Utility truck
Gear Theory

Some Rolling-Shutter Fun… From a Moving Bus – By Dave Powell

September 24, 2022

The proverb “Necessity is the mother of invention” is credited to philosophers going back to Plato. But a modern paraphrase claims that boredom is another mother of invention. It certainly was for me in 2018, when my wife and I took a bus tour of Newfoundland.

To be Clear

Actually, this Canadian island is anything but boring! It is spectacularly gorgeous, endlessly fascinating, and enjoys perhaps the most welcoming people we’ve ever met. Also, St. John’s (its lively sea-side capital) is totally “happening”… especially on a warm Friday evening!

But, to tour Newfoundland by car or bus, one spends a lot of time on the province’s 900-ish miles of Trans-Canada Highway. It’s mostly a narrow two-lane road through endless stands of beautiful forest… with occasional rocky outcroppings and exits to coastal towns with names like Blow me Down, Come by Chance, Cow Head, George’s Point, Knights Cove, Muddy Hole, Tickle (Cove or Harbor), Tilting, Virgin Cove and Woody Point!

It was my first major outing with a new Panasonic Lumix ZS100 compact point-and-shoot. It boasts a 1-inch, 20-megapixel sensor behind a 10x stabilized Leica zoom. But I quickly grew bored with all the gorgeous green that passed outside our bus on long Trans-Can stretches, and decided to muck around with something called the “Rolling-Shutter Effect.” For many photographers, it’s a nuisance. But I chose to take the photographic road less traveled and use it to shoot some interesting images from inside our bus.

“Rolling Shutter” vs “Shutter Drag”

“Rolling Shutter” isn’t the same thing as what’s currently called “Shutter Drag.” The latter involves taking long existing-light exposures of moving subjects, followed by a pop of flash to freeze them into sharp focus. (Think of all the shots you’ve seen of dancers spinning and moving within swirling clouds of their own arms, legs and costumes.) The effect can be created in many ways, doesn’t actually involve “dragging” shutters, and might perhaps be achieved fairly easily using a modern camera’s Night Portrait mode.

The Rolling-Shutter Effect, however, was first seen in film cameras whose focal-plane shutters didn’t expose entire negatives all at once– but instead, through a narrow slit that flashed across the film. For example, you may have seen an old photo like this– of a race car slanted as if by speed, on tires that are oval rather than round:

Old French photo of a race car

Photo by the early-20th-century French painter and photographer Jacques Henri Lartigue.

As the car passed Lartigue’s camera, its focal-plane shutter captured thin horizontal slices of the vehicle at progressive locations along the road. The car would appear to lean forward or backward depending on whether the shutter slit moved down or up across the film. And people in Lartigue’s photo lean the opposite direction because he also panned his camera to track the car. [The shutter of Lartigue’s camera appears to have moved from the observers’ feet to their heads as he panned– or (since camera lenses invert the outside world) the shutter slit seems to have exposed the negative from the top to the bottom of the camera.]

The same thing occurs in many film rangefinders, SLRs, and digital cameras. (Most notably, it’s why rotating propellers look bent and broken in digital movies.) CMOS models like my ZS100 may expose their entire sensor to light, but they load its pixel data into memory line-by-line for processing. This can produce the Rolling-Shutter Effect. (CCD sensors, however, are called “global sensors” because they read, process and store all image data at one time… and don’t exhibit the effect.)

Many websites offer advice about avoiding, minimizing or correcting Rolling Shutter. But on the Trans-Can in Newfoundland, while rolling through endless forests, I decided to play with it.

Starting Small

First, an apparently hand-retouched exit-ramp sign:

Road-side exit sign

Good lean!

And a bigger sign:

Larger road-side sign

Then a typical Trans-Can scenic (where the trees weren’t really leaning):

Scene of trees and rocky outcroppings

And a “passing” shack:

Shack slightly leaning

Going for More Slant

But due to perspective, light from things in the middle-to-far distance didn’t move across the ZS100 sensor fast enough to really slant. So I went after closer game: vehicles whizzing by in the lane just outside my window:

Car outside bus window

Cool slant… But timing’s off.

Big truck right outside bus window

YIKES… Too close! And… um… who the heck’s driving that thing?

Man on motorcycle

An Easy Rider, with better timing. (Must remember to shoot when the subject just reaches our bus-driver’s window.)

Utility truck

Pretty good! (The truck’s front slants more than the back because, at this angle, the light from the front is moving faster across the sensor than is light from the back.)

A big truck towing a tiny house with its stairs

OMG… A tiny house (with stairs)– and a driver this time!

I grabbed these shots over the entire trip. It took many trials to optimize framing and image quality. And the files’ EXIF data indicates that they all were shot at shutter speeds from 1/16,000 to 1/5,000 sec, ISOs from 3200 to 6400, and with the lens always open to f/2.8. (I found that smaller apertures made the photos terribly dark and noisy.)

In future trips, I may try to capture different subjects– like trestle bridges– just outside my window. And the next time you’re in a bus over long stretches, give Rolling Shutter a try!

Danger…Danger…Will Robinson!

Though off-topic, I must share the following photo. A whole patch of this dangerously toxic plant was growing behind one of our motels… where anyone (including children) could touch it:

Giant Hogweed plant

Despite appearances, it isn’t Queen Anne’s Lace. Called “Giant Hogweed,” it has meaty, jagged leaves; hairy, hollow stems (sometimes covered with purple-red stains); beefy flower clusters (up to 2 feet across); and heights of up to 15 feet. In Newfoundland, we saw it along roads, in parks, beside public walkways, and around hotels, restaurants and parking lots. It’s also invasive, drought resistant, and spreading in Europe, Canada and the U.S.

Do not touch or burn it (unless you know how to do so safely). And keep children and pets far away! According to the North Carolina Department of Agriculture, its sap causes a severe Photodermatitis skin reaction– with large, painful blisters and eruptions (much worse than poison ivy) within two days of contact. When exposed to sunlight, the blisters may leave permanent scars, and the plant’s sap can cause blindness if it touches the eyes.

Our Canadian tour guide didn’t know any of this… as we strolled by entire beds of the dangerous stuff. So we told them about a New England florist who had cut and gathered an armload of it for his arrangements, walked in the sun back to his shop, and ended up in the hospital with third-degree burns and permanent purple scarring of his hands, face, arms and chest.

If you happen to touch Giant Hogweed:

  • Cover the contact area as much as possible,
  • Return home immediately,
  • Thoroughly wash the affected area with cold water and soap,
  • Call your doctor, and
  • Keep sunlight away from your skin (and hands away from your face) for two days.

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9 Comments

  • Reply
    Roger
    September 24, 2022 at 3:18 pm

    An entertaining, and well crafted post. A pleasurable read to wake up to this morning with that 1st coffee.
    Also…
    Thank you for the warnings & education on Giant Hogweed.
    Why would the gods send us humans such dangerous plants?

    • Reply
      Dave Powell
      September 24, 2022 at 6:40 pm

      Hello Roger. How wonderful that it was a good morning read for you! You bring up a great point about dangerous plants. I hadn’t wanted to mention this in the article itself, but people who know how to do it safely actually EAT the stuff! So that would put Giant Hogweed in the same culinary stable as mushrooms, Blowfish, and other “delicacies” that those not in the know shouldn’t mess with!

  • Reply
    Gary
    September 26, 2022 at 8:01 am

    I may be dense, but I don’t think the article explains (for me at least) how to achieve this effect. With such high shutter speeds I would have expected the photos would be undistorted.

    • Reply
      Dave Powell
      September 26, 2022 at 4:23 pm

      Gary, you’re not being dense at all… it’s a superb question! I first went back to the images’ EXIF files to confirm those blistering shutter speeds. And they did indeed range down to 1/16,000 sec. And I touched on the answer in the article, but with a misleading level of generality. Here’s a more detailed explanation!

      Like many of today’s digital cameras, the ZS100 has both mechanical and electronic shutters. The ZS100’s mechanical shutter handles “slower” speeds of 1/2,000 to 60 sec, while the electronic shutter seemingly blazes along at 1/16,000 to 1 sec. I used the faster electronic shutter because I wanted the victims of my experiment to show more Rolling-Shutter than motion-blur effects.

      In digital cameras with two shutters, the mechanical shutter moves two physical curtains in a way that exposes the entire sensor evenly (without a “moving-slit” effect). Then– only after both curtains close– is sensor data processed row-by-row. And since the image was collected without a moving-slit effect, the row-by-row processing of a fixed graphic file produces no Rolling-Shutter. But old-fashioned motion blur can be more evident.

      My article, however, was less precise about how electronic shutters work! They freeze moving subjects at faster effective shutter speeds because they both capture and process incoming sensor data line-by-line in real time. No moving parts are involved. Light hitting each row of sensor sites is collected and processed before moving on to the light hitting the next row of sensor sites.

      The faster “virtual” shutter speeds come from the shorter time over which each row’s light is collected before it is processed. But the overall time to collect and process the entire view row-by-row can produce Rolling-Shutter– even at “virtual” speeds as fast as 1/16,000 sec. Each row may be collected at such speeds… but the entire image is progressively captured and assembled at longer effective speeds.

      Quite paradoxical actually… and I hope this helps!

  • Reply
    Sroyon
    September 26, 2022 at 8:18 am

    Unusual and interesting article, thanks for contributing! I want to give this a go, maybe with film cameras for added challenge and uncertainty 😀

  • Reply
    Dave Powell
    September 26, 2022 at 7:42 pm

    Thanks so much Sroyon… and you’re welcome! As you might imagine from my reply to Gary’s comment, film might possibly reduce uncertainty a little. (Things are a bit odd in the digital realm.)

    But I also just realized another digital benefit: the ability to choose whether to capture Rolling-Shutter or motion-blur effects… and possibly even both. (Must see if a longer electronic-shutter speed might capture both motion-blur AND Rolling-Shutter… for a real Speedy-Gonzales look!)

    • Reply
      Sroyon
      September 27, 2022 at 10:08 am

      Yes, my understanding is that if the subject is moving fast enough, and provided you use a fast enough shutter speed, you can get rolling shutter effects even with a mechanical shutter.

  • Reply
    Dave Powell
    September 27, 2022 at 2:08 pm

    Worth a try! If you succeed in doing that with film, can you post an image in this comment stream? (My guess is that it’s not possible.)

    • Reply
      Sroyon
      September 29, 2022 at 9:04 am

      Hmm, do you mean not possible with film? But Jacques Henri Lartigue’s racecar photo, for example, was analogue (4×5″ glass plate). This page has a nice explanation.
      I believe most (perhaps all?) film cameras with focal-plane shutters, at fast shutter speeds, expose through a slit; they don’t expose the whole film area at once. So the potential for rolling shutter effect is there. But of course Lartigue’s camera was large-format, so the shutter travel time was longer, and the rolling shutter effect was easier to reproduce. On 35mm or 120, one would probably need to pick a more fast-moving object like a propeller. Anyway if I end up trying it, I’ll post here, successful or not. Thanks for the motivation!

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