Are there any benefits to using graduated filters?
In many situations the results would be the same but there can be benefits of using filters rather than multi-shot combining in post. One is just simple satisfaction of nailing the shot in camera and getting a single exposure for the scene you wanted to capture. Among other things it means when you review the image in the field you can see whether you got what you're after instead of two or more shots that you have to trust will blend well in post for the final result.
On a more practical level if there's any motion in the scene that spans the dark/light boundary a single capture with a graduated ND filter can capture that in a single shot where blending two or more shots can be tough if anything in the scene moves, especially if the moving part is partially in the brighter portion and partially in the darker portion.
Maybe if I use a graduated filter but also use HDR bracketing it would be beneficial.
I don't see many situations where you'd need to use both an ND grad filter and bracket images for HDR blending in post but it's certainly possible and maybe in some crazy high dynamic range scenes that might be helpful.
The bracket and blend approach is really handy when there isn't a clean split between the darker and lighter parts of the image. So for things like architecture where you want an indoor shot that also looks out a window and the dynamic range is many stops beyond what the camera can reasonably capture a bracketing and blending approach works nicely as there isn't a simple horizon line splitting the different exposures. In landscape work that might be something like shooting sunrise or sunset through rock arches or something like that where there isn't a simple horizontal or diagonal line to split the scene by stops of exposure.
FWIW, there are basically three ways I've used over the years to deal with HDR landscape scenes like sunrise reflection shots with both sky and a reflection of sky:
- The simplest but most limited is simply to shoot a modern camera at base ISO (or whatever ISO gives you the highest dynamic range), don't over expose the highlights and simply pull up the shadows and/or make final exposure adjustments in post. If there's only a stop or two of difference in best exposure for bright and dark portions of the scene this can actually work pretty well though it wouldn't have worked well with film or early digital cameras with their much more limited dynamic range.
- Use a graduated ND filter to bring down the scene's dynamic range in the field. BTW, there are hard and soft versions of ND Grads and you may have one or more of each. The difference is how sharp the transition from light to dark is. Some scenes have a very sharp transition from light to dark and others make that transition more gradually so hard and soft versions of ND Grads can help to avoid a very obvious transition line in scenes where the natural transition isn't on a hard boundary. They also come in different strengths like 1 stop, 2 stops and 3 stops. I usually used 2 or 3 stop filters in hard or soft transitions depending on the scene and the lighting.
- Bracket multiple images and combine in post. This is perhaps the most flexible but works best if you capture exactly the same scene in each shot so hopefully no, or very little movement of anything in the scene from shot to shot and with a camera mounted securely so the scene lines up well from shot to shot though you can sometimes hand hold these if you're careful and don't mind doing a bit of image alignment and potentially cropping in post to make sure you're only combining parts that line up well. Shooting these from a tripod or other solid support makes the process much easier.
And sure in some cases you could combine methods though usually one of those will work for most stuff.
