I love trying new things. It’s a failing, really, as new things often win over old things in the short term and I find it hard to maintain enthusiasm unless I really get hooked. Yesterday, though the letter box came a small package with my latest toy – a 10 stop neutral density filter.

Not everyone’s idea of an exciting thing, and in the world of photography it’s almost ancient history, but at the bargain price I got it for, it was well worth the money for me to add another technique to the collection – you can always learn something and I love learning about photography. What does a 10 stop neutral density filter do, I hear you ask (or was it a yawn)?

Neutral density filters block light evenly across the spectrum. That might sound counter intuitive for photography, where the aim is to record the light, but in some circumstances there can be too much light. If you are trying to use a large aperture to throw a background out of focus, it can often be too bright to be able to open up enough to achieve that effect (particularly with smaller sensors, where there is a struggle to get small depths of field). A neutral density filter will help in managing the light levels. They can also be used to force a slower shutter speed and this means that movement can be recorded as a blur. The classic example, and one you’ll have seen to excess on this blog, is the blurring of the movement of water until it becomes silky smooth.   You can see examples here and here and here.

The strength of a neutral density filter is measured in a variety of ways but they all attenuate the light by fixed amounts, referred to as stops. Originally, a stop was the name of the piece of metal with a hole drilled in it that went between the lens and the film of early cameras to control the light levels. it ‘stopped’ the light. Later, variable aperture holes were used and most modern lenses have these. A filter might be rated ‘x2’, or ‘0.3’ and reduce the amount of light hitting the sensor by 1 stop. the equivalent of doubling the shutter speed or halving the size of the aperture. I’ve been using 2 and 3 stop filters (x4 and x8 or 0.6 and 0.9) for a while to get the smoothed water effect. The new filter has a significant increase in density and appears opaque unless you are staring at a strong light source.

The extreme effect this produces allows me to record the passage of time by making it possible to keep the shutter open for extended periods of time. While fast shutter speeds and high speed flash stops motion that would otherwise be invisible, so the 10 stop filter captures movement that is too small or too slow to be easily seen.

All that is fine in theory. Today was my first opportunity to try the filter out and Rufus volunteered to accompany me to the River Tawe, where I wanted to not only catch movement in the water but also in the clouds. I had an image of both sky and foreground being blurry with movement, and only the rocks in the water being sharp. Brief experiments in the garden yesterday showed that at such high density, the camera was unable to meter effectively and so I’d experimented to find a reasonable starting point with exposure compensation. It is recommended that after taking an initial reading without the filter, that you calculate and set the corrected shutter speed and aperture manually.

We got to a chilly and windy river just as black clouds were gathering ahead. While Rufus splashed about, oblivious to the wind and temperature, I set the camera up on its tripod and set about calculating the correct exposure. It was in the order of 60 seconds, so I set the camera off. Within 20 seconds, the drizzle started, and it was quite thick. Cutting the exposure short, Rufus and I dived for the car (which wasn’t too far away). After 5 minutes, it cleared up, so off I went again to a different part of the river. It took a while to set up and I was concentrating so much that I didn’t see the rain clouds gathering. I set the camera going for another 60 second exposure and… rain!

Today’s test of the filter clearly wasn’t meant to be, so after a few more minutes with no sign of the rain stopping, we gave up and drove off. Rufus had his walk in the woods near the upper Lliw reservoir, where the drizzle didn’t quite get through the canopy of leaves.

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