A frequent question I receive from photographers is "Why are some of my pictures dark and some bright even though I used the same camera settings – the same shutter speed, the same aperture and the same ISO setting – under constant light levels?" Most encountering this problem are very concerned that their camera has a problem – perhaps with the shutter. Fortunately, the camera is not usually the problem. Unfortunately, the resolution of the problem is not as easy as sending the camera in for repair.
The problem images generating the question have usually been captured under fluorescent or gym/arena lighting and a short exposure was often used. Shooting action sports with a fast frame rate is most frequently the source – most of these images will appear properly exposed but an intermittent dark image glaringly appears.
The cause of this problem is usually not the camera, but the light themselves. While those lights may appear to be very constant (and they may indeed be above the flicker fusion threshold/rate where intermittent light appears constant to us), they may not be so. While some lights exhibit very little flicker, some lights are far more intermittent in their output than others. The more intermittent the light output, the more likely that your very short exposure may be timed to coincide with that light's low cycle. And the result is a dark image.
The sun is 100% flicker-free and some light types including tungsten and electronic ballast fluorescent approach this performance. But put a magnetic ballast behind a gas discharge-type lamp and you can prepare for intermittent lighting issues. If your exposure time is long, you might not notice the drop in lighting as much (you may capture an entire illumination cycle or multiple cycles). But when shooting at fast shutter speeds under the flickering lights commonly found in indoor and outdoor sports venues, every shot is a bit of a surprise.
Let me share some light flicker photography examples:
All images in each of the three sets above were taken from consecutive frames in 12 fps bursts from a Canon EOS 1D X with a Canon EF 200mm f/2 L IS USM Lens mounted. The exposure/brightness settings were locked in at f/2 and 1/500. ISO was set at 3200 for the first example and 5000 for the second two. No post-processing changes aside from the Standard Picture Style being selected and sharpness reduced to "1" were applied to these images.
Obviously, the images within each set have vast differences in brightness AND white balance. Even the exit sign goes from bright to dark. This is the point when many photographers begin asking "Is something wrong with my camera?" and "Why is my camera giving me dark images?"
The cause once again is flickering lights. I believe from metal halide magnetic ballast lights in this case.
What do you do about the flickering lights problem?
The best solution to the flickering lights problem involves late-on-the-scene camera technology that I'll discuss at the end of this page. Otherwise ...
One option is to get the venue's lighting upgraded. There are light sources with much less flicker problems available. In fact, the venue the example images were captured in has two indoor fields. The electronic ballast fluorescent lighting used in the constructed-later second field has no flicker issues from my camera's perspective. Replacing a venue's lighting is a bit extreme and not a viable option for most of us.
A great option is to strobe the venue. Securely mount high-powered strobe lights in the venue's ceiling and fire them remotely with PocketWizards. This lighting technique promises the best-possible full-spectrum lighting. The downside is that doing this is somewhat costly, is moderately time-consuming and requires access to the venue's ceiling area (and permission for flash-photography use). If you are shooting many events in the same venue, this strategy might be worth pursuing. For example, if you are shooting all of a university's basketball games for a season, the ideal lighting may be worth the effort and cost required to strobe the arena.
Strobing an outdoor venue is not as frequently done.
The next-step-down bring-your-own-light option is to use an accessory hot-shoe-mounted flash (if permitted). Unfortunately, overpowering the existing lighting at larger venues is tough and the look of direct flash is not ideal. Still, we are talking about improving upon lights that are producing far-from-ideal light in the first place. So, the flash may be the better option.
If opting to use a hot shoe flash, consider using a color correction gel to balance your flash color balance to that most frequently being produced by the existing lights. Max flash sync shutter speeds may not be fast enough if you are not overpowering the ambient lighting. And flash power is reduced if using high speed flash sync.
The option that many (most?) take is to simply deal with the conditions. Shoot in RAW and select an exposure that does not result in blown highlights when the lights are under full output. Shoot a short burst to insure that you have captured a bright frame to check your exposure with. Adjust the brightness of the resulting images as desired during post processing. This of course means adding a significant amount of brightness to the lights-off shots. And since you are likely already using high ISO settings, these images are not going to have great quality. Shoot more images than you need so that you feel more comfortable deleting the poor quality ones.
Adjusting white balance is the other important post-processing step needed for correcting images captured under flickering lights. Your white balance will likely vary greatly from shot-to-shot as it does in my examples above. The best practice here may be to get your primary subject to wear something neutral-colored – perhaps a hair band or wristband. Use that item for your custom white balance adjustment for every shot. Otherwise, hopefully something in your image backgrounds is neutral colored to make proper white balance acquisition easy.
Staged photos often lack something that real game action photos deliver, but when the lighting conditions are terrible, you might want to consider adding some staged shots into your mix. Find out when the venue is not being used (perhaps just before a game) and arrange a time to take your subject(s) and some lighting gear for studio-grade shots.
If you shoot sports (or any similar action) under the lights, you are likely going to experience dark frames in your take-home. Understanding that this could happen will lower your blood pressure and should be your first step in developing a game plan to compensate for the issue. Shooting action under the lights is one of the most challenging types of photography and intermittent lighting is just one of the reasons why.
The Ideal Solution
Let's start with another example. In the top half of the following example are 8 consecutive frames captured in 10 fps burst with a 1/1000 second shutter speed. The subject is a white wall and the lights are fluorescent tubes (I had to go all the way to my basement to find these two sets of four 4' fluorescent tube lights). All images were identically custom white balanced from the center of an optimally-timed image. What you see is the frame capture frequency synching with the light flicker's frequency to cause a different result in almost every frame.
The killer problem for post processing is that the entire frame is not evenly affected. Correcting this issue is a post processing nightmare. The cause of this problem is that, at fast/short shutter speeds, the flicker happens while the shutter curtain is not fully open.
Because the shutter opens and closes only in the up and down directions (with camera horizontally oriented), the area affected runs through the frame in the long direction regardless of the camera's orientation during capture. When the flicker-effected area is fully contained within the frame, the amount of area affected is narrower at faster shutter speeds and wider with longer shutter speeds.
At significantly longer shutter speeds, the effect from the flickering lights is better averaged in the exposures. At 1/25 second, a reference image I captured during the same test looks very nice.
In this light flicker test, I shot at 1/500, 1/1000 (as shown) and 1/2000 seconds. The 1/500 second test showed approximately 2/3 of the frame severely affected at most, but the 10 frames captured around the most-effected frame had various amounts of one frame edge strongly affected. As you would expect, the 1/2000 second test showed an even narrower band of the flicker's effect running through the image (a smaller slit of fast-moving shutter opening being used), but ... I'm guessing that there are not many venues with flickering-type lighting strong enough to allow use of this shutter speed at a reasonable ISO setting. The 1/500 and 1/1000 settings are more real world settings.
The bottom set of results show off the best solution to the flickering light problem: Canon's awesome Anti-flicker mode, as first seen on the Canon EOS 7D Mark II and now found on many camera models since. The only difference in the capture of the second set of images was that Anti-flicker mode was enabled. These were a random selection of 8 consecutive frames, but the results from all Anti-flicker mode enabled frames were identical regardless of shutter speed tested. I'm not going to say that these results are perfectly-evenly lit, but ... they are dramatically better than the normal captures and you will not see the less-than-perfectly-even lighting in most real world photos without a solid, light-colored background running through the frame.
When enabled (the default is disabled), Flicker Mode adjusts the shutter release timing very slightly so that the dim cycle of the lighting is avoided. In single shot mode, the shutter release lag time is matched to the light flicker cycle's maximum output. In continuous shooting mode, the shutter lag and the frame rate are both altered for peak light output capture. In my tests above, the frame rate was reduced by 1-2 fps and shutter lag can be affected, making the camera feel slightly less responsive.
When flicker is detected but flicker mode is not enabled, a flashing Flicker! warning shows in the viewfinder. The FLICKER warning shows solid when a flicker is detected and the camera’s setting is enabled. Flicker detection has worked very well for me. From my own basement to an indoor sports venue to a trade show floor, I've seen the flashing "Flicker!" warning and enabling the Anti-Flicker mode has resulted in optimal image capture.
Since the viewfinder's metering system is required for flicker detection, this feature is not available in Live View mode (due to the mirror being locked up). The mirror lockup feature is also disabled when Anti-flicker mode is enabled. The owner's manual indicates that Flicker mode is not going to work perfectly in all environments.
In the test I shared above, flicker avoidance was perfect 100% of the time. I shot a soccer match at an indoor sporting venue with a complicated economy lighting system. In that shoot, the Anti-flicker mode was successful about 98% of the time in the about-350 images I captured. The post processing work required for this shoot was exponentially lighter than any of my many prior shoots at this venue. Sean's experience shooting an NCAA Division 1 football game under the lights was very good, but perhaps not as good as my 98% experience.
Canon's Anti-flicker mode is a game changer – it will save the day for some events. This feature alone is going to be worth the price of the camera for some photographers. A camera with this technology is easily the best answer to the flickering lights problem.