CameraCrazy

Singh-Ray came out with a great filter called the Vari-ND. This is a variable neutral density filter and works similarly like a circular polarizing filter, you can turn a dial on the filter and it varies the amount of light allowed into your camera.

The Vari-ND does a very impressive 2 to 8 stops of light allowing photographers to shoot long exposures in bright light. In essence it allows photographers to combine different apertures, shutter speeds and even ISO’s in all types of brightness while still achieving correct exposure.

This truly is a great filter, no longer do you need to purchase two or three separate ND filters and stack them to minimize a discrete amount of light. Instead, you can now just use one filter and since it’s variable there are no discrete amounts your stuck using, you can turn the ring to achieve any stop (including fractions of stops).

About the only thing going against the Vari-ND is the cost, with a price tag of $350 I imagine only the professionals who make a living out of photography could justify spending that much on a filter.

This started me wondering how they did it? After contemplating it for a few days I eventually thought back to one of those stupid moments in photography that I was glad no one was around to witness. I was new into photography and had just purchased my first polarizing filter. I headed out to the mountains and found a picturesque lake and a sunny blue sky. I had on my clip-on sunglasses because it was such a bright day, I excitedly screwed the polarizer on to my lens, setup my tripod and began setting up my shot. I looked through the lens and all I saw was black, “I must have forgot to take off my lens cap” I remarked to myself, but when I checked, sure enough the cap was off. Well this started me to panic, “something must be wrong with my camera, lens, both?” I took the lens off and checked my camera and lens for quite some time, they didn’t seem broken, but every time I put the lens back on and looked through, nothing but black. After about 30 minutes of an in-depth assessment of my camera gear, swearing and even more swearing I looked through once more. This time however my head was tilted, suddenly I could see through, it was dark, but at least I could see something. When I tilted my head to the original position, it went back to black, then I tilted again even more and the picture got brighter. I suddenly realized and felt quite stupid that my clip-on sunglasses were polarized and I was looking through my lens with a polarizer attached.

Polarizers work by filtering light and allowing only light through in a particular direction. If you stack two polarizers together they will still let light through provided they are both lined up to allowing light through in the same direction. If you turn the polarizers 90° to each other, the light allowed through by the first polarizer will be blocked by the second filter (because it’s a different direction), light will not proceed and you will only see black. If you turn the second polarizer to an arbitrary angle (45°, 60°) you can vary the amount of light that passes through.

What does this have to do with the Vari-ND, well this story is the basis of how I think a Vari-ND can be created. My hunch is that the Vari-ND can be made using a circular and linear polarizer (finally a use for a linear polarizer!). Take a look at the photos inset in this post, sure they’re terribly done, but the effect is what’s important! The pictures are from a circular polarizer on my lens and my clip-on sunglasses (a linear polarizer). In one picture you can see through right through the clip-ons, but as you turn the dial on the circular polarizer and begin to change what light can pass through you reduce the amount of light that can pass to the camera. When the circular polarizer is turned so its perpendicular to the linear polarizer (90°) no light can pass and you are left with black.

Polarizer and Clip-ons at 0° (same direction)

Polarizer and Clip-ons at 45°

Polarizer and Clip-ons at 90° (perpendicular direction)

This is why I think the variable neutral density filter will work, by turning the circular polarizer, you are allowing a certain proportion of light through, hence adding or subtracting stops needed for proper exposure. And since polarizing filters are already neutral color, there are no color casts or unwanted effects. So here is the experiment: To make your own variable neutral density filter all you need is a circular polarizer (chances are you likely already own one) and linear polarizer, of the same size (so they can screw together). If you don’t have the same size filters, then a stepping ring(s) can be used. That’s all it takes. Attach the polarizers together and put it on your camera. If my thinking is correct, you should now have an affordable variable neutral density filter.

So does it work? Well, I actually don’t know I haven’t had the opportunity to purchase a linear polarizer yet. If it does work, the biggest issue I see with it is that since your camera is now looking through a linear polarizer, you may not be able to rely on auto-focus, particularly in modern cameras. If this is so, you would have to switch to manual for focusing. I don’t think this is a big problem since most photographers who stop down appreciable amounts are likely using the camera on manual already.

A request from you: I’m anxious to know if this really works, so if you try this out, I would be very interested in knowing how well it worked. So drop me a line describing your experience.