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First time in a while I've done a long exposure, either the lens Nikkor 24-70 or the camera body D800 is suffering from light leakage, it seems to happen only at certain focal lengths. This is one of the few images this morning to escape the light leak mark!
It's going to be an evening of internet trawling by the looks of it, I hope its an easy fix because I cannot afford to replace either!
If you have happened to have suffered this then any info is valuable!