Hi,
I shot the attached picture to test Heliopan 95mm Neutral Density Slim (ND) 3.0 Filter on the Hasselblad HCD 28mm f/4.0 Wide Angle Prime Lens.
ISO 100, 6 sec, f/8.0.
The picture is exported from PHocus as unprocessed JPEG Medium Size.
I think this amount of vignetting is not accessible.
How much vignetting should be expected from 3.0 to 4.5 ND filters on wide angle Hasselblad HCD 28mm lens.
How to eliminate or reduce vignetting at shoot time?
Can Phocus help to eliminate vignetting in post production? Please give a step by step detailed instruction, if possible.
Hi Evgeny,
The oblique rays have a longer path to travel through the thickness of a mass colored filter than the chief rays. That's why they will always pick up more density or color from such a filter. In addition, some (non-retrofocus) wide angle lens designs will cause some shading effects on digital sensors as well, in addition to the lens vignetting and light fall-off.
I'm not familiar enough with Phocus, but what you need is a solution that's called LCC in the Capture One Pro Raw converter. Maybe Phocus has a similar solution, I just don't know.
You can also try RawTherapee, a free Rawconverter, which handles all sorts of file formats, and it can automatically remove the type of vignetting you are experiencing if you supply it with one or more flat-frame shots taken with the the lens and filter set at the same focus distance.
Cheers,
Bart