Doug Kerr
Well-known member
Hi, Bart,
Thanks. Makes sense. I'm embarrassed I never heard of it.
On a matter of terminology, when I said "natural vignetting" I meant what is more often called "fall-off". Natural vignetting (such as the infamous cos^4 falloff) is contrasted with mechanical vignetting, optical vignetting, and sensor angle-of-incidence vignetting.
Thanks again.
Best regards,
Doug
Yes, that's correct. The filter is specifically matched to the lens to compensate for the vignetting / fall-off characteristics of the lens. The filter is darker in the center, and more transparent towards the corners, thus ensuring that the sensor/film gets more uniformly exposed. This prevents underexposed corners, which may otherwise get more noisy in digital systems due to a relatively low photon count.
Of course the amount of vignetting varies with aperture, whereas the fall-off is more constant due to the corner rays striking at a more oblique angle. So it is only a partial (vignetting) solution, but better than nothing.
Thanks. Makes sense. I'm embarrassed I never heard of it.
On a matter of terminology, when I said "natural vignetting" I meant what is more often called "fall-off". Natural vignetting (such as the infamous cos^4 falloff) is contrasted with mechanical vignetting, optical vignetting, and sensor angle-of-incidence vignetting.
Thanks again.
Best regards,
Doug