Timelapse color flickering

Question

I've tried to shoot the red line of sunrise along the sea and I've done that from under a very low bridge with the penumbra, so I' ve captured some portions of the sand and palm trees too. I tried it twice but even if I shot with a manual lens and camera settings I gained a color flickering between some pictures, and it occurs until ten minutes before the golden hour.

My manual lens is a "Nikon 28mm 2.8 ai-s" which turns into a 42mm on my Nikon d3200 camera. Of course I used an intervalometer and shot in RAW.
The first time my settings were:

• shutter speed - 1/20, diaphragm closed to 8, exposure meter set to 0, iso 200, 13 minutes shoot time, 3 seconds of interval.

The second time they were:

• shutter speed - 1/15, diaphragm closed to 11, esposure meter set to +2, iso 400, 25 minutes shoot time, 4 seconds of interval.

Both times I set white balance to - direct sunlight. Sometimes the colors change tonality, the sand becomes purple and the sky changes colour from blue/dark blue to light blue. There has been an exception though when I set my values in another different way:

• shutter speed - 1/20, diaphragm closed to 5.6, exposure meter set to +5, iso 400, 12 minutes shoot time, 4 seconds of interval. In this last case there weren't clouds in the sky and everything was brighter, no color flickering occured.

I read that when there's no much light the camera could not interpret colours in the same way, but I find it bizzarre. Why does the camera read colors differently at every shot and why it doesn't do that in normal video mode?
How can I solve this problem? I planned to make new shots outside the bridge, maybe something can change. I am hopeful it is just an incorrect setting. Is ND filter necessary?
I'm just interested now in timelapses then I'm a beginner.

Answer 1

What you are experiencing is the shot-to-shot variability that is a natural consequence of the mechanical linkage between the Nikon camera body and lens. It's why other camera companies (Minolta and Canon) went to an all electronic mount as early as the late 1980s. This same question has been asked and answered before: How can I cancel aperture resetting between subsequent image shots of a timelapse?

Thanks for answering, but I don't understand what is the connection between my analogical lens (ai-s) and the explanation inside your link. I can only use my Nikkor 28mm in manual mode otherwise the camera body doesn't detect it. This doesn't mean I can display the exposimeter and the diaphragm's aperture but I can see the shutter speed. My Nikon d3200 affects the lens in no way because it is independent from the body, in fact it has a metal ring for switching the aperture and once I've done it stayes fixed all the time.
Even if I disconnect the lens nothing happens because I set up my camera in manual mode, I can still continue to take pictures. Simply it's an analogical tool that I mount on the body which doesn't interfere. To know how much the diaphragm's aperture affects the image, I just go in live view and I adjust it accordingly.

So, why do I obtain color variations between some frames sometimes?