) so that creative use of sharpness becomes possible. With an ND-filter, this is then possible even in bright lighting conditions (which would otherwise require a small aperture to obtain correct exposure). In very bright conditions, frequently encountered in Namibia, one might also want to open up the aperture to reduce diffraction (applies to very small apertures like f 22 and smaller) or to get to the sweet spot of a lens (each particular lens is sharpest at a particular aperture, usually around f 8).

Making the exposure time longer allows creative blur, e.g., motion blur due to a moving animal or trees or, of course, water. Using a long exposure time is the primary means of showing motion in an image. Again, with an ND-filter, this now becomes possible also in bright lighting conditions.

Now for the "Vari": Normal ND-filters come in fixed densities of, e.g., 1, 2 and 4 stops, meaning that they require to open up the aperture by 1, 2, 4 stops, respectively (or to equivalently increase the exposure time by the respective number of steps). It is the same to say that 1/2, 1/4 and 1/8, respectively, of the light in the scene reaches the sensor. Obviously, different lighting situations and different creative aims require a whole set of these filters. The Singh-Ray Vari-ND, as far as I know, is the only ND-filter that can be continuously adjusted from a nominal 2 to 8 stops, making it unnecessary to carry a whole set of filters. It's effective range is from about 1.5 stops to about 10 stops. Very useful!

The filter is not fool-proof, however: Especially at higher densities, the in-camera exposure meter gets confused -- bracket (i.e., make a series of images with under- and over-exposures from what the meter says) and / or use your cameras preview/histogram function. Don't forget to cover your camera's eyepiece as light enters through here as well! The filter works best at small densities, at high densities (especially above 8 stops) results become unpredictable and a cross-bar effect might show (see later). How strong these artefacts will be depends also on your sensor and lens. I have noted a general shift towards warmer colours. Also be careful about vignetting due to the filter's mount, use the slim version for wide angle.

The mouse-over image below shows a comparison between no filter (Canon EOS 20D, ISO 100, f 5.6 at 1/500 sec) and using the Vari-ND at a density of about 2 stops (i.e. at f 5.6, 1/125 sec). There is a shift towards warm tones (look especially at the sky; both images were taken and processed with the same settings). Note there is no polarisation effect (sky doesn't get darker, reflections on lake stay the same; nevertheless, the Vari-ND cannot be used in combination with a polariser).

Below is a little pop-up gallery showing the effect of the Vari-ND at increasing densities. These images were made with an 18 mm wide angle lens. I'll do a similar test with a long lens once I have time. Note that the slowest time achievable (using f5.6) is about 1/2 sec. Setting a smaller aperture would thus lead to exposure times quite sufficient to produce strong motion blur under these average lighting conditions. I didn't cover the eye piece, remind me to do that next time. The images are straight from the camera, i.e., no contrast enhancement etc. and no correction of vignetting.

Click here to view the gallery (pop-up)

OK, here is another gallery that actually demonstrates motion blur... This sequence was shot with the sun behind me as opposed to the previous one where the sun was at 90 degrees. Just to show that there really is no polarisation effect. Also, this sequence was shot at f16, more realistic for landscape photography. The effect is quite similar, only this time the camera exposure meter gets really confused (last image, see remedy below). Same lens and processing as above.

Click here to view the gallery (pop-up)

I recommend to use it in practice like this: Mount filter and set to minimum absorption. Set camera to manual exposure. Compose and focus. Turn AF off. In manual exposure mode, if you know what aperture/shutter combination you want: Note exposure at minimum filter setting and desired aperture/shutter combination. Is this within the ~ 8 stops capability of the filter? If yes, rotate filter until exposure appers to be correct, then bracket. Otherwise, adjust your desired exposure settings. In Tv-mode: Set the time you desire, then proceed as above, additionally adjusting the aperture. NB: Bracketing may be achieved by simply rotating the filter!

The filter is not cheap (about US$ 350.- and up, depending on diameter and mount) but well worth considering, especially when space/weight is of concern.

I dropped mine into the Pacific once and so had to disassemble it to get rid of the salt in-between the two glasses. All I can say: Be very careful which glass goes where (front or back), which way it is oriented (which side faces outwards) and what the relative angular positioning between the glasses is (i.e. make sure you can reproduce the marker settings on the outer ring).

My experience with Singh-Ray is that they are friendly and helpful but sometimes have supplying difficulties.

As an alternative to all this a normal polariser might sometimes suffice. This is the case when polarisation is wanted anyway or when a polariser will have no effect besides darkening. This approach cannot be used when shooting a wide landscape with lots of blue sky (even worse: at 90 deg. to the sun) -- the sky will be darkened very unevenly due to a change in polarisation of the natural light over a large region of the sky. Experiment. Stacking two polarisers would, in theory, give you the same result. But in practice, adjustment of this stack of four glasses will be complicated and you will get reflections and vignetting. And it won't be any cheaper if you use good ones.

As you may have noticed above you can't turn bright daylight into midnight using the Vari-ND. Singh-Ray has therefore just announced the Mor-Slo 5 stops ND which can be used in combination with the Vari-ND, increasing the maximum range to about 13 stops.

Singh-Ray's Vari-ND page

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