Slow and long exposure photography could give us pleasant results if done properly. And this is a part of photography that I love to learn more, and practice more because there are so many things to learn. Even the easiest thing, the technical side sometimes still being overlooked and not done properly. So there is no other thing to say then keep on learning and sharing. As for the technique I will make another post, but here I will share one simple mistake that could ruin the day for you.
This time it is about light leaks, yes it is really stray light leaking from sources that made it to the camera sensor during the photo taking process. Long exposures take a long time and the small leaks must be accounted for, as it will create problem. The most common problem is forgetting to close the eye view finder during. On my full frame camera the eye view finder have a slider for closing the view and preventing light from leaking, so it is easy to do. But on my APSC/DX camera the eye view finder are not equipped with the slider, and it have a separate view finder blocker to be attached, so most of the time it is easier to have a piece of cloth closing the view finder.
Another important factor that added the light leak is the direction of sun towards the view finder. With the sun coming from the side and/or behind of camera, there will be more light leaking as photo above. The result is so obvious, the light leaked so bad that its pink color totally ruined the photo. But just remember this, because sometimes out on the field things could be so confusing when we are not aware that it is light leak not color cast from the filter being used.
When the direction of sun is coming from the front of the camera, the light leak could be very weak that could go unnoticed. For example, see the photo below from this post. The leak is not so visible, but we can see it at the rocks in the middle of the photo. It looks like an ordinary colored rock, but it is a leak.
So for this post conclusion is that never forget close the rear eye view finder while you are doing slow or long exposure, either by sliding the eye view finder lever or using cloth to protect light from entering the view finder. Or use both if possible.