Graduated ND filters are a pain in the arse, bulky, expensive and are completely unnecessary for digital photography. With multi-image, post-processing techniques you can get better results than were ever possible with the filters.

With film the most common use of Grad NDs was to balance an overly bright sky with the rest of the scene in a landscape shot. Filter strengths of one or two stops was typical... more rarely three stops. I can't recall ever using stronger than that. There are also soft, hard and medium transitions, largely depending upon the type of lens being used. A wide angle lens usually required a soft or medium gradation, while a telephoto might need a hard transition. Of course, it also depended upon the scene. Sometimes a soft transition was better... sometimes a more abrupt one was needed. I only ever carried soft and medium transition filters. (There also are reverse Grad NDs, Center Spot ND and some other specialized types. I never really had any need for those, except for a Center Spot that was matched to a particular wide angle lens that had a lot of optical vignetting... the filter corrected that.)

While there are round, screw-in Grad ND filters, those were particularly limiting. They position the transition from clear to ND right across the middle of the image, pretty much forcing you to place the horizon line in exactly the same place in every shot you took!

Better were the rectangular, oversize filters.... which are fitted to a holder that's in turn attached to the lens with an adapter (that allows them to be used with various lenses that have different diameter filter threads). The rectangular filters can be rotated as needed and slid up or down to best match the horizon line. A Sigma 10-20mm f/3.5 lens has an 82mm filter thread, so probably at least 100mm x 150mm ND Grads would be needed to avoid problems with vignetting.

The problem is, even with the rectangular ones the transition zone from clear to ND is always a straight line across the filter... but horizons rarely are perfectly straight. Or, perhaps it's that the more interesting horizons we might want to photograph aren't typically straight. As a result of this mis-match either part of the scene that shouldn't be held back by the ND section of the filter ends up covered by it, or part of the brighter sky you wanted to hold back by the filter isn't covered.

In addition, quality Grad ND filters ain't cheap. Sure, there are cheap ones made of optical plastic. But those scratch easily, are difficult to clean and usually aren't multi-coated. Better optical glass filters that are multi-coated tend to cost around $150 or more each. There are even some more expensive that combine features like warming or color enhancements with ND (also unnecessary with digital, since individual color channels can be adjusted independently and white balance is so easily tweaked... in fact, if using auto WB, it will usually cancel out a filter's warming effect).

My recommendation for a landscape photographer instead is to simply take two shots: one exposed for the sky, the other exposed for the rest of the scene. Later in post-processing you can combine the "correct" portions from each into a single image that's better than was ever possible with the actual filters. There are also Grad NDs built into most image editing software that can be quickly and easily applied directly to a single image, though this may have the same "problems" as the actual filters unless some additional tweaking is done. Yet another method is to double process a single image... adjusting the exposure for the sky in one version and adjusting it for the rest of the scene in the second version, then combining the correct parts from each in the same way as is done with two actual exposures, described above. These post-processing "tweaks" are always best done with RAW files, which if necessary allow for greater range of adjustment than JPEGs. Also, RAW files are worked in 16-bit mode that's more tolerant of adjustment than the 8-bit of JPEGs.

Below is an example where I used the single image, double processed to partially recover a blown out background in an image. This was a moving subject, so there was little opportunity to take multiple images. Obviously, this would have been impossible to do with a filter. While it's not a scenic shot, the exact same techniques can be used with those, too (in fact, with landscape shots it's usually much easier than this image).



Customer liked this pose and wanted a print made from it, but as you can see when the exposure is correct for the indoor, shaded subject, the outdoor, sunlit background is strongly overexposed.



So I created the second version of the image above and adjusted the exposure to recover some of the background detail. I also adjusted the color balance for the difference between the cool indoor shade and the warmer outdoor sunshine.

Then I used layers & masks in Photoshop to combine those two version of the image, with this being the result:



The above final image may appear a little saturated on some monitors. This was deliberate because of the printing process that was going to be used. Also, if you look closely you can see I ended up not using all the "recovered" background version. When I combined the two versions I felt the background was starting to overpower the subject. It was a very simple matter of making that background layer slightly transparent to reduce its strength.

Exactly the same process can be used with landscapes and many other situations. In fact, it's easier because it's usually just the sky that needs tweaking (though if there's a reflection in water, that can require it's own separate adjustments). In the above example I adjusted both exposure and color balance. In other images I've used similar process to selectively sharpen or blur down parts of images.

There are some other ways to do this with a digital image.... All at least as good as using Grad ND filters and a few that give results better than was possible with the filters.

Another thing, the oversize, rectangular filters are difficult to shade effectively with a lens hood. There were some modular and "accordion" style hoods made, but those were only partially successful. Some people just use their hat or carry a piece of cardboard or something to shade the filters.

I still have a several of my Grad NDs from when I was shooting film 20 years ago. I keep them along with some of my film cameras, just in case I want to shoot some. But since learning the post-processing technique described above and since I almost exclusively shoot digital now, those filters are gathering dust in a closet.