What is the advantage of carrying a tripod and ND-filters when you could use image stacking instead?

Question

From my understanding, if you want to take a long exposure of a landscape shot like the picture below, you have two options:

1. Carry a heavy tripod everywhere you hike and then use a series of expensive ND filters to take a 30 second exposure.

2. Take a succession of quick pictures and then use image stacking software to align them and average them together in post. This has the added benefit of eliminating hot pixels and image noise.

I understand this may have been more difficult in the past due to memory card usage and computational requirements, but in 2019 is there any reason to still carry a heavy tripod and ND-filters to make long exposure photographs like this?

Answer 1

I'd like preface my answer with a note that a tripod is not only useful in conjunction with ND filters — it also improves the results from image stacking as well. By fixing the position of the camera, the tripod eliminates changes in perspective, which can occur through minor motion while hand-held shooting a sequence for image stacking.

Aside from fixing the camera's position, the tripod can also eliminate low-frequency motion blur, when correct tripod technique is employed. This allows for long-duration shutter exposures. Note that the two concepts, fixing the camera position with a tripod, and elimination of low-frequency motion by use of a tripod, are not necessarily entirely the same thing.

"Dumb" (but otherwise still very good) image stacking can't account for changes in perspective, which in the most fine-grained terms is the precise location of the camera's entrance pupil. So hand-holding a camera and taking, say, 50 or 100 images, while slightly moving because of body motion, may result in more images in the stack being thrown out. Worse, those images might not be thrown out, and they get averaged into the result, which contributes slightly to lower sharpness.

Conversely some of the latest smartphones, that have 3D depth mapping capabilities in conjunction with really good computational photography algorithms, can theoretically deal with small shifts in perspective (or if not now, then they will be able to soon, at cheaper and cheaper price points). That will certainly improve hand-held image stacks to simulate/recreate long-shutter ND filter shots. But in my opinion, that's no reason to rely on technology to make up for a simple problem in technique. Instead, why not augment the power computational photography algorithms with good tripod technique. Everything you do to help the camera produce the best results it can create will only improve the achievement of your artistic vision. If the weight and bulk of a tripod is a concern, you can look for new tripod technologies, such as Peak Design's recent compact travel tripod

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Regarding ND filters vs image stacking, I'm a fan of of the slow tripod-and-ND filter route. I like the process of taking my time, setting up the tripod and filters, computing the exposure, selecting my filters, etc. I enjoy the challenge of trying to balance the exposure as correctly as possible in camera.

When it comes to scenes that also have to balance dynamic range in different zones by using graduated ND filters, image stacking may or may not yield the same results. I mean, it can yield the desired results, but you'd have to take a stack of images exposed for the lightest parts of the scene, and then take a stack of image exposed for the darkest parts of the scene, and mix those two stacks in post. It absolutely can be done (and has), but it's not the route I prefer to go, when I can just use graduated ND filters to mix the dynamic range in camera.

Now, there are strong arguments for doing away with graduated ND filters, and just mixing exposures in post. This is really just a type of HDR or exposure fusion. And this can also apply to long-exposure ND filter type shots as well. But again, without physical filters, you're essentially performing 3 post-processing steps: image-stacking the high exposures; image-stacking the low exposures; and HDR/exposure-fusion blending the stacked results together.

Answer 2

Well, with regards to your (1)... You could carry a light tripod (or beanbag or any other way of stabilizing a camera) and use only a single ND filter instead of several stacked filters.

With regard to (2), yes you could do that, but stacking a sequence of discrete single images will give you a result that contains several discrete non- or less-blurred images of moving objects rather than a smooth continuous image of the path of the object. That might not be important in some cases, depending on the subject matter, but then again, it might be a significant difference in the results.

Answer 3

For me the main advantage is... Joy.

I enjoy a lot more taking photos, people places, products, rather than editing the images, especially on automated tasks, like stacking photos. Of course, there are some parts enjoyable, like tweaking the final result. But, overall, I prefer not having a ton of shots to review.

Taking a long exposure image on site gives you the advantage of reviewing it at the spot, make corrections, change framing, etc. There are instant satisfaction and feedback.

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One advantage about the stacking is that you can control more of the process, for example removing people from locations, but overall, I prefer the photography side of photography, rather than the automated staking side of it.

Answer 4

For use cases where image stacking might often be the preferred technique over single long exposures, a tripod or other physical method of stabilizing the camera is still invaluable and almost always the best technique to get the best result. It also significantly reduces the time spent on post-capture work per finished image.

Answer 5

1: I typically carry just a light tripod and a single 10-stop ND filter. I find that this is stable enough.

2: Taking multiple pictures would work but sometimes you can get gaps between pictures (this can be solved by taking lots of pictures which would take longer). I don't like to do it this way since you don't know how the image will turn out until after you get home and process them.

You can take a compromise and take multiple pictures with an ND filter and tripod and average them later which is what I typically do. It's the best of both worlds since you can see the end result immediately and you can average them to decrease noise.