I've been asked a few times now, how I manage to use graduated neutral density filters with my Mamiya 7II. So I thought it was about time I wrote an article about it to explain ND grads and how to place them on a range finder camera.
What the human eye sees, and what a camera see are two different things. The human eye is capable of capturing a dynamic range (brightness values from dark to light) that is wider than what a camera can capture. This is why often you will see a shot where the sky is burnt out while the ground is exposed correctly, or the sky is ok, but the ground is underexposed (almost black). Film and digital sensors cannot cope with such a difference in light values between the sky and ground, yet our eyes are able to handle this difference in contrast and make it appear to us as though the brightness is the same between the sky and the earth. In order to bring this contrast or 'latitude' down to a manageable level, so we can 'squeeze' the entire scene into the dynamic range that a camera can record, we use Neutral Density Filters. Neutral means that they do not affect the colour of the scene in any way, they simply darken down an area of the scene (typically the sky) so we can get a good exposure in camera. I use these all the time for landscape work.
With a rangefinder camera, you do not view your scene through the lens. In the case of the Mamiya 7II, the lens contains the shutter and so is permanently closed, until the moment of exposure. There is also no prism or mirror. Which means the camera is a lot more compact and more silent too. But the draw back is that you don't get to see what you'll get when you expose. Most range finders have a side window showing you an estimate of what you'll get with some dotted lines at the edges to compensate for different focal lengths.
Anyway, the problem with using ND filters on a range finder is that most folk think it's very hard to judge the correct placement in front of the lens.
Above are two Lee 0.9 (3-Stop) grad filters. The left hand one is a soft grad, while the right hand one is a hard grad filter (one of my most used grads). As you can see - the graduation of the hard grad is rather dramatic in the middle of the filter. Most folks think that placement needs to be precise, but to be honest with you - it doesn't. When you put something so close up in front of the lens, it becomes diffused. This means that the graduation effect of the hard grad becomes less pronounced. Unless you are really way off with your placement, you're not going to see a problem.
So how do I place the filter? Simple - I guess. If the scene I'm shooting has a sky that is using 1/3 of the area of the scene, then I place the filter roughly 1/3 of the way down. If the sky takes up 1/2 of the scene, then I simply place the filter half way. Etc, etc.
The other thing that I tend to do is take more than one shot of the same scene. If I'm uncertain about the filter placement, I'll take the scene a few times, each time with a subtle adjustment, moving it up or down by a few centimeters. But I've often found that it's been unnecessary.
My favourite ND Grads are made by Lee in the UK. I've tried others such as the Cokin system but found them not as effective. But they are considerably cheaper. As in everything - you get what you pay for.
One last thing, if you feel that placement on a range finder sounds problematic - what I love about such a system is the 'visualisation' process that I go through. I like to 'imagine' the final image, and not having direct feed back (via an LCD screen) is a benefit, also being able to imagine the scene in my head and place the filter accordingly, allows me to remain in the 'creative-mode'. Being confronted with real world feed back takes me out of this 'creative-mode' and into 'editor-mode' which is something that I feel kills my creative flow when out shooting scenes. So yes, it's a benefit to me rather than a hindrance.