OK, I have not got into any masking yet as I generally have not felt the need. But I do have a "problem" negative I need to address. Basically, I have an area of unevenness in the sky down the entire left hand side of the neg, it shows up as an ever so slight difference in sky density. I have not actually taken a density reading yet but I am willing to bet it would need a 5-10% increase or reduction in exposure to make it even, it looks to be about 1/3rd of a stop.

Would there be a way to mask this? The big problem is that it is rather hard edged so it will have to be fairly precise. I'm totally new to this and it seems the perfect candidate for some form of mask...