Focus Stacking for Landscape Photography and Understanding the Limitations of Hyper-Focal Distance
In this TWO part tutorial I will discuss depth of field, hyper-focal distance, their limitations and the ins and outs of focus stacking as a way of overcoming them! Enjoy!
The What and Why of Focus Stacking for Landscape Photography
Focus stacking, put simply, is a technique where you capture multiple frames of the same image with a different focus point in each frame and compile them to create an extreme depth of field. This is very commonly used in micro and macro photography to overcome limitations of extreme magnification and depth of field when capturing very small subjects. So, how does focus stacking for landscape photography work and why would we use it for landscape photography you ask?
Well, all lenses have limitations when it comes to depth of field. The relationship between aperture and focal length dictate just how large our depth of field “bubble” is and what is in focus and what is not within the frame. The nature of the optics within the lens and their magnification power limit what we can capture in focus in a single image. Engineers and physicists have been working to solve this limitation for decades.
The closest we have come to remedying this problem is lenses with variable apertures like the lenses we use today. By controlling the aperture in your lens, you can restrict the amount of light being revealed to your cameras sensor. By way of some very sophisticated and incredibly confusing physics, these blades and internal optical components can shift your depth of field. I dont fully understand it myself so I won’t go into detail there. This diagram below will help you understand.
Despite these limitations, there are aperture and focal length combinations where you have the maximum amount of ‘things’ within the frame that are “acceptably sharp” based on how far you focus from the camera. This is known as hyper-focal distance and is a complex calculation based on those variables (see below).
For example, when we focus on something less than 10 inches or so at 14mm at ƒ/16 our depth of field is maybe a few inches deep. If we were to keep the same focal length and aperture but focus on something let’s say 10 feet away, our depth of field is infinite after ~ One foot, 5 inches or so (to understand how I came up with this figure and why I chose ƒ/16 as an example, read below). Imagine a giant invisable bubble that sort of only grows bigger and only away from you. This seems to help some people visualize how depth of field works.
Of course “acceptably sharp” is a subjective term and not everyone shares the same opinion of what might be labelled “acceptable”. If you’re like me, and want every detail from the nearest blade of grass to the wispiest cloud miles away, as sharp as possible, then hyper-focal distance will simply be inadequate; which is a major part of the reason for this article. Read on for more…
There is always an area between this focus distance and your camera though, where things are not in focus, and herein lies one of the limitation we’ve been speaking of. This area is where, at our hyper-focal distance, or the focus distance that is allowing the maximum amount of depth of field and therefor things in focus, are not in focus. This area is so close to the lens that you simply can not get what is in that area to the distant background in focus and be acceptably sharp.
Referencing the scenario we spoke of earlier and our hyper-focal distance of 1’5″, approximately the first 8-10 inches between your camera and the hyper-focal distance point will be out of focus. If we were to focus any closer then the background would be considered subjectively as “un-acceptably sharp”.
I know, this is confusing, but to make it easier, Apps like PhotoPills have hyper-focal distance charts built right in! Simply find the intersection of the aperture and focal length to find the hyper-focal distance (read here for a tutorial on using PhotoPills Hyper-focal Chart Pill)
By now you have to be wondering “why not stop down smaller?” makes sense right? Well not to me. Read on.
Up until the invention of focus stacking softwares and the inception of the concept, the only way to get as much in focus as possible in one frame was to stop down to the smallest aperture your lens would allow. In most cases this was ƒ/22 but in some cases lenses could stop down smaller. This however is still limiting and doesn’t completely solve the problem, as well as it creates a new and maybe worse, problem. Diffraction.
Diffraction is an optical anomaly that degrades details within a photograph much like being slightly out of focus, but different. Imagine astigmatism for your camera. It is defined as “the bending of light waves around the corners of an obstacle or through an aperture into the region of geometrical shadows of the obstacle/aperture”, according to Wikipedia. Basically it just makes your photo less sharp. Therefor you reach a point where you are stopping down (or making the opening in your lens) SO small that you begin to trade a larger depth of field for less sharp objects.
Diffraction is the reason I chose ƒ/16 as my example above. It is my personal threshold when using my copy of the Nikon 14-24 ƒ/2.8 lens above ƒ/18, I experience more diffraction than I am comfortable with in my imagery. This can vary with the age and quality of your lens as well as from one manufacturer to another based on their technology but is very common in most lenses.
If you’re still reading then you probably shoot a lot of near/far, close-up wide-angle images and have probably noticed the not so great affects of these limitations. For those of you that want to take full advantage of wide-angle lenses this is something to consider for when you do.
The decision of whether or not you employ this technique and go through all of this work should come down to firstly, your vision, and secondly, your application. If you want to utilize compositions like these in your imagery and in order to capture those critical first few inches where hyper-focal distance fails, as sharply as possible; as well as the distant background elements for a truly huge depth of field, without diffraction, then it is required. If your photo will only ever be viewed on a phone or in small resolution then it may not be worth the work. Using hyper-focal distance and not being quite as close to your foreground probably works for you, but if you desire the sharpest and most detailed photos with the most extreme depth of field and close up foregrounds possible or enjoy printing large this information is for you!
Most wide or ultra-wide angle lenses have a minimum focusing distance that is smaller than the hyper-focal distance point. Meaning we can focus much closer than the hyper-focal distance point. In the case of this example, I am using the Nikon 14-24 ƒ/2.8 Lens with a minimum focusing distance of ~0.9ft (10.8 inches). That is as close as we can possibly focus using this lens.
For example, Imagine we are at an alpine lake, we’ve hiked for miles. We arrive to incredible mountains, looming high over our heads, storm clouds swirling around and the sun piercing through the haze like a laser. Wildflowers are growing like a carpet and would make a beautiful and interesting foreground. You set your tripod up as low as it can go, you zoom all the way out to 14mm and ƒ/16, focus on the flowers and WOW! the flowers, they’re huge! and SO interesting! But I can’t seem to get them, and the amazing mountains in focus… What do I do??
You have no choice but to focus stack.
The How of Focus Stacking for Landscape Photography
Focus stacking, put simply is where you take several photos, moving your focus point back each time until you have a frame for every inch of the scene, with some overlap.
If we have an area of about 8-10 inches according to the settings mentioned earlier, that is not in focus according to the hyper-focal calculation; and our lens has a minimum focusing distance of ~8-11 inches. Then we have a few inches where we can use the lenses distortion and exaggeration of close-up elements to our advantage, which is such a powerful technique for creating that immersive perspective. Though, because focusing that close, our depth of field is so shallow we will have take a photo for different parts of the scene until we have captured the entire scene in focus. Starting with the closest possible thing we want to focus on and ending when we either reach the infinite focus point of our lens or all of the elements we want are in focus. Then we’ll compile the images so that it is one, unified image, ready for creative wizardry.
For example, the image below, titled “Absolution” was captured at the settings above in 2018 in Glacier National Park. It required 5 frames for focus and 1 darker frame for highlight recovery.
Below is a pictorial illustrating where my focus points fell within the image to capture all of the available detail. Notice how the spacing between each focus point grows? This is because our depth of field is growing each time we focus further away. It’s important to remember to have some overlap between each frame. Zoom in when reviewing the image in your camera to find where the focus is ‘falling off’ and focus somewhere just before that point. After some practice this will become quick and thoughtless!
- Step 1: Determine your settings. Smaller apertures will mean you will need less photos to ensure sharpness throughout. A bigger aperture and shallower depth of field will mean you will need more photos. The deciding factor for me when using available light is to determine if a fast shutter speed is important, for say, flowers. If so, I would opt for a higher ISO and smaller aperture to maintain a fast enough shutter. If shutter speed was irrelevant, I would simply use a small aperture like ƒ/16 and allow my camera to take longer exposures to keep ISO lower. Oftentimes I employ this method when shooting wildflowers and commonly use settings like ƒ/11-ƒ/16 and ISO 500-1500 and shutter speeds anywhere from 30 seconds to 1/80th second. Don’t be afraid to push ISO a little to gain better depth of field if the occasion arrises. Wind of even 1-2mph can make shooting flowers or foliage very tricky when it comes to blending!
- Step 2: Focus as close as you need to, to get your closest included object in focus. After capturing the frame review it and zoom in to inspect where the sharpness falls off, or where things become soft or out of focus.
- Step 3: Re-focus just before where focus falls off and take another frame.
- Step 4: Repeat step 3 until you have captured the entire scene. You’ll notice that if your lens has a focus distance scale on it, these distances will correlate and end at infinity if you have very distant focus points. If required, bracket your last frame for dynamic range.
- Step 5: Blend it all together.
Stay tuned for Part 2 of this article to find out how we blend all of these pictures together using Adobe Lightroom and Photoshop!
Here are a few more examples of extreme focus stacks of very near far compositions. Enjoy and thank you for reading!
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