Stacking the Deck

“You cannot depend on your eyes when your imagination is out of focus.”     Mark Twain

Canola field with wheel line irrigator

A canola field with wheel line irrigator.

In June and July rapeseed* (canola) blossoms blanket the fields here in a brilliant yellow. Some of those fields are massive, seeming to extend hundreds of acres. Some are pool-table flat, others follow the contours of the hills. Whatever their size and blueprint, when the morning sun lights the blossoms the color overpowers most everything else in view. But that brilliant color is ephemeral, lasting only a few days before the blossoms fade and the fields return to a much less interesting pale green. With time-limited opportunities to make pictures of the fields there's some benefit to planning ahead, previsualizing the photos one might make, and scouting to find appropriate places to stand to do that.

I've photographed canola fields, starting in 2012 when a friend called to insist that I come to see a field she passed every day on her way to and from whatever errands she had in town. Of course I had a look, and found a rusting wheel line irrigator not quite obscured by the tall plants. I went back several times waiting for peak color, and on the best day climbed on top of my old RAV4 to get a little extra height needed to include the wheel line as it receded into the distance. Limited depth of field (DOF), even at small lens apertures, left the blooms closest to me blurred as I focused to make the full length of the wheel line sharp. The photo has been successful (if “success” is measured in sales), and I like it a lot. It captures exactly the picture I had in mind. If I had it to do over I wouldn't change much, but I'd like to see even the nearest plants in focus.

Canola field and Mission Mountains

A canola field below western Montana's Mission Range.

My next opportunity came a year later, when the bloom of a large field lit the valley floor with the Mission Mountains as a backdrop. Bordered by a busy divided highway high above, it's difficult to capture a wide view of the field; the ideal location for the tripod would be in the middle of that highway. While the photo might be very nice, it's probably not worth dying for, although my alternate shooting location may not have been much safer. Across the highway the terrain rises steeply above a bike path from which views of the field are obscured by trees. The best place to stand for that photo is high up on that incline, so naturally that's where I had to be. It's not quite impossible to stand on the hillside, which is nearly vertical. To make up for that it's planted with native grasses, making for a slippery surface. I didn't have much trouble climbing ladder-like straight up the slope; the challenge was turning around to face the field and set up my tripod without falling face-first all the way to the bottom. I ended up sitting with my back against the slope and using the collapsed (short) tripod between my knees as a monopod. Fast moving clouds made interesting light patterns in the field and on the background mountain, so I waited for a nice pattern to appear. Once I'd got my photo I had to slip-slide my way back down, mostly flat on my back, feet-first. I probably looked like a candidate for a Darwin Award. Wouldn't have been the first time. Or the last. But I got a pretty neat picture, with a band of sunlight on the mountainside trees beyond the canola field. I used a long lens for that photo, but the great distance from my shooting location to the field negated the limited DOF; the entire image is quite sharp.

The Fields of 2020

Rapeseed apparently takes a toll on the fields, as I never see the same field planted in consecutive years. It seems every other, or every third year produces better yields. At any rate, the valley field described above once again blazed with canola blossoms in July of 2020, but so did other fields where I'd never before seen it planted. I decided to photograph in those other fields, and this time with a goal, in addition to my usual determination to capture images in great light, of getting maximum DOF, having the fields in focus from the toes of my boots to the horizon. There are several ways to accomplish that: use a tilt-shift lens; set up my shot with camera position and choice of lens focal length, and then determine the hyperfocal distance before giving up because I want too wide a range in focus; or use software to combine multiple images made with different focus points.

I promise I won't try to explain hyperlocal distance, circle of confusion, or diffraction at smaller lens apertures. You're welcome. But it's all interesting stuff, good to know.

I don't have a tilt-shift lens, so that option's off the table. Given that I want sharp focus from inches in front of the camera to the horizon, and that I'll likely be using a focal length in the short-telephoto range, and that my own testing of the lens I expected to use indicates diffraction becomes visible at about F/13, there is no hyperlocal point that'll do the job. Scratch option #2. That leaves the software option, so I did my best to make the multiple image captures that requires.

Focus Groups

This shouldn't be hard. The fields are easy to reach, the weather's great, and I can stand on level ground or, in some cases, on paved roads. I know how to do this stuff, but each new scene or location presents its unique challenges, and a little luck never hurts. I made a scouting run to my first location, wandered around looking at things a little too late in the day for good light, let the ideas percolate overnight, and came back the next morning. It's a quiet area, not much traffic, and I enjoyed working in solitude. It quickly became clear I'd not get the DOF I wanted without using focus-stacking software, so I made exposures for that. I focused on the closest blossoms, and then manually focused farther and farther out to the horizon, making a dozen or so captures for each picture I hoped to assemble. The area had several large fields; I walked around to get a number of different views. Unfortunately the wind came up as I worked. With the canola being four feet (1.2 m) tall it took only a whisper of breeze to move the long stems. I knew this would challenge the software later, but one can't do anything about the wind. A couple of hours work netted lots of files to process later.

At home I transferred the day's files to the computer, chose the best sequences of images, and set Photoshop to the task of stacking those. It finds the sharpest areas of each image, masks out (hides) the soft areas, and produces a blended, sharp image. Sometimes. I expected the wind-driven movement of the canola would reduce the chance of getting a good result, and I got exactly what I expected. None of the stacks worked well enough to keep. While interesting and perhaps educational, the more complex areas of the pictures, such as where the tops of canola stems reached into distant background trees, were just smears of color with no definition either in the blossoms or the trees. I tried manually editing the masks Photoshop created but I had no more success than the software did on its own.

1 / 4
Rapeseed field and gloomy sky.
2 / 4
Rapeseed field and mountains.
3 / 4
Rapeseed field and local hills. This is a single-exposure made with a wider lens.
4 / 4
Rapeseed field below the Mission Mountains.

There are surely better tools than Photoshop for this. Photoshop does many things well, but some things less well, and some downright poorly. That's why there's a healthy market for plug-ins and other specialized software. For focus stacking, Heliconsoft's Helicon Focus (HF) is a major player. I downloaded and installed HF, which can be freely used for 30 days before payment is required. I watched a few tutorial videos, and then gave the program a chance to salvage my image. The result: as close to identical to Photoshop's poor result as I could determine. HF provides some control over the process, some options that can be set. After a quick review of the tutorials I tried again, always with similar results. Clearly HF can't perform miracles; subject movement between frames is tough to overcome. If you look through HF's Web site and the example photos you'll see most are macros, extreme closeups of insects, plants, and other subjects, the kinds of pictures where DOF is minuscule and use of image stacking is standard procedure. The examples are lovely, shot (I'd guess) in ideal conditions, giving the software exactly what it needs to produce a great result. HF can't handle what I threw at it, but it's clearly the right tool when given carefully-made work captured in ideal conditions.

To cut to the chase, I went back to the same area half a dozen mornings, until the fields started to fade to green. Wind continued to confound me, but I did have a couple of calm mornings and got exposures Photoshop could stitch perfectly well. A few of those are shown above, along with a single-frame picture that required no focus stacking.

A few days later while out for a drive Pat and I found another large canola field, this one perhaps planted just a bit later than those I'd photographed. Still at peak color, I returned the next two mornings, and once again got some nice captures for focus stacks easily handled by Photoshop.

Focus stacking is a tool I'll use when needed to overcome limitations in my equipment. When it works, it seems to work well. It's not something I want to use often, given my preference for getting things right in-camera, but it's good to have an understanding of the stacking process, to know when it'll work and when it won't.

*Canola oil is made from rapeseed. Wikipedia is happy to tell you all about it.

July, 2020

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