Variable ND filter size

[AndreasOberg]

Im wondering what size I should get of variable ND filters. Canon doesnt have any lenses bigger than 77mm but I see that many uses 82mm. Is there a reason I have missed? Any insight would be appreciated.
/Andreas

 

[ericyoung]

Adding the thickness of the two rings of a variable ND filter can cause vignetting on wide lenses. Using a step up ring from 77mm to 82mm prevents any possible vignetting.

If you never shoot wide lenses, this isn't necessary.

Note that on ultrawide lenses, the polarising effect can result in uneven skies, or large flat coloured areas.

 

[Jason Comparetto]

I believe that there are several lenses that Canon makes that are larger than 77mm... I'm thinking of the 16-36mm Version II off the top of my head. And as Eric has stated, wide lenses will require a stepup ring to prevent vignettting.

 

[AndreasOberg]

Aha, avoiding vignetting sounds very useful. Do you think it would be useful to have several different ND filters or would you just use one with stepup rigns?
Best wishes
/Andreas

 

[ericyoung]

Just one with step up rings is the cheapest way.

But as I said, VariNDs can introduce a colour tint, and because they are polarising filters, they have all the artifacts that polarisers have.
Most also let InfraRed through, so you should have a InfraRed cut filter available for when IR pollution presents itself.

 

[AndreasOberg]

Would you recommend using them at all for documentaries for example or should I use something else? They seem convinient but Im a bit concerned about issues

 

[ericyoung]

They are great for fast changing, unpredicatable stuff like documentaries - trying to change NDs on your own in challenging environments will get in the way of your shooting. Mark Toia uses them a lot for run and gun style shooting, but then will go for full mattebox and individual filters when he has a camera crew and a more controlled environment.

Like anything you have to decide on your priorities if your budget is limited, and pick the best option for your particular styles of shooting, and maybe rent the alternatives for your less usual shoots.