Looking Sharp: A focus stacking tutorial
1 Shooting the Scene
This was taken in the deserts of Southern Utah at Snow Canyon State Park near St. George, Utah.
Background: Understanding the Process
One of the questions that I receive quite often from beginner photographers is “How do I produce tack sharp images from front to back in challenging shooting conditions or in cases where the foreground fills up nearly half the frame?” The answer in short is to utilize a process known as focus stacking. The answer is simple but the process can be very labor intensive from a shooting and processing standpoint.
Even when working with a large depth of field there may be occasions where you still have to take more than one image due to low light, wind and or large foreground subjects. Most technique books will tell you that this is easily accomplished by stopping down to a very small aperture such as F22, focusing on a set focal point at about 1/3 of the way into the frame or determining the spot from your hyperfocal distance (the distance between a camera lens and the closest object that is in focus when the lens is focused at infinity), focus at that spot and take your image.
|Here's one of the images that I used during focus stacking. This was shot at 35mm and at f/2.8 due to conditions at the time of shooting. As you can see it was impossible to achieve sharp focus throughout the image.|
In principle this sounds like a very quick and easy fix to a somewhat complex problem that plagues most landscape photographers. In practice, however, it comes with a couple of big issues. Not only can using an aperture this small decrease image quality due to diffraction, it doesn't actually deliver the maximum possible depth of field. That's where stacking comes in. In the digital age we can now improve upon this technique and produce higher quality, tack sharp images from the front to the very back of the frame.
Before diving into this process I should mention that you may not always need to use this technique and this process is really up for interpretation in regard to what you define as a ‘sharp image’. The lens quality and aperture play a huge role in whether or not you wish to go through the work of focus stacking an image. In general, I always use this process now as I want my images to look tack sharp even when printed at very large sizes.
Selecting the Aperture
Choosing the aperture is an important first step to this process. I always try to choose an aperture in the ‘sweet spot’ of the lens. This is a bit of a loaded term; you have to decide whether you are after maximum resolving power or greater overall focus in your image. These differences may be subtle in some cases, but regardless I always try to choose optimal sharpness over depth of field in an individual image, bearing in mind that I'm going to be stacking multiple images. I would rather take a few extra shots to ensure that the RAW files are of the highest quality I can achieve given the conditions.
Generally speaking, the sweet spot of a lens is about 2.5 to 3-stops from the maximum aperture. This does vary from lens to lens however; for example, I normally shoot between f/8 and f/11 when possible on my Canon 16-35mm f/2.8L ii to achieve the sharpest results possible (which I know is a few stops greater). The bottom line is to get to know your lens! You can even run it through an aperture progression and compare the images to find that coveted lens ‘sweet spot’.
Behind the Lens
Focus stacking can be very tricky when you’re out in the field. I use the following steps to ensure that I don’t miss a focus point and to make adjustments on the fly in changing conditions such as light, wind and rain.
- Find your desired composition and make sure that your tripod is in safe position that won’t allow for any movement or shifting while you’re performing the in camera focus stacking.
- Place your camera on your tripod, turn on live view, switch your lens to manual mode, make sure that your camera is set to manual and dial in your composition.
- Once you have the composition dialed in lock your camera down on your tripod and make sure that your ball-head or camera mount is completely locked down so no movement can occur during this process (if some movement does occur you can try to correct this using Auto-Align in Photoshop, but I always try to avoid this to the best of my ability).
- Use either your camera’s in camera timer (set for 2-10 seconds) or use a remote shutter trigger to avoid any camera movement issues.
- Once you are 100% sure that you’re happy with the composition it’s time to adjust your settings; I always fire a few test shots to ensure that I can freeze the foreground subject (flowers etc.) and to see what I can get away with in regard to ISO/Aperture/Shutter-speed while still yielding an acceptable result with respect to proper exposure and the signal to noise ratio.
- This may sound trivial but play with your settings a bit to find the right exposure/sharpness balance; aim to keep the ISO at base and the aperture as close to the ‘sweet spot’ as possible (f/8-f/11 in most cases) this may not be possible depending upon conditions, so make adjustments as you see fit.
- Adjust your CPL or lens filter (ND etc.), if you're using one, to give the foreground more pop etc.
Now comes the fun part: how do you make sure that you have everything in focus and that you don’t miss a focus point? There’s definitely more than one way to go about doing this, but I generally focus on the foreground elements that are closest to the lens; normally near the bottom 1/3 of the frame in live-view.
|I normally zoom in to my area of interest in Live-View and dial in my focus point using manual focus. After taking the image I repeat the process for my next focus point.|
- While in live-view, zoom in to the bottom most portion of your foreground subject and manually adjust the focus until everything is sharp and adjust your settings depending upon conditions (wind etc.)
- To find your next focus point stay in live-view, zoom in to the same area you just photographed and move up in the frame to find your next focus point
- Repeat this process until you reach the background elements in your image and take your final exposure.
- You may want to bracket your last exposure to keep the highlights and shadows from clipping or to catch a sunstar; if you’re shooting on a camera that has a great deal of dynamic range (like a Sony a7r/ii or Nikon D810) then you may be able to do this with one exposure; it’s completely up to you
The toughest thing about focus stacking in the field is dealing with changing conditions such as wind, rain and light. When wind is an issue I always run through at least two or three focus stacking progressions to ensure that I have a sharp frame at each focus point. Even in perfect conditions I still run through a focus point progression at least twice to ensure that I haven't missed a point. There's nothing worse then getting home after a long day of shooting only to find that you completely missed a focus point.
Once you take your camera off of your tripod or move your tripod, it will be a huge pain to get everything lined up again and you may not even be able to in most cases. Double and triple check your exposures to ensure that you’ve got all of your focus points nailed down before moving your camera and packing up your gear.
|The Big Catch by Domenick Creaco|
from grey challenge
|Led Z. 1977 America Tour, Detroit-0003 by vbuhay|
from 70s Nostalgia
|NeoStrike by McWoodley|
from Comet NEOWISE
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