I am looking to buy a Vari-ND filter. In principal it is two polarizing filters on top of each other. The one i am looking at is the Heliopan 0.3-1.8 filter. But i have a few questions about it.
Does anyone have experience with the Heliopan Vari-ND? Good.. bad, color cast?
Does a Vari-ND always give the effect of a polarizer (blue sky, higher saturation)?
How comes that the lowest setting is one stop? Shouldn´t 2 polarizers eat up more light?
I have never played with a quality custom-purposed vari-ND but several years ago I did buy a B+W KSM LPL to stack on my KSM CPL. I must say that I was not impressed. The range of the filter depends on the focal length you use, with the wider lenses giving you lower max attenuation. When you are near max attenuation you get ugly color casts.
IMO with the advent of great high ISO capability, the only real purpose of a vari-ND is to be able to compose at high attenuation without needing to remove the filter. If I need a 4-stop filter I can always slap on a 5-stop and dial up the ISO a bit to compensate. However, high attenuation is precisely where the VARI-ND struggles. And since they are thick-framed, they vignette on wide lenses. For my needs I find ND filters mounted to a Lee holder much more practical. And now we have a choice of 10-stops and don't have to deal with Lee's chronic ineptness of producing anything close to market demand for their products.
Composing with a strong fixed ND filter on can be tricky, but using live view with the "auto gain" mode enabled helps a lot. In some cases you can still focus and frame with a fixed ND on the camera, so there is less need of using a vari ND, or a filter holder and a slide in filter. This will not work for all situations, but it is another thing to keep in mind if you are trying to avoid the whole vari-ND world.
