I’m sure you’ve all seen those fancy HDR photographs of ominous clouds, imposing buildings, and rapturous sunsets. They are all the rage and all over the internet. The basic technique is simple: take several shots of the same scene, each at different exposure values, and use some specialized software to layer all these images together to create a single image that brings out the most dramatic lighting aspects from each of the individual photos.
That’s not what this post is about.
This post is about focus.
I’m paranoid about focus. I use a super steady tripod. Mirror locking. A remote shutter release. I wait 5 or 10 seconds after the mirror has dropped to insure that no lingering vibrations are present. I listen for passing cars and planes passing overhead. I wait for complete quiet and, still, I hold my breath. Only then do I release the shutter for the split second it will take to capture my image with a minimum of interference. Even then, I go through the same process a second time, just in case I missed anything that might bring the slightest bit of vibration into the equation. I don’t know, maybe I somehow made the lens move with an impure thought.
One day I was thinking about HDR photography, and the potential for using similar concepts to create deeply focused images. If an single image could be created from multiple exposures, why not a single image from multiple photos taken with different focusing? After a bit of research I discovered that the technique I was pondering is called “focus stacking,” which is frequently used in macro photography. Moreover, as expected, software packages exist for the sole purpose of stitching together deeply focused images from multiple shots.
That’s nice, but I prefer doing things myself. Besides, I didn’t have an immediate need to focus stack, so I placed it on a back burner where it could get a few cycles of my brain now and then in the event that I’d ever need (or want) to conduct an experiment.
And that’s what this post is about: developing a DIY technique for building a focus stack from Aperture, Apple’s high end photo processing software.
The Background
I’ll be the first to admit that I am a different type of photographer. I don’t take pictures of people or trees, ferris wheels or stunning sunsets. I don’t go on exotic shoots, take vacations, or ask loving couples to “look serious but in love.” No, I don’t do any of that.
I take conceptual photos of bizarre scenes I build myself from records, books, toys and interesting objects inside a 30″ light tent in my studio. This, of course, is quite fun! It’s also quite challenging. You see, I’m a bit of a perfectionist, and I want every object in the frame to be as sharp and in focus as possible. In developing my style I’ve always preferred to maintain deep focus from foreground to back, as my photos are filled with lots of small, relevant details that act as clues in deciphering the story being told. This can be devilishly hard to do when shooting a fairly deep scene from a close, low angle. My solution is usually to focus on an object somewhere near the middle of the scene using a calculated depth-of-field, and shoot a half dozen shots using a different aperture value for each. I then select the shot that brings the most objects into focus, and use that as my master for all image adjustment.
Hey! Why don’t you just choose a smaller aperture like f/18 and increase the exposure? That’s Photography 101 for increasing depth of field!
True! Of course, I’ve never taken a photography class and I just barely know how to use one third of the settings on my camera, so I just go with “what looks good to me.” While a small aperture might deliver an image that is, technically, “in focus” from foreground to back, at no point is the sharpness as sharp as the sharpest objects when taking the same photograph at a much larger aperture. This may not be true for an image you take outside at a distance, but it most definitely is when shooting in my studio, so I’m not a big fan of aperture values above f/14.
Enter, the scene that’s just too deep for one point of focus
Recently, I completed work on a new photo, Engine 316 takes a detour on the glorious path to the Hereafter, a piece that spent several weeks set up in the light tent while I constructed the stage, worked on the composition, and finalized placement of all the figures and objects. A photo of the staging is below, taken from well above the point at which I intended to set up the camera.
Staging for "Engine 316 takes a detour on the glorious path to the Hereafter"
The camera was placed just outside the light tent at a height somewhat below the two Lego “towers” (functioning here as stands for two spot penlights illuminating the kewpie dolls standing inside the log cabin on the right).
The light tent is 30 inches wide at its base, and the scene being captured fills a great deal of that space. The width, however was not the problem. The greater challenge was the depth of the scene which, from the record cover in the back to the “scorpion woman” in the right foreground is approximately 17 to 18 inches. Under most conditions, 14 or 15 inches of depth would be no big deal, but when the camera is to be placed 19 or 20 inches from point of focus (the “scorpion woman” emerging from the records at the center of the shot)… you have a huge, almost insurmountable problem!
Initial attempts to set a single auto-focus point, or multiple evaluative focus points failed to bring enough of the scene into sharp focus, and with good reason. According to depth-of-field calculations, the best I’d be able to expect with a 36 mm focal length from my shooting vantage point was about 5 or 6 inches of depth before the focus began to noticeably break down. Sure, I could have decreased the focal length to increase the depth of field, but this would have altered the photo in two ways. One, the scene would no longer “fill the frame,” as the lens would have effectively been pulled back from the point of focus, thereby limiting my ability to print the scene as large as possible. Two, small changes in focal length alter the perspective of the shot, so when the focal length changes, so too does the position of each figure relative to all the other figures; an effect that is magnified when shooting from very close to your subject.
I saw this photo as a perfect opportunity to experiment with the concepts I was still mulling over for creating focus stacks from within Aperture.
In subsequent installments over the next few days we’ll discuss how the photo was eventually shot, and how I was able to successfully construct a deeply focused image from multiple images exported from Aperture.
[...] 6 separately shot photographs using the “focus stacking” technique I wrote about in a previous post. This time around each photo was shot at a different aperture setting so that the depth of field [...]