Today I got to use the German made Heliopan Variable ND filter and I have to say it’s probably the best out of them all and I have tried them all!
Solid construction, glass apparently from Zeiss. Light control of 1-6.6 stops (0.3 to 2.0 ND density). Markings with hard stops (NOT clicks, it is still smooth, it just has hard end points) so ND is repeatable. It’s also very thin so will vignette on only the widest of lenses. I tried it on my Tokina 11-16 at 11mm on the T3i and only the very corners showed signs of vignetting. It’s tack sharp with no colour shift that I can see!!
It’s surprisingly heavy, actually i would say reassuringly heavy! Though of course there is a downside. It’s not cheap, but few really good things in life are!
You can get it at Amazon.com below or special order from your local retailer. I have the 77mm one, probably the one to go for and you can use step rings for smaller filter lenses.
I managed to get it much cheaper than the below price in Portugal, I paid 225 Euros which is about $330. The Singh-Ray thin 77mm my main Variable ND filter does not vignette at all at 11mm on the Tokina but there is a slight colour shift and it’s not as tack sharp as this or precise but it retails for for just under $400.
On a budget then the newer batch of Light Craft Workshop Fader NDs are still good. I used their superb 4×4 drop in mattebox fader filters on the Alexa shoot and they were superb. Otherwise the new generation of Genus Fader ND filters are also good. It’s just if you want absolutely pin sharpness then this Heliopan is the clear winner.