Photography Problems: Pink / Purple Lines on Long Exposure Images with ND Filters
I noticed pink / purple lines on the resulting images of my long exposure shots with my DSLR camera on sunny days and ND filters applied.
There are different neutral density (ND) filters on the market which enable completely new possibilities of photography. I really like "big stoppers" like this one*. They can be fixed right in front of a lens and add a lot of aperture steps. This allows long exposure shots on sunny days to create, for example, a soft water surface or blurred clouds.
The Problem
During my first tries, I noticed some purple / pink / orange and sometimes green horizontal lines on the images. They appeared every time and the problem could be reproduced. Here is an example:
I first thought a little light would pass between the lens and the filter onto the sensor. But I was pretty sure everything is 100% tight. At home, I tried and googled a lot and found the root cause of the problem: the camera viewfinder!
When I was taking the photo above, sunlight came in from the viewfinder onto the sensor. I made some experiments to validate it by aggressively bringing light into the camera with a simple flashlight pointing to the viewfinder.
And yeeep, this results in a broken image again:
The Solution
Okay, great, problem identified! But how to solve this? There are some small plastic clips on the market that are called eyepiece caps* (just search for the correct one for your camera model) . Add them onto the camera viewport and everything should be fine.
The same shot, on the same day, with the same settings and a flashlight pointing to the viewfinder with the eyepiece cap on it solved it.
