Uploaded 30. Oct. 2010

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Photographers are often concerned about retaining a fast enough shutter speed. Whether you want to catch a bird on the wing, freeze the movement of a running cheetah or just prevent camera shake in a low-light situation – you want your exposure time to be very short to avoid blurry images. Nevertheless, a bit of a blur can sometimes be quite desirable; landscape pictures with blurred water movement are a great example. Rather than freezing the motion of each little wave and droplet with a short shutter speed, a longer exposure time transforms the water to a smoothly blurred surface.

With an exposure time of 30 sec. & f12, the water movement of this small creek gets evenly blurred. Germany 2010

In order to achieve a long exposure time, you want to close your aperture (high f-number) and choose a low (i.e. non-sensitive) ISO speed. But even in a dim-lit environment like the woodland creek displayed above, this is often not enough to allow an exposure of several seconds.
That’s where grey filters come in. Grey filters or ND filters (meaning neutral density) consist of coated glass or epoxy resin and can usually be screwed on to the front element of your lens. These filters block a big proportion of the available light which results in a longer exposure time, enabling photographers to get the intended motion blur. ND filters are available in various versions: ND 2 filters will transmit just 1%, ND 4 filters 0.01% and ND 6 filters only 0.0001% of the light available.

But sometimes even such ND filters are not dark enough and since they can also be quite expensive, here’s an easy and cheap do-it-yourself option: use a welding glass.

Welding glasses are normally used in welding helmets for metal processing: they are protecting the worker's eyes from the ultra-bright light of the welding flame. Because of this, welding glasses are very restrictive, blocking the vast majority of light. Moreover, they are very cheap and you can get them in almost every hardware store or via Amazon.

So we bought two different welding glasses, a very opaque and an even darker one. Since we wanted to be able to easily screw the filters on our lenses, we also bought some adapter-rings (77mm and 67mm step-down rings from enjoyyourcamera.com). We then just glued the filters onto the glass using household-glue (Uhu Alleskleber). You want to make sure that there's no light leaking in from between the glass and the filter, otherwise the filter has no effect.

With this setup, we can now take long-time exposures during the mid of the day. But as for all long time exposures, prevention of camera shake is crucial – usage of a tripod is therefore mandatory. A remote control cable-release can also help keeping your camera steady, but a self-timer combined with mirror lockup does the job as well.

Due to the fact that such grey filters block the bulk of available light, your viewfinder is going to be very dark indeed and the AF of your camera won’t work. But for landscape photography, using manual focus is not an issue. You can also first compose your image normally using AF, then screw on the grey filter and take pictures.

Another woodland creek. 40 sec. exposure time, f9. Germany 2010

Since welding glasses are not originally designed for photographic use, their colour reproduction is far from neutral: our copies display quite a greenish tint. However, this can be fixed easily either during post-processing or by using a manually set white-balance. My preferred method is first taking a (greenish) picture and then just use that image as a reference for your manual white-balance (check your camera’s manual for the exact procedure).

Grey filters in use. Simple rubber-band version (left) and screw-on mount (right).

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