Uh… - I missed that one. So you already captured an empty film gate. Let’s have a look at that data, slightly contrast-enhanced:
The darker spots, some approaching in shape a pentagon, are dirt, either on your lens or your sensor. That’s nothing I would be bothered about.
There are some broad bands visible - they are horizontal. Like the noisestripes we are discussing. But they have a totally different spatial extend (coherence). They are much broader than the noisestripes. These are most probably caused by the powersource of your illumination.
Most noteably, there are no noisestripes visible which extend only over a few horizontal lines. Those lines seem to occur only in dark image areas.
Two other, magenta-like broad stripes are also visible. One vertical one, on the left side of the gate, another one horizontal at the bottom. Both are most probably caused by reflexion and shadowing in the path from LED to gate.
All in all, your gate is resonably flat as it should be. But as @PM490 mentioned:
…
Yes, there is. Think about the sprocket hole.
The “As Shot Neutral”-tag in the .dng reveals it. It is
As Shot Neutral : 0.3460207612 1 0.476213153
which translates into red gain = 2.89 and blue gain = 2.01.
Any dirt which is not on your sensor. That is, dirt on the lenses (even internal ones). I would not bother about this. It’s is unnoticable in any scan you are going to do.
So we didn’t hit the black cat in this try… Frankly, I do not know what is happening here. What really is hard to understand is why some frames show more noise than others, under otherwise identical capture conditions. Maybe it’s EMI (electromagnetic interference) from an external appliance. I guess that’s a project for another day. Currently, I have no clue what is causing these stripes and especially the variations we are observing over time and different installations.
PS: did you notice this thread? Your lens might not have it, but it might be also a source of interference.