Every now and again I get a distinct green line or colour cast in the lower third of my photos. This can (but seldom) happen when I’m shooting wide (say 16-20mm), using my Lee 3 stop grad soft GND (100mm x 150mm) with the shot angled away (say 40-70°) from the rising sun.
Other factors in play are I think dark-ish, dawn shots. A small tilt down of the camera so the horizon is higher in the frame. The GND is pushed up in the holder to align the transition line to the horizon. This said, it appears to me that the green hue or line comes from the clear section of the GND.
Here’s an example from yesterday at dawn, 30 minutes before sunrise (on the RHS).
5Ds + 16-35mm f4 L at 16mm.
10, 25s, ISO 400.
The green line can be seen in line with the bottom of the kayak. This would be maybe 25% up from the bottom of the filter, well into the clear section of it.
From the same shoot I have say 60 images, 3 of which have this line. All are wide, taken at dawn and a similar aspect to the attached. The other say 57 are wide too, use the same filter, have a tilt, angled away L & R from the rising sun or straight into the rising sun. But no green line.
Could the age of the filter be in question? Purchased 2011.
Mark, I can’t say I’ve ever had this show up on any images using ND filters, but the caveat is I shoot only film. Do you recall if this is the extreme bottom edge of the filter. Maybe its a bit of CA - chromatic aberration. It usually shows up on film as magenta, cyan, or greenish. If you use any anti-CA software plugins you might try it to see what happens to the green line. It is very faint and with some work can be cleaned up manually I would think.
Perhaps its not the filter at all but a combo of the camera and lens at low light, long exposure and the angle of light entering the lens.
The NPN article on CA suggests closing the aperture (I shoot f11 99% of the time) to increase the DoF. But of course doing this means a longer exposure time so maybe not.
That is a bit more complexing. I thought it was the very edge of the filter bottom. I assume you’re not using any chemicals to clean the filter like Windex. But even that straight of a line would have been on the extreme edge of the filter and not 25% up and that perfectly straight.
Shooting digital at least your not getting any scanning artifacts we film shooters see at times.
Let us know if you find out the culprit. Good luck.
At first I thought the green area followed the curvature of the lens, but on enlargement, it seems to curve up from left to right but then down on the right side toward the water. I also see a vertical line up the far right side upon enlarging the image. If you have access to another GND it might be helpful to take a some shots with it followed by some with the potentially flawed one. Other than that I have no idea what is causing it. Might be time for a new filter.
