Preventing Time-Lapse Flicker Caused By Mechanical Inconsistencies
A little while back I read a great ebook called Time-lapse Photography: A Complete Introduction to Shooting, Processing and Rendering Time-lapse Movies with a DSLR Camera by Ryan Chylinski (long name, I know....). One of the chapters dealt with the issue of mechanical induced flicker which I thought was a great nugget for any one doing timelapses. I asked Ryan if I could share the info with our readers and he gladly agreed. If you like what you read, consider buying the full book.
You’ve driven across the state. You’ve hiked the distance. You’ve shot in full manual mode, kept a wide aperture and even remembered a slow shutter speed to create some nice motion blur. You get home, render, and hit play.
There it is: Darker frames, lighter frames, darker frames again...
Time-lapse flicker is a nasty thing. The good news is that fully understanding it’s sources and how to prevent, minimize, and correct it is not really nasty at all. This quick chapter provides everything you need.
How to Prevent Time-lapse Flicker
From Chapter 3 we know that large unintended exposure jumps are the enemy, but a perfectly constant exposure across all images or perfectly gradual exposure adjustments aren’t exactly as easy to achieve as they might seem.
Preventing flicker usually requires an attack on three fronts:
- The right in-camera settings to eliminate automatic frame to frame luminance changes
- Understanding the camera’s mechanical exposure inconsistencies
- Considering deflickering in post-production
Understanding Mechanical Inconsistencies
The second most common cause of flicker doesn’t have anything to do with your camera’s exposure decisions at all but rather lies in the mechanical components in the camera itself.
Errors, inconsistencies, deviations, call it what you’d like but even though automatic DSLR camera apertures and shutter curtains are highly engineered devices, they cannot produce the exact (and I mean perfectly exact) mechanical formations each and every time a photograph is taken, even if the settings between shots remain exactly the same. To minimize time-lapse flicker here’s what we need to concern ourselves with:
Minimizing Shutter Flicker
DSLR cameras have mechanical curtain shutters that control the amount of time the camera’s image sensor is exposed to light. Think of two opaque curtains, somewhat accordion like, that can expand and collapse in front of the sensor.
During slow shutter speeds the first curtain is released from an expanded position and folds downward revealing the image sensor. After the required exposure time the second curtain, which was in a folded state, is now released and expands to block the sensor. The curtains then reset for the next shot and the process can be repeated.
EMBED CODE (slow motion shutter and aperture)
As you can imagine for very fast shutter speeds much more precision is required.
At faster shutter speeds both curtains need to be active at the same time. In order to get very quick exposures the second curtain is triggered before the first is fully opened. The result is a horizontal slit or gap that travels vertically across the image sensor. The faster the shutter speed the narrower the slit and the shorter the exposure.
Very small curtain timing inconsistencies from one frame to the next produce slightly brighter or slighter darker frames when we watch them together in quick succession.
The good news is that shutter flicker is usually much less pronounced and even easier to fully eliminate. By simply keeping our exposures below 1/60th of a second we should be able to effectively minimize this form of flicker.
Minimizing Aperture Flicker
The same frame-to-frame inconsistencies that sometimes affect a high speed camera shutter also affect the lens aperture and it’s the last form of flicker we need to worry about.
The camera’s aperture functions much like the iris of your eye - it controls the diameter of the lens opening and subsequently how much light passes through to the image sensor. Now normally when shooting in full manual mode you would think that the aperture setting or f-stop would remain perfectly constant between shots. A shutter curtain moves but a lens opening is stationary right? Not exactly and that’s the problem.
Instead of remaining stationary each time a photo is taken the lens diaphragm opens fully before dialing down to the selected aperture just before the shutter fires. Each time it moves from wide open to the desired f-stop small inconsistencies can occur and show up in our photos.
By selecting a larger lens opening we reduce the amount of movement and thus the chances of experiencing deviations.
Wide aperture shooting isn’t always going to be possible however, especially if we are shooting in daylight and want to drag our shutter. Good thing there are a few easy ways around this and that’s what we are going to be exploring next.
Using Manual Lenses
The easiest way to fully solve the problem is to use a lens with a manual aperture ring. No automatic movement, no flicker.
These lenses were simply designed to use manual external f-stop controls and lack the electronic controls and the forced automatic dialing down. Easily solved but not so easily found, or fit for that matter as most will require some sort of lens adapter.
Now don’t feel like you have to start scouring craigslist for manual lenses if you don’t have any, there’s a quick way to trick your camera into thinking your automatic lens is a manual one. It’s called the lens twist trick and here’s how it works:
The Lens Twist Trick
The lens twist trick basically disconnects your lens electronically while keeping it in place, fooling your camera into thinking it’s a manual lens. If we set the aperture before we disconnect electronic controls then it will remain perfectly constant throughout our sequence of time-lapse shots.
Here’s how to do it:
- Set your desired aperture setting in manual mode
- Press and hold the Depth of Field preview button to set the diaphragm (usually a small black button below your lens)
- Press the lens unlock button and slightly rotate the lens clockwise
The lens is now still connected firmly (well, sort of firmly) to the camera body and it is set and locked at the desired aperture.
This should work for most cameras but if your screen displays an error message and you can’t snap any photos you may need to take extra steps to isolate the lens. Try removing the lens and applying a tiny piece of tape to the electrical contacts on the camera body, then reattach.
Warning: Don’t forget to fully reattach your lens before disconnecting from tripod or packing away.
To learn more:
I've received some amazing feedback on the time-lapse book and am continually amazed by the incredible creative work you guys share. If you are interested in learning more about time-lapse photography you can download a full copy of the book here.
The six most important topics you’ll learn
- Time-lapse gear from basic to advanced: cameras, tripods, intervalometers, ND filters, lenses, and time-lapse motion control devices (motorized sliders, panning, tilting)
- Balancing time-lapse image settings, how to fit all those pictures on your memory card and the important considerations regarding aspect ratio and HD quality
- How to shoot time-lapse: composition, exposure, dragging your shutter and selecting the right time-lapse interval to get the look you want
- Time-lapse flicker: What the heck is it, how to prevent it, and if it does occur how to correct it
- Creating the time-lapse movie: Everything you need to know about time-lapse video software, easy to follow workflows and walkthrough of free and not so free rendering applications, codecs and frame rates, output settings, adding music and effects and where to upload and share
- Test your time-lapse skills! Intro challenges covering astrophotography time-lapse (Astrolapse), flicker free day to night transitions (the time-lapse Holy Grail), HDR timelapses and time-lapse motion control devices
To read the full chapter on flicker prevention including the beginning portion on exposure considerations you can view it here.