So it's not just a simple case of choosing soft grads over hard ones, because you think they will be less noticeable in the final image. You also have to take into account the focal lengths you're using.
In my own case, I use Medium Format cameras, and I mostly use hard-grads because they give me the right amount of graduation across the frame for the focal lengths I mostly use (50 and 80). When I use the hard-grads with the 50mm, the placement isn't so critical as there's a degree of diffusion there already, but the filter still bites into the image enough to make hard-grads a viable choice. When I use soft-grads though, they tend to be too diffused for the focal lengths I use.
Which of the new range will I be tempted to get?
Since I'm a medium format shooter, I'm tempted to replace most of my soft-grads with the new medium grads. The medium-grads will give me what I am looking for (but not getting) from my soft-grads.
I will remain using the standard hard-grads, as they are perfect for my wide and standard lenses, but I am interested in buying some very-hard-grads for use with my telephoto lenses. As explained, when you get up to such high focal-lengths, hard-grads become less and less effective.
Using different types of graduation is a key component to good exposures. I've found for many years that I could do with some graduation filters that are somewhere between the old hard-grad and soft-grad sets, and there is also cause to have very-hard grads for use when using higher focal lengths. So for me, I will be buying some of the medium-grads and very-hard grads to compliment my ever-growing set of ND filters.
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January 2020
As of January 2020, I’ve had time to use the medium grads now for just under four years. I find them indispensable as part of my set of grad filters. I use medium and hard grads just as much in the field and both are used for different reasons that I can summarise as follows:
On longer focal length lenses, hard grads are always required. Zooming in just diffuses any graduation of any kind so they act more like a soft grad when you get up to the 100m focal lengths and beyond.
Hard grads are useful from 50mm to around 150mm. Go wider (below 50mm) and hard grads become too hard.
Medium grads are useful with very very small focal lengths (below 50mm). As you zoom out, the graduation becomes more defined. So medium grads give sufficient feathering.
In summary, medium grads at the right focal lengths do what most of us assume soft grads will do. They are really useful in empty areas of water and sky where we need some bite into the photo without being overly obvious. Using hard grads in empty areas of the photo can be too obvious.
I haven’t tried the very hard edged grads - I feel these would only be of use on longer focal lengths (100m and above). As my article stated above - as you zoom in, the graduation becomes more and more diffused. Hard becomes medium, and medium becomes soft. Soft becomes ineffective.
I have rarely found much use for soft grads. They are simply too soft once placed up close to the lens and the graduation becomes so diffused as to make little to no difference to the photo. Indeed, I find myself often placing soft grads so low in the frame in an attempt to make them bite into the photo that they end up just darkening the whole scene as if they were a full ND.
Hard and medium grads are the way to go. I use both and have all strengths from 1 to 3 stops.