If you have experimented with long exposure photography, you may have seen light leakage issues in your images. For the uninitiated – your camera is a light tight body that is intended to allow light from one end only, and that’s the front of the lens. Light only enters when you press the shutter release. Normally, your camera wouldn’t allow light to enter through any other opening in the camera. However, unless you have a badly manufactured camera, there is typically only one source that could potentially harm your images, and that’s your camera’s viewfinder. Let’s talk about what you can do to mitigate light leaks during those long exposures.
The Source of the Problem
As I have pointed out, the chief culprit is the viewfinder. Being essentially a small optical path that receives light bounced off the prism and mirror inside the camera, it often does the reverse of its job too. Light enters through the viewfinder and bounces off the prism and mirror and then goes onto the sensor. Normally, you wouldn’t see this as a problem, but when you are taking long exposures, it can create major issues. This is not unique to digital cameras only, film camera have this issue too. However, compact cameras and those without an optical viewfinder do not suffer from this particular problem.
Some photographers find it hard to identify the source of the problem. Many complain that it is their ND filter that caused weird light streaks in images. If you have been thinking the same, perhaps it is time to revisit this topic again – you might find your ND filter to be perfectly fine! The problem in that case most likely lies somewhere else, specifically in the viewfinder.
Light Leaks in Images
Weird bands of color will appear in the image. They are also referred to as ‘light streaks’ because that’s what they look like – weird random bands of light. They could be horizontal as well as vertical. They are particularly exasperating for a landscape photographer, who may have had set his camera to shoot a slow shutter speed time-lapse and after several hours of shooting gets thousands of photos with light streaks on them. A truly annoying and frustrating experience!
Why Light Leaks Affect Long Exposures More Than Normal Exposures
When you make long exposures, there is that much more time for even a small amount of light leak to create strong streaks in the image. Normal exposures lasting for only a fraction of a second wouldn’t be enough for light leakage to really affect an image.
Since photographers normally shoot long exposure images using ND filters, these filters, or sometimes even lenses are usually blamed for this problem (yes, some lenses can potentially create light leaks as well, but that’s rare and typically happens on very long exposures).
How to Eliminate Light Leaks
There is a lengthy and complicated process to fix light leakage using Photoshop or other photo editing tools, but the results may not be very convincing and it is often too much work to even bother trying to fix such leaks in post. If you have a lot of images to edit, it is far easier to shoot them all over again, than going through that nonsensical post-processing workflow. It is easier to prevent them from happening in the first place, rather than try to overcome them afterwards.
The prevention is rather simple. Either compose your shot through the viewfinder, then cover it before starting the exposure, or cover the viewfinder up first and use Live View on the LCD of your camera to compose your shots (I prefer the latter method to avoid going back and forth). To cover the viewfinder you can use a piece of black Gaffer tape. It stops light from spilling into the camera. Remember how photographers back in the day used to cover the camera and themselves with black cloth to prevent light from leaking into the camera? The idea is the same. For those of you who have cameras with a built-in viewfinder shutter or a cap, it is a much easier process. If you are a Nikon user, most of the pro bodies would have that viewfinder shutter. For cheaper entry level DSLRs, however, the only good solution is to use Gaffer tape to seal off the viewfinder.