Repeat photography for study of seasonal change
Retake pair, using distant Goat Mountain for photostation alignment
Until 1988 I abstained from cameras, content with pencil sketching and pen-&-ink illustration. But in that year, my parents insisted that a naturalist studying succession should have a camera—and bought me one. Around that time, I also met Minnesota ecologist Don Lawrence, who helped me set up an archive system for my growing 35mm slide collection, and got me started taking photos to document long-term changes to plant communities.
A few years into my film-photography career, I began to think about rephotographing more rapid, cyclical forms of change. How does a leaf or flower unfold? How does beach meadow change through the seasons? Ecologists call study of such life-histories phenology. In the early nineties, mostly near my home at Asx‘ée, twisted tree (Eagle River delta), I set up photo-stations that could easily be reoccupied in spring, summer, fall and winter.
Until winter & spring of 2020, intimidated by the enormous size of my 1988-2001 slide collection, I’ve only taken time to scan the best and most ilustrative, integrating them selectively into journals, reports and slide presentations. The notebook for Seasonal Repeats alone contains 400 slides. But as for many of us who habitually work (and play!) at home, “sheltering in place” is nothing new, except maybe a time of even richer productivity. Jim Mackovjak has purchased a PacificImage slide scanner for his recent book projects, and this spring I have it on loan, slowly working through my old kodachromes in a more systematic manner.
Simply digitizing these slides is only the first step. As described in Repeat photography reports with Kathy Hocker, exact alignment of successive images is a slowly acquired skill demanding patience both in the field and back home on the computer. We sometimes moved our tripod side-to-side, forward and back, for up to an hour before feeling sure that all 4 corners of the frame exactly matched the original photographer’s.
Of course, when you are the original photographer, it’s potentially easier. But only if you had the foresight to drive a stake for tripod relocation, or make a sketch including landmarks for precision replication. Don Lawrence always wrote the millimeter lens setting on his slide mounts, even in days before zoom lenses—when that infinitely variable parameter becomes even more important.
No matter how much care was taken in the field, when viewing the before-and-after, side-by-side, or better yet, ‘toggling’ same-scaled views on your monitor, you’ll discover slight misalignments. We minimized these by dropping the retake on top of the original as a semi-transparency. In Photoshop, it can then be scaled and rotated to more exactly match the underlying original. In this example of the driftlog and Goat Mountain, I was able to precisely line up the distant summits, but that left the rootpad grossly out-of place. Obviously my tripod was off by at least a meter. I then used Photoshop’s ‘warp mode‘ to tug it into place.
Here’s a 3.5-minute slideshow with some background on repeat photography for seasonal (and other short-term) change. Dissolving between slides is a useful technique for helping the eye detect ‘movement’ of a growing plant or eroding river bank.
Cover of a repeat-photo sampler, version-1
But a canned slideshow moves at the presenter’s pace—in this case, probably too fast (unless you’re a teenaged gamer) to fully absorb the messages in those shuffling images. In contrast, pdf format lends itself beautifully to repeat photography, with pairs or longer series presented on successive pages.With your keyboard arrows, or with one click of your mouse roller (change this in Acrobat settings if it’s not the default), you can toggle back and forth, meanwhile holding your finger or the pointer to desired areas of interest, and taking as long as you want, to scrutinize every detail.
Here’s an early draft of such a pdf version of Seasonal re-photography. Because spring’s immediate goal is to get all these slides scanned, RC_RPs_v1 is just a sketchily annotated sampler. More to come! (PS: minor updates to this pdf made in July, 2020)
