Graduated ND filters for bright skies

If you've ever shot a video with a bright sky in the top of your shot and dark foliage below, you've undoubtedly experienced the problems of exposing an image for such a situation - and it usually winds up with your clouds blown out to bright white in order not to underexpose the rest.

Since it is difficult - and often impossible - to post-process multiple exposures with video (as is sometimes done in photography), bracketing techniques are not an option.

For this reason, you might have already dug up these little critters - graduated grey ND filters which screw onto the front of your lens and gradually shut out light where you don't want it:

Unmarked 52mm on the left, KOF Concept 72mm on the right.

Unfortunately, they don't work. Not well, anyway.

Why?

1.
The location of your gradient is fixed. You can rotate the filter 360 degrees on the front of your lens, but that won't help you much when your horizon line isn't in the upper-third of your frame.



2.
The amount of reduction is minimal. Normally, a non-graduated ND filter is marked by the number of f/stops it reduces exposure, e.g.: ND2, ND4, ND8, etc. The two examples above are not marked with anything (nor are they sold as having any particular reduction), so the amount of ND reduction you're getting is unknown. Tiffen's graduated ND filters are sold as ND0.6, so we'll assume the 52mm Chinese knockoff is a copy of the same.

As there is nothing better to illustrate this than an example, following are a pair of comparison shots, taken at the same exposure:

Without 52mm graduated grey ND0.6 filter

With 52mm graduated grey ND0.6 filter

The filter does help, but I could have used at least another stop of reduction (if not close to two, if the palm trees at the left were not present). My experimentation with the 72mm KOF Concept filter did show much of a performance difference to the generic 52mm.

 
3. 
You can't use these with step-up adapters, because of problem #1 - the fixed gradient. If you were to put the 72mm filter on a 52mm lens (shown at right), the 52mm lens will only see a small portion of the gradient - not enough to make a difference.




This is where the alternative steps in - Cokin P-style, slide-in, graduated ND filters:

Given that the design allows one to put the gradient wherever they please (and vary the amount of reduction depending on the ND glass used - my set came with ND2, 4 and 8), it is considerably more versatile than the screw-on type (and it isn't affected by step-up rings).

Following are the results of a few minutes of experimentation with the graduated ND8, all shots taken at ISO 125, 1/320 shutter, with my Nikon 50mm (with a 52mm thread stepped up to meet the adapter's 72mm threads) at f/4:

No filter

Filter approximately centered in the holder

Filter level with top of filter holder

I'd say the centered ND8 is about as even an exposure one could ask for before going to color grading. Definitely better than the results from the thread-on filter.

-Kurt "Man with the 5D"

No monetary compensation was provided for the mention of the any of the products mentioned or shown in this article.